A review of copper fertilizer management for optimum yield and quality of crops in the Canadian Prairie Provinces

Transcription

1 A review of copper fertilizer management for optimum yield and quality of crops in the Canadian Prairie Provinces S. S. Malhi 1 and R. E. Karamanos 2 1 Agriculture and Agri-Food Canada, P.O. Box 1240, Melfort, Saskatchewan, Canada S0E 1A0 ( malhis@agr.gc.ca); and 2 Western Co-operative Fertilizers Limited, Calgary, Alberta, Canada. Received 25 July 2005, accepted 13 February Malhi, S. S. and Karamanos, R. E A review of copper fertilizer management for optimum yield and quality of crops in the Canadian Prairie Provinces. Can. J. Plant Sci. 86: Deficiency of copper (Cu) in Canadian prairie soils is not widespread, but whenever it occurs it can cause a drastic reduction in seed yield and quality of most cereals, especially wheat. Field experiments conducted in western Canada indicated that broadcast-incorporation of granular Cu fertilizers prior to seeding at kg Cu ha 1 was usually sufficient to prevent Cu deficiency in wheat, and improve seed yield and quality. At lower rates (< 2.0 kg Cu ha 1 ), broadcast-incorporation of granular Cu fertilizers was not effective, while surface spray-broadcast followed by incorporation of liquid Cu fertilizers was much more effective in increasing seed yield of wheat in the first year of application. Surface-broadcast without incorporation and seedrow-placed granular Cu fertilizers were much less effective in improving seed yield of wheat than their foliar or soil-incorporated applications. In the growing season, foliar applications of Cu at 0.20 to 0.28 kg Cu ha 1 to wheat at the Feekes 6 (first node of stem visible at base of shoot or stem elongation), Feekes 10 (sheath of last leaf completely grown or flag-leaf) and early boot growth stages were very effective in restoring seed yield, while Cu applications at the Feekes 2 (four-leaf) or Feekes 10.5 (complete heading) growth stage did not have a consistent effect to correct damage caused by Cu deficiency. Some Cu fertilizers (e.g., Cu oxide) were less effective than others in preventing/correcting Cu deficiency. Soil application at relatively high rates produced residual benefits in increasing seed yield for a number of years. The sensitivity of crops to Cu deficiency is usually in the order (wheat, flax, canary seed) > (barley, alfalfa) > (timothy seed, oats, corn) > (peas, clovers) > (canola, rye, forage grasses). Stem melanosis in wheat was associated with deficiency of Cu in soil, and the disease was reduced substantially with Cu application. A high level of available P in soil was observed to induce/increase severity of Cu deficiency in wheat. Soil analysis for diethylene triamine pentacetic acid- (DTPA) extractable Cu in soil can be used as a good diagnostic tool to predict Cu deficiency, but there was a poor relationship between total Cu concentration in shoots and the degree of Cu deficiency in crops. Application of Cu fertilizers to wheat on Cu-deficient soils also generally improved seed quality. Key words: Application time, Cu source, foliar application, granular Cu, growth stage, placement method, rate of Cu, seedrow-placed Cu, soil incorporation, wheat Malhi, S. S. et Karamanos, R. E Optimisation du rendement et de la qualité des cultures dans les provinces des Prairies canadiennes grâce à l utilisation d engrais cupriques. Can. J. Plant Sci. 86: La carence en cuivre (Cu) n est pas très fréquente dans les Prairies canadiennes, mais là où elle existe, on note une baisse draconienne du rendement grainier et de la qualité de la plupart des céréales, particulièrement le blé. Des expériences sur le terrain effectuées dans l ouest du Canada révèlent que l épandage à la volée puis l incorporation au sol d un engrais de Cu granulaire avant les semis, à raison de 3 à 5,6 kg de Cu par hectare, suffit à prévenir une telle carence chez le blé, tout en améliorant le rendement grainier et la qualité de la culture. À un taux plus bas (< 2,0 kg de Cu par hectare), l épandage à la volée et l incorporation au sol de l engrais de Cu granulaire manquent d efficacité, tandis que la pulvérisation en surface et l incorporation au sol d un engrais liquide accroissent nettement davantage le rendement grainier du blé l année de l application. L épandage à la volée d un engrais de Cu granulaire sans incorporation au sol et le placement avec les semis sont manifestement moins efficaces qu une application foliaire ou que l incorporation au sol au niveau du rendement grainier du blé. Durant la période végétative, l application foliaire de 0,20 à 0,28 kg de Cu par hectare au blé aux stades Feekes 6 (premier nœud de la tige visible à la base de la plantule ou élongation de la tige), Feekes 10 (gaine de la dernière feuille complète ou feuille paniculaire) et début du gonflement rétablit très efficacement le rendement grainier, alors qu une application de Cu au stade Feekes 2 (quatre feuilles) ou Feekes 10.5 (épiaison) ne corrige pas toujours les dommages résultant de la carence. Certains engrais cupriques (par ex., oxyde de cuivre) préviennent ou rectifient moins bien la carence en cuivre que d autres. Appliqués au sol à un taux relativement élevé, ces engrais ont des effets résiduels en augmentant le rendement grainier de la culture plusieurs années par la suite. La sensibilité des cultures à la carence en cuivre suit habituellement l ordre que voici : (blé, lin, alpiste roseau) > (orge, luzerne) > (fléole, avoine, maïs) > (pois, trèfle) > (canola, seigle, graminées fourragères). On associe la mélanose de la tige du blé à la carence en cuivre dans le sol et l application d un engrais cuprique atténue de manière appréciable les dommages attribuables à cette maladie. Une forte concentration de P disponible dans le sol induit ou intensifie la carence en Cu chez le blé. Le dosage du Cu extractible au DTPA dans le sol est un bon outil de diagnostic pour prévenir la carence en cuivre, mais la concentration totale de Cu dans les pousses est mal corrélée au degré de carence en Cu dans la culture. L application d engrais cupriques au blé sur les sols carencés entraîne généralement une amélioration de la qualité des semences. Mots clés: Mmoment d application, source de Cu, application foliaire, Cu granulaire, stade de croissance, méthode de placement, taux de fertilisation Cu, placement de Cu avec les semis, incorporation au sol, blé 605 Abbreviations: DTPA, diethylene triamine pentacetic acid; WP, whole plant shoots; YFEL, youngest fully emerged leaf

2 606 CANADIAN JOURNAL OF PLANT SCIENCE Copper (Cu) is essential for plant functions such as chlorophyll production, protein synthesis and respiration (Bussler 1981). Cereals took up 2.2 to 8.1 g Cu ha 1 in grain and 6 to 26 g Cu ha 1 in straw in a study in Saskatchewan covering 51 site-years (Kruger 1984). In the Prairie Provinces (Alberta, Saskatchewan and Manitoba), deficiency of Cu is not widespread, but whenever it occurs it can cause a serious reduction in seed yield (up to 50%) and quality of wheat (Karamanos et al. 1986, 2004; Malhi et al. 1989; Piening et al. 1989). Copper deficiency in wheat and other cereals produces characteristic symptoms of yellowing and curling of young leaves, pigtailing of leaf tips, limpness or wilting delay in heading, aborted heads and spikelets, head and stem bending (Graham and Nambiar 1981; Robson and Reuter 1981), as well as stem melanosis disease in certain wheat cultivars (Piening and McPherson 1985). Organic (peat) soils often respond dramatically to Cu fertilization (McAndrew et al. 1984; Karamanos et al. 1985b). Dowbenko et al. (1989) estimated that approximately ha of organic soils are under cultivation in Manitoba, and studies by Reid (1982) and Tokarchuk (1982) established that Cu deficiency is a major limitation to small grain production on these soils. Copper deficiencies have also been established on organic (peat) soils in Alberta (Hartman 1992) and Saskatchewan (Karamanos et al. 1985a, 1991). Copper deficiency has also been observed on coarse textured mineral soils (Caldwell 1971; Kruger 1984; Kruger et al. 1985; Lowe and Milne 1979); it usually occurs in irregular patches within fields. The extent of Cu deficiency is not well defined but 1.2 M ha in Alberta (Penney et al. 1988) and just over ha in Saskatchewan (Kruger et al. 1985) have been identified as potentially deficient in Cu. In the Canadian prairies, agronomic issues of Cu nutrition in crops have come to the forefront due to the recognition of Cu deficiency on some soils and the availability of many Cu fertilizer products for soil or foliar application (Table 1). Yield response of cereals to Cu fertilization has been investigated in western Canada (Karamanos et al. 1985a, b, 1986, 2003, 2004, 2005; Karamanos and Goh 2004; Malhi et al. 1989; Piening et al. 1987, 1989). Soil incorporation of granular Cu fertilizers at rates of 3 to 5.6 kg Cu ha 1 has been recommended to prevent Cu deficiency in crops on Cu-deficient soils (Saskatchewan Agriculture and Food 2000). Because Cu fertilizers are costly and many growers have adopted minimum tillage practices, most producers usually apply much lower rates of Cu (often less than 1 kg Cu ha 1 ) as foliar, band or seedrow-placed with little soil disturbance. For economic reasons, producers are interested in information regarding relative effectiveness of different Cu sources, rates, formulations, times and methods of placement to prevent, as well as correct, Cu deficiency in wheat and other crops. The objective of this review is to summarize Cu deficiency research information from various experiments conducted in the Prairie Provinces of Canada on various crops. These experiments have dealt with Cu fertilizer rate, source, formulation, time of application, placement method, balanced fertilization, and soil/plant test issues in relation to seed yield and quality of several crop species/cultivars. The indicators considered in this review are seed yield, seed quality (protein, hectolitre weight, 1000-kernel weight, Cu concentration), Cu uptake, recovery of applied Cu and residual diethylene triamine pentacetic acid (DTPA)- extractable Cu (Lindsay and Norvell 1978) in soil. For practical utility of the research information, preference has been given to results obtained from field experiments relative to experiments carried under controlled conditions. IDENTIFICATION OF COPPER DEFICIENCY In order to arrive at an appropriate rate of Cu application for economic and environmental benefits, a reliable prediction of plant-available Cu in soil during the crop growing period is needed. Earlier research in western Canada showed that DTPA-extractable Cu (Lindsay and Norvell 1978) is a good measure of available Cu in soil, and that seed yield response of wheat to Cu fertilizer could be expected in soils containing < 0.4 kg Cu in the top 15 cm depth (Kruger et al. 1985; Karamanos et al. 2003). Karamanos et al. (2004) showed that concentration of DTPA-extractable Cu in soil does not change during the growing season and from year to year. This suggests that soil samples can be used as a reliable tool for assessing the status of available Cu in farm fields at any time. Penney et al. (1988) reported Cu deficiency symptoms and seed yield response of wheat to Cu fertilizer on soils containing as much as 0.8 mg DTPA-extractable Cu kg 1. The critical level of 0.2 mg DTPA-extractable Cu kg 1 suggested by Lindsay and Norvell (1978) has been adopted by the province of Manitoba (Manitoba Agriculture, Food and Rural Initiatives 2004), but not Alberta and Saskatchewan that adopted different critical levels (0.6 and 0.4 mg kg 1, respectively) (Alberta Agriculture, Food and Rural Development 1995; Saskatchewan Agriculture and Food 2000). However, soil tests for Cu do not always provide accurate indication of available Cu in soil, especially on soils marginally deficient in Cu (Mortvedt 1977). Limitations arise due to the inherently high spatial variability of available Cu in soil. Singh et al. (1985) were able to explain only a small portion of this variability in soil on the basis of organic matter, translocation through the solum and depth of genetic horizons. A small portion of soil sample from areas with high Cu can thus skew the assessment of soil Cu status in a composite sample produced from many cores collected throughout the field (Karamanos et al. 2003). A fractionation experiment on 27 Saskatchewan soils indicated an average total Cu content of 21.0 mg kg 1 (range of mg kg 1 ), and Cu availability was associated with oxides, organic matter and total Cu, but clay content is the key soil property affecting Cu availability (Liang et al. 1991). Residual Cu, which is essentially Cu held within the silicate mineral structures, comprised % of total Cu. In addition to soil texture, organic matter, ph, other nutrients and subsoil Cu levels can also be an important factor in affecting Cu availability and subsequent yield response to applied Cu fertilizer (Solberg et al. 1996; Table 2). They reported that Black Chernozemic soils containing low but similar Cu levels in both surface and subsoil showed severe Cu deficiency in wheat. On the other hand, Gray Luvisolic soils with low Cu levels in the surface soil, but

3 MALHI AND KARAMANOS MANAGEMENT OF CU FERTILIZERS 607 Table 1. Characteristics of Cu fertilizer products used in field experiments Cu content Cu fertilizer product Trade name z Chemical formulation or concentration Product producer or distributor Cu lignosulphonate (granular) Micro Tech Cu lignin sulphonate 5% RSA Micro Tech, Seattle, WA, USA Cu sulphate (granular) Copper sulphate Cu SO 4 5H % Pestell Minerals and Ingredients, New Hamburg, ON, Canada Cu oxysulphate I (granular) Cu 15% Micro Mix Cu treated with H 2 SO 4 15% Cameron Chemicals, Inc., Portsmouth, VA, USA Cu oxysulphate II Frits-220G Cu treated with H 2 SO 4 20% Frit Industries, Ozark, AL, USA Cu chelate-edta liquid Tiger EDTA Cu EDTA g L 1 Tiger Industries, Calgary, AB, Canada Cu sequestered I (liquid) Tiger foliar Cu complexed with lignin sulphonate 61.1 g L 1 Tiger Industries, Calgary, AB,Canada Cu sulphate/chelate (granular dissolvable) Pro-Sol Cu CAC Copper sulphate citric Acid EDTA 20% Frit Industries, Ozark, AL, USA Cu sequestered II (liquid) PhosynCoptrel 500 Cu oxychloride 500 g L 1 Phosyn Canada, Grand Falls, NB, Canada z The use of trade names, proprietary produce or vendor does not imply endorsement by authors or Agriculture and Agri-Food Canada. Table 2. Change in DTPA-extractable Cu (mg Cu kg 1 ) with depth in two Black Chernozem and two Gray Luvisol soils in Alberta (prepared from Solberg et al. 1996) Black Chenozem Gray Luvisol Sample depth (cm) high Cu levels in the subsoil did not show any evidence of Cu deficiency in wheat. In-crop assessment of nutrient deficiency/sufficiency also has potential to improve nutrient management and reduce environmental risk. Visual symptoms (Graham and Nambiar 1981) usually occur when the crop is moderately to severely lacking in Cu. The greatest limitation of visual Cudeficiency symptoms is that seed yield losses in cereals can occur before visual symptoms are evident. Moreover, visual symptoms can be confused with those caused by herbicide injury or frost (Solberg et al. 1996). Nevertheless, visual diagnostic can be an effective tool when combined with soil and tissue testing. Plant tissue testing can also be used to determine plant Cu deficiency. But, in general, information provided by this method may be too late to correct the Cu deficiency problem and restore seed yield to the optimum level for the current crop. Concentration of Cu in plant tissue varies with crop species and cultivars, and usually declines as plants develop (Gladstones et al. 1975; Solberg et al. 1996; Table 3). For example, in Alberta where plant samples were collected from 12 barley fields with severely deficient to adequate Cu levels, Cu concentration in shoots declined from 6 to 3 mg Cu kg 1 as dry matter increased from 1290 to 6460 kg ha 1 in the growing season (Solberg et al. 1996). Karamanos et al. (2004) have also shown a decrease in Cu concentration in plant tissue of wheat with plant age. In their study, Cu concentration in plant tissue was about 7 mg Cu kg 1 at Feekes 6 and decreased to about 4 mg Cu kg 1 at Feekes 10 growth stage. The lower Cu concentrations at advanced growth stages were associated with a dilution effect of increased dry matter. In the Canadian Prairies, researchers have made attempts to separate responsive and non-responsive sites based on Cu concentrations in plant tissue at various growth stages (Karamanos et al. 1986, 2004; Solberg et al. 1996). Using a combination of visual inspection (Black 2000) and tissue analysis, Karamanos et al. (2004) determined that seed yield responses of wheat to Cu fertilization can be obtained when Cu concentrations in wheat tissue at Feekes 6 and Feekes 10 were less than 3 and 2.5 mg Cu kg 1, respectively. They indicated that the visual method provided an additional diagnostic tool to decide whether a second foliar application at Feekes 10 growth stage would be economical on Cu-deficient soils. However, Robson and Reuter (1981) found a poor relationship between Cu concentration in whole shoots sampled from tillering/branching to maturity and degree of Cu deficiency in plants. They suggested that sampling the youngest fully emerged leaf (YFEL) rather than whole plant shoots (WP) can greatly reduce the compounding effects of Cu accumulation in older leaves and

4 608 CANADIAN JOURNAL OF PLANT SCIENCE Table 3. Concentration of Cu (mg Cu kg -1 of dry weight) in the youngest fully emerged leaves (YFEL) of eight spring wheat cultivars sampled at different growth stages at Stony Plain, Alberta, in 1990 (prepared from Solberg et al. 1996) Growth stage (Zadoks scale) z Cultivar GS 12 G S 22 GS 24 GS 25 GS 39 Katepwa 9.11a 6.01a 5.30a 4.00a 3.49ab Roblin 8.01b 4.88c 4.30b 2.71de 2.25c Park 7.45b 5.18bc 3.95b 3.03cde 2.17c Laura 7.76b 5.23bc 4.11b 3.22bcd 2.80bc Conway 7.86b 5.55abc 4.41bc 3.75ab 2.77bc Oslo 9.01a 5.28bc 3.93b 2.60c 2.07c Columbus 8.84a 5.85ab 4.31b 3.34bc 2.70bc Biggar 7.97b 5.26bc 4.43b 3.40abc 3.90a Mean LSD z GS 12 Two leaf stage with 3rd leaf visible; GS 22 4th leaf emerged with 2nd tiller appeared; GS 24 4th leaf with four tillers developed; GS 25 5th leaf stage with 4 tillers; GS 39 5th leaf and boot formed. a e The values in each column separately are significantly different at P 0.05, when not followed by the same letter. Table 4. Copper concentration (mg Cu kg -1 ) in whole plant (WP) and youngest fully emerged leaf (YFEL) of barley at mid-tiller (GS 25) to stem elongation (GS 39) from Cu-responsive and non-responsive sites (prepared from Solberg et al. 1996) Cu-responsive sites Non-responsive sites DTPA-extractable DTPA-extractable Cu in soil YFEL WP Cu in soil YFEL WP Site (mg Cu kg 1 ) Cu +Cu Cu +Cu (mg Cu kg 1 ) Cu +Cu Cu +Cu Mean change in Cu concentration as plants aged. Based on correlation coefficients for seed yield vs. Cu concentration in plant tissue using Mitscherlich type function, other researchers have also suggested that analysis of young leaves for Cu concentration is a more sensitive diagnosis for Cu deficiency than whole plants (Graham and Nambiar 1981; Karamanos et al. 2004). Similarly, a comparison of Cu concentration between YFEL and WP of barley from Cu-responsive and non-responsive sites in Alberta showed greater differentiation using YFEL (3.8 vs. 5.9 mg Cu kg 1 for Cu-responsive and non-responsive sites, respectively) than WP (3.0 vs. 3.3 mg Cu kg 1 for Cu-responsive and non-responsive sites, respectively) (Solberg et al. 1996; Table 4). However, neither YFEL nor WP showed differences in tissue Cu concentration in response to Cu fertilization, suggesting that YFEL could not overcome the problem of changing Cu concentration with plant age. This agrees with earlier findings by Karamanos et al. (1986), who indicated that diagnosis of Cu deficiency was more accurate via soil than plant tissue analysis. Overall, tissue testing using whole plants was not reliable to diagnose Cu deficiency in crop. Neither the YFEL nor the WP showed differences in Cu concentration in response to Cu fertilization. Analyzing the YFEL improved the reliability of tissue tests, but it did not overcome the problem of changing Cu concentration with plant growth stage. CORRECTION OF COPPER DEFICIENCY Soil Application of Cu Seed yield response of a crop to Cu fertilizer remains the best way to define a deficient environment and is important in order to determine the amounts of Cu fertilizer needed for optimum seed yield in a particular soil type and/or climatic zone (Table 5). The severity of Cu deficiency in a crop varies with the level of available Cu in soil, crop species/cultivar, soil type and climatic conditions. Pre-seeding broadcast and incorporated Cu sulphate is generally considered more cost efficient because of its residual value and one-time application cost (Gartrell 1981). Incorporation of granular Cu fertilizer appears to be essential as broadcasting Cu fertilizer without incorporation has been found ineffective in increasing seed yield and Cu uptake of wheat on a Cu-deficient soil in Saskatchewan (Flaten 2002). In field studies conducted in the Prairie Provinces, seed yield of wheat increased with application of surface broadcast and incorporated Cu fertilizer, but the severity of Cu deficiency and magnitude of seed yield increase from applied Cu varied with the level of Cu in soil (Piening et al. 1987; Solberg et al. 1996; Karamanos et al. 2003). The amount of Cu required for optimum seed yield depends on the Cu fertilizer product being used and the method of application. In various field studies in the three Prairie Provinces by Karamanos et al. (1985, 1986, 2003, 2004) and Karamanos and Goh (2004), broadcast and incorporation of granular Cu sulphate (CuSO 4.5H 2 O) at kg Cu ha 1 or liquid Cu sulphonate at kg Cu ha 1 have produced maximum or near maximum seed yield of wheat. Compared with 4 kg Cu ha 1 rate, there was usually no significant increase in seed yield when granular Cu sulphate was applied at 8 kg Cu ha 1. Karamanos and Goh (2004) reported that near maximum yields were obtained with

5 MALHI AND KARAMANOS MANAGEMENT OF CU FERTILIZERS 609 Table 5. Seed yield response of wheat to broadcast and incorporation of different rates of granular Cu fertilizers on Cu-deficient soils (prepared from Solberg et al. 1996; Flaten 2002; Karamanos et al. 2005; Malhi et al. 2005) Reference Cu source Seed yield (kg ha 1 ) at Cu rates (kg Cu ha 1 ) Karamanos et al. (2005) Cu sulphate Flaten (2002) Cu sulphate Cu sulphate Malhi et al. (2005) Cu lignin sulphonate Solberg et al. (1996) Cu sulphate application of 2 kg Cu ha 1 and, furthermore, that application of rates as high as 10 kg Cu ha 1 as Cu sulphate resulted in yields lower than that of the control, perhaps indicating phytotoxicity at higher rates of Cu (Fig. 1). However, in a recent 3-yr study on a Cu-deficient soil in Saskatchewan, Malhi et al. (2005) found that soil incorporation of granular Cu fertilizers up to 2 kg Cu ha 1 did not produce any increase in seed yield and Cu uptake of wheat in the first 2 yr, and only became effective after the third annual application. The poor performance of these soil-incorporated Cu treatments might be due to the combined effect of the low rate of Cu fertilizer, the slow dissolution of Cu granules, and possibly the conversion of Cu in the soil to less available forms by adsorption, or other processes such as immobilization (Jones and Belling 1967; Norvell 1991). The effectiveness of soil broadcast-incorporated granular Cu fertilizer is also related to soil type and weather conditions. Under good moisture conditions, spring broadcastincorporated application of Cu fertilizer at 3 to 5.6 kg Cu ha 1 rates can provide adequate amounts of available Cu to most plants for optimum growth. In years with adequate moisture, roots are able to explore a larger volume of soil for Cu uptake and it is possible that yield response to Cu fertilizer may be reduced (Solberg et al. 1996). In an earlier study in Alberta by Malhi et al. (1989), wheat seed yield increase from Cu application on the surface followed by incorporation was much less with granular compared with solution Cu fertilizer. However, in another study in Alberta, seed yield of wheat was similar for soil broadcast-incorporated granular Cu sulphate at 3.3 kg Cu ha 1 and solution Cu chelate broadcast/sprayed on the surface followed by incorporation at only 1.1 kg Cu ha 1 (Solberg et al. 1996). This suggests that the availability of Cu is greatly affected by the low dispersion/dissolution properties of granular forms of Cu fertilizers, especially when these Cu fertilizers are applied at low rates or granules are relatively large (Karamanos et al. 2005). When low rates of Cu are applied, even though Cu disperses from the granule, the concentration of Cu in proximity to the plant roots may not be sufficient for optimum plant growth. This also suggests Cu sulphate that the problem of dispersion and uniform distribution of Cu ions in the soil can be overcome by broadcast/spray application of solution Cu fertilizer on the soil surface and incorporated, but this aspect needs further investigation for a number of years. The effectiveness of a Cu source depends on its solubility in water, which in turn affects the amount of available Cu for plant uptake and its method of placement (Table 6). Copper sulphate (bluestone, CuSO 4 5H 2 O) has been the most common Cu fertilizer used to correct Cu deficiencies under field conditions, owing to its high water solubility, relatively low cost and wide availability (Mortvedt 1991). It is normally broadcast and incorporated in the soil at rates of 3.5 to 15 kg Cu ha 1 for maximum effectiveness (Martens and Westermann 1991). Copper oxysulphates are oxides of relatively low solubility that are partially acidulated with H 2 SO 4. These products have been developed to be more compatible with application equipment than Cu sulphate, which is corrosive to metal. Their degree of solubility, usually related to availability of Cu to the plants, is directly related to their degree of acidulation, which varies according to the manufacturer (Mortvedt 1991). The order of water solubility for four common Cu fertilizers is Cu sulphate > Cu oxysulphate (12% Cu) > Cu oxysulphate (20% Cu) > Cu oxysulphate (10% Cu) (Haderlein and Dowbenko 2001). In a growth chamber experiment with wheat using a Cu-deficient soil with 0.2 mg DTPAextractable Cu kg 1, Haderlein and Dowbenko (2001) reported that seed yield increased significantly over the zero-cu control with application of Cu sulphate, Cu oxysulphate (12% Cu) and Cu oxysulphate (10% Cu), but the increase in seed yield with Cu oxysulphate (20% Cu) was not significant. Uptake of Cu in plant at maturity was significantly greater with Cu sulphate and Cu oxysulphate (12% Cu) than Cu oxysulphate (10% Cu) or Cu oxysulphate (20% Cu). Compared with the zero-cu control, Cu sulphate and Cu oxysulphate (12% Cu) had significantly greater uptake of Cu in plant, but there was little or no increase in Cu uptake with Cu oxysulphate (10% Cu) or Cu oxysulphate (20% Cu). The results verified that the solubil-

6 610 CANADIAN JOURNAL OF PLANT SCIENCE Fig. 1. Yield increase of wheat for deficient (, DTPA-Cu <0.4 mg kg 1 ) and sufficient (, DTPA-Cu >0.4 mg kg 1 ) soils (source: Karamanos and Goh 2004). ity of Cu products is linked to Cu uptake and plant yield. In Alberta, Micromate 155, a low solubility oxysulphate, was found less effective than Cu sulphate, particularly in the first year (Solberg et al. 1996). This effect was attributed to both the larger sized granules and low solubility of this Cu source. In a study in Saskatchewan, Malhi et al. (2005) reported that Cu sulphate and Cu lignosulphonate were more effective in increasing seed yield and Cu uptake of wheat than less-soluble Cu oxysulphate after second and third annual applications when all products were soil-incorporated at up to 2 kg Cu ha 1. In a review of western Canadian micronutrient fertilizer practices, Karamanos (2000) concluded that oxysulphates with solubility in water of less than 50% were generally inefficient in the year of application and recommended their application in the autumn preceding growing a Cu-sensitive crop. In a Saskatchewan field study on sandy loam to loamy sand soils, broadcast and incorporated Cu sulphate crystals at 5 kg Cu ha 1 were effective both in the year of application and the following year (Karamanos et al. 1986). However, Cu oxide granules were ineffective in the year of application, but became effective in the following year. Similarly, in another study in Saskatchewan, Cu sulphate at 5.6 or 11.2 kg Cu ha 1 gave a substantial increase in seed yield and Cu uptake of wheat compared with zero-cu control, while Cu oxide had little or no effect on seed yield in the application year (Flaten 2002). In a study in Alberta, Penney et al. (1993) also showed that broadcast and incorporated Cu oxide was less effective than Cu sulphate in enhancing yield of wheat, especially in the year of application. For economic and other reasons, there has been great interest in Cu fertilizer application methods (e.g., sidebanding, seedrow-placement or foliar application) that use low rates of Cu and also can be used under direct seeding. In Saskatchewan, seedrow-placed granular Cu fertilizers at the rate of 1.0 kg Cu ha 1 did not correct Cu deficiency in wheat even after three annual applications (Malhi et al. 2005). In Alberta, Solberg et al. (1996) obtained significant increase in seed yield of wheat from seedrow-placed granular Cu sulphate but at the 3.3 kg Cu ha 1 rate compared with 1.1 kg Cu ha 1 rate. Other studies in the Prairie Provinces have shown that seedrow-placed or sidebanded Cu was less effective than soil-incorporated or foliar-applied Cu (Malhi et al. 1989; Haderlein and Dowbenko 2001; Karamanos et al. 2004, 2005). Malhi et al. (2005) reported that seedrowplaced granular Cu fertilizers applied up to 1 kg Cu ha 1 were not effective in any of the 3 yr. This is in agreement with Karamanos et al. (2005) who established a 3-yr experiment to ascertain whether annual seedrow-placed Cu rates of either sulphate or chelated fertilizer forms (0, 1 and 2 kg Cu ha 1 ) in combination with foliar applications would provide an alternative long-term practice to simply broadcasting and incorporating Cu sulphate. They concluded that there is no agronomic or economic benefit from seedrow placement of granular Cu products and supplementing the Cu needs with a foliar Cu application, as all benefits arose from the latter; broadcasting and incorporation of 4 kg ha 1

7 MALHI AND KARAMANOS MANAGEMENT OF CU FERTILIZERS 611 Table 6. Effect of Cu sources on seed yield of wheat on Cu-deficient soils (prepared from Flaten 2002; Karamanos et al. 2004; Malhi et al. 2005) Rate of Cu Reference Method of application (kg Cu ha 1 ) Seed yield (kg ha 1 ) from different Cu sources Karamanos et al. (2004) Oxysulphate Ammonium sulphate + Cu Cu chelate First year Seedrow-placed Broadcast-incorporated Cu sulphate Cumulative after four annual applications Seedrow-placed Broadcast-incorporated Cu sulphate Flaten et al. (2002) Cu sulphate Cu oxide Broadcast-incorporated Broadcast Malhi et al. (2005) Cu lignin Cu Cu Cu Control sulphonate sulphate oxysulphate A oxysulphate B Broadcast-incorporated 2.0 Yr Yr Yr Seedrow-placed 1.0 Yr Yr Yr Foliar flag-leaf 0.25 Yr Yr Yr

8 612 CANADIAN JOURNAL OF PLANT SCIENCE as Cu sulphate provided maximum yields. This suggested that seedrow placement of Cu does not provide enough feeding sites for the growing roots of crops due to the great distance between fertilizer granules. Gilkes and Sadleir (1979) suggested that the ability of a root to take up Cu is limited to distances of less than 2 cm when using Cu superphosphate in a very Cu deficient sandy soil (0.4 mg total Cu kg 1 ). To attain maximum benefit from soil-applied granular Cu fertilizers, dispersion and uniform distribution of Cu from granules has to be rapid enough to supply all Cu needed by the plant in an early crop growth stage. Hence, Cu fertilizers should be surface broadcast and incorporated into soil well in advance of seeding. The study by Karamanos et al. (2005) provided a statistically significant grain yield increase only in 3 of 10 site-years from seedrow/foliar application and only when the Cu fertilizer was in sulphate or chelated forms. However, yield increases thus obtained were neither economical nor as good as those obtained with broadcast and incorporated Cu sulphate. Further, compared with a single, 4-yr-old broadcasting and incorporation of 4 kg Cu ha 1, the authors demonstrated that residual effects of seedrow-applied Cu at rates up to 4 kg ha 1 were very small and were obtained primarily after 3 yr of annual applications and with sulphate or chelated products only. Based on the results of a laboratory study using soil leaching columns, Flaten et al. (2003) suggested that seedrow application of granular Cu fertilizers may not be effective due to sporadic placement of granules at low rates and lack of mobility of Cu from granules to the roots. The poor performance of seedrow-placed or sidebanded Cu fertilizers due to limited accessibility and availability of Cu or limited mobility in the soil band of application in relation to plant root growth area is also supported by the work of McLaren et al. (1983). Other researchers (Jones and Belling 1967; Gilkes and Sadlier 1979) have reported that Cu was highly immobile in the soil and it was only available to wheat roots within a 2- cm zone of placement. Gilkes (1977) suggested that limited contact between roots and Cu fertilizer may result when granules of Cu fertilizer are applied in a band. Moreover, seedrow-placed Cu fertilizer can occasionally result in reduced plant stand (Solberg et al. 1996), likely due to its toxic effect (Robson and Reuter 1981). Residual Cu in Soil Although Cu fertilizers are expensive, they can remain effective for several years, thus, the long-term residual effect should be determined. Many researchers have observed residual effects of Cu fertilizer on crop yield (Pizer et al. 1966; Caldwell 1971; Gartrell 1980, 1981; Karamanos et al. 1986). In Australia, single soil application of Cu sulphate at kg Cu ha 1 was found to increase crop yield for yr. The amount of available Cu in soil tends to increase with time from multi-year annual or high initial Cu applications (Solberg et al. 1996; Malhi et al. 2005; Karamanos et al. 2005; Table 7). Therefore, Cu fertilizers applied at high initial rates are expected to produce residual effect on plant-available Cu in soil and subsequently on seed yield and quality for a number of years. The residual yield benefit to future crops from high initial Cu fertilizer application may occur due to carry-over of residual Cu in soil and from the release of Cu from decomposing crop residues. In a field study in Alberta, residual effect of Cu chelate was evident 4 yr after single application at 3 kg Cu ha 1 (Malhi et al. 1989; Table 8). In Alberta, Karamanos et al. (2005) reported similar residual seed yield response for 5 yr from single application of granular Cu sulphate at 4 kg Cu ha 1 to wheat. In another field study in Alberta, Solberg et al. (1996) obtained residual responses from single application of Cu fertilizers for up to 6 yr, and the seed yield increases were similar for soil broadcastincorporated granular Cu sulphate at 3.3 kg Cu ha 1 and solution Cu chelate broadcast/sprayed on surface followed by incorporation at 1.1 kg Cu ha 1. Single applications of Cu sulphate have been shown to provide residual benefits for 5, 12 or even 100 yr (Gartrell 1981; Martens and Westermann 1991). The benefit of this method is sometimes increased in the year following application, and then sustained for many years (Gartrell 1980, 1981). This is most likely due to further dispersion/dissolution of Cu ions into the soil, resulting in increased accessibility of Cu to crop roots and uptake of Cu. Foliar Application of Cu Foliar treatments to date have been considered an emergency method for in-crop use when Cu deficiency is detected after seeding. Sulphate, oxide or chelate of Cu in water solution can be applied to the growing crop. Davies et al. (1971) found a similar increase in grain yield of wheat from soil incorporated and foliar applied Cu fertilizer. In other experiments, where soil test levels were not severely deficient, foliar treatments were as effective as broadcast and incorporated Cu sulphate, but were much more effective than seedrow-placed Cu fertilizers (Karamanos 2000). Foliar applications at 0.20 to 0.25 kg Cu ha 1 applied at the Feekes 6 growth stage appear to provide a solution to Cu deficiency when identified during the growing season (Karamanos et al. 2004). Malhi et al. (2005) also demonstrated that foliar application at 0.25 kg Cu ha 1 at flag-leaf resulted in wheat seed yield increases of %. Further, the nitrogen use efficiency (NUE) increased to kg grain kg 1 N with the N + Cu application compared with kg grain kg 1 N with application of N alone. The performance of foliar application is dependent on the time of application in the growing season and environmental conditions (Graham 1976; Karamanos et al. 1986, 2004; Penney et al. 1993; Solberg et al. 1996; Malhi et al. 2005; Table 9). Foliar applications at middle growth stages are more effective than at very early or very late growth stages (Graham 1976; Miller et al.1994; Solberg et al. 1996; Karamanos et al. 2004). In a field study in Manitoba where foliar applications of Cu fertilizer on wheat were made at Feekes 2 (4-leaf ), Feekes 6 and Feekes 10 (flag-leaf) growth stages (Large 1954), seed yield increase was 121, 302 and 216 kg ha 1, respectively (Karamanos et al. 2004). In this study, maximum seed yield in some instances was obtained with dual foliar applications, one at Feekes 6 and the other at Feekes 10.

9 MALHI AND KARAMANOS MANAGEMENT OF CU FERTILIZERS 613 Table 7. Amount or concentration of DTPA-extractable Cu in soil (0-15 cm) after annual or initial Cu applications to wheat with different sources, rates, times and methods of Cu fertilizer in Saskatchewan and Alberta (prepared from Solberg et al. 1996; Karamanos et al. 2005; Malhi et al. 2005) Rate of Cu Cu Cu Method of application (kg Cu ha 1 ) Cu chelate Cu sulphate oxysulphate I oxysulphate II Amount of Cu (kg Cu ha 1 ) in soil after four annual applications at Porcupine Plain, SK (Malhi et al. 2005) Granular Broadcast-incorporated Seedrow-placed Broadcast-incorporated Seedrow-placed Solution Cu Cu Cu Cu chelate sequestered I sulphate/chelate sequestered II Foliar 4-leaf Foliar flag-leaf Concentration of Cu (mg Cu ha 1 ) in soil (Solberg et al. 1996) Millet, AB Legal, AB Stony Plain, AB 1 yr z 5 yr 1 yr 5 yr 2 yr 6 yr Broadcast-incorporated (Cu sulphate) Foliar Micro Mate Concentration of Cu (mg Cu ha 1 ) in soil (Karamanos et al. 2005) Average of all Cu rates and products after 5 yr y 0 15 cm cm 0 30 cm No Cu Seedrow-placed Broadcast-incorporated z Refers to years after one-time initial Cu fertilizer application. y Cu oxysulphate, EDTA, or sulphate were seedrow applied annually for 4 yr at 1, 2 and 4 kg Cu ha 1 ; Cu sulphate was broadcast and incorporated once in the first year at 1, 2 and 4 kg Cu ha 1. Table 8. Residual effect of copper chelate applied at 3 kg Cu ha -1 in 1984, on stem melanosis incidence and seed yield of Park wheat grown in 1985 to 1987 on a Cu-deficient Black Chernozemic sandy loam soil at Lacombe, Alberta soil (prepared from Malhi et al. 1989) Percent disease Seed yield (kg ha 1 ) Treatment Cu Cu + Zn Cu + NPK Cu + Zn + NPK Zn Zn + NPK NPK Control LSD In a 3-yr study in Saskatchewan, Malhi et al. (2005) reported that in-crop foliar application of Cu at flag-leaf (Feekes 10) resulted in substantial increase in seed yield and Cu uptake, while foliar application at four-leaf (Feekes 2) did not give any consistent increase in seed yield of wheat. In a study in Alberta, Solberg et al. (1996) obtained substantial seed yield increase in wheat from foliar application at late boot (one-fourth of head out) growth stage, while lesser seed yield increase occurred when foliar application was made after all heads were fully emerged. The results suggest that in-crop foliar applications can be beneficial as a rescue operation to restore seed yield, but every effort

10 614 CANADIAN JOURNAL OF PLANT SCIENCE Table 9. Effect of time of foliar application of Cu fertilizers ( kg Cu ha 1 ) on seed yield of wheat on Cu-deficient soils (prepared from Solberg et al. 1996; Karamanos 2004; Malhi et al. 2005) Reference Cu source Seed yield (kg ha 1 ) with foliar-applied Cu at different growth stages Malhi et al Control Cu at 4-leaf Cu at flag leaf Cu chelate yr Cu chelate yr Cu chelate yr Solberg et al. Control Late-boot Heading 1996 z Cu chelate Cu sulphate Karamanos et al. Control Feekes 6 Feekes 6 and y Feekes Control Cu citric acid z Late boot refers to growth stage when one-fourth of the heads were out and heading refers to when all heads were out. y Feekes 2, Fekes 6 and Fekes 10 growth stages refer to beginning of tillering, beginning of stem elongation and sheath of last leaf completely out, respectively. should be made to prevent Cu deficiency in the growing season in order to get maximum yield by making most efficient use of other fertilizer nutrients and soil water. Time of application in the growing season can be a factor in determining the effect of Cu fertilization on different plant parts. For example, under severe Cu stress seed yield can not be maximized when Cu fertilizer is applied only once at a very late growth stage, because much of the applied Cu may accumulate in the leaves without translocation to the seed (Solberg et al. 1996; Karamanos et al. 2004). Like seed yield, dry matter yield was also influenced by the time of Cu application (Malhi et al. 2005). Overall, both soil and foliar applications were effective to overcome Cu deficiencies in crops, although soil applications (at relatively much higher rates compared with foliar) were superior (Table 10). SENSITIVITY OF CROP SPECIES/CULTIVARS TO COPPER DEFICIENCY Crop species vary in their sensitivity to Cu deficiency, cereals being more sensitive than other crops. Based on the results of a field study in Alberta, Solberg et al. (1996) found that wheat and barley were equally the most sensitive to Cu deficiency, while lesser responses were observed with oats and no responses with canola. Karamanos et al. (1986), however, showed that although canola and flax were less responsive to applied Cu than cereals, significant yield increases could be obtained from these crop species through Cu fertilization in severely deficient soils in Saskatchewan, though flax was much more responsive than canola. McAndrew et al. (1984) reported that, among cereal crops, wheat was the most sensitive to Cu deficiency. Similarly, Smilde and Henkens (1967) reported that sensitivity to Cu deficiency was generally greatest in wheat, lowest in oats and intermediate in barley. Furthermore, differences in Cu deficiency sensitivity have been reported among cultivars within the various cereal crops species (Nambiar 1976; Piening et al. 1989; Solberg et al. 1996). In some instances, these differences may be as great as the differences from one crop species to another (Nambiar 1976). INTERACTION OF COPPER WITH OTHER NUTRIENTS Growth and seed production of wheat have been shown to be affected by nutrient imbalances in soil (Touchton et al. 1980). Increasing supply of P, N and Zn can increase severity of Cu deficiency in crops (Touchton et al. 1980; Gartell 1981; Graham and Nambiar 1981). High levels of P, Zn, Fe, Mn and Al in soil can restrict Cu absorption by plant roots and induce Cu deficiency in crop plants, and high level of N in soil can delay the translocation of Cu in crop plants. Graham and Nambiar (1981) stated that application of N alone to a situation of mild Cu deficiency (absence of visual Cu deficiency symptoms) resulted in severe Cu deficiency symptoms and loss of seed yield. This was most likely due to delay in translocation of Cu from older leaves to new leaves, thus enhancing the severity of Cu deficiency. In Alberta, Malhi et al. (1989) also reported that application of Cu and N together resulted in large increase in seed yield compared with N alone. Researchers have also shown that increasing the supply of certain nutrients in soil, due to the introduction of legumes in the cropping system (Graham and Nambiar 1981) or because of the application of manure to the soils, may increase the severity of Cu deficiency by creating a nutrient imbalance in soil or by reducing the amount of available Cu in soil due to increased complexing of Cu by organic matter (Graham and Nambiar 1981; Solberg et al. 1996). Interactions of Cu with other nutrients can be a result of competition for the same uptake mechanism (Kausar et al. 1976) or soil reaction, e.g., due to displacement of Cu 2+ from specific adsorption sites on colloids with Zn 2+ and vice

11 MALHI AND KARAMANOS MANAGEMENT OF CU FERTILIZERS 615 Table 10. Effect of method of application on seed yield of wheat on Cu-deficient soils (prepared from Flaten 2002; Karamanos et al. 2004, 2005; Malhi et al. 1989, 2005) Reference Cu source Rate (kg Cu ha 1 ) Seed yield (kg ha 1 ) with different placement methods Karamanos et al. (2005) Control Broadcast-incorporated Sidebanded Seedrow-placed Cu sulphate 4.0 yr z yr yr yr yr-5 y Broadcast-incorporated Seedrow-placed Foliar flag-leaf Malhi et al. (2005) Control (2.0 kg Cu ha 1 ) (1.0 kg Cu ha 1 ) (0.25 kg Cu ha 1 ) Cu lignosulphonate yr yr yr Karamanos et al. (2004) Broadcast- incorporated Foliar Feekes 6 Feekes 6 + Feekes 6 + Control (4.0 kg Cu ha 1 ) (0.22 kg Cu ha 1 ) Feekes 10 Feekes 6 + soil Feekes 10 + soil Cu sulphate Karamanos et al. (2005) Seedrow-placed x kg Cu ha kg Cu ha 1 Cu sulphate Cu lignosulphonate 0.22 Plus Foliar Malhi et al. (1989) Solution Granular Control broadcast-incorporated sidebanded Foliar Cu chelate Cu sulphate Flaten (2002) Broadcast-incorporated Seedrow-placed Foliar Feekes 6 Foliar Feekes 10 Control (5.6 kg Cu ha 1 ) (1.1 kg Cu ha 1 ) (0.28 kg Cu ha 1 ) (0.28 kg Cu ha 1 ) Cu sulphate Karamanos et al. (2005) Control Broadcast Broadcast Seedrow-placed Foliar Feekes 10 (5.6 kg Cu ha 1 ) 11.2 kg Cu ha 1 ) (1.1 kg Cu ha 1 ) (0.28 kg Cu ha 1 ) Cu sulphate z Average of control for three placement treatments. y Residual effect only in year 5. x Third year of a 3-yr experiment with annual seedrow application of Cu.

12 616 CANADIAN JOURNAL OF PLANT SCIENCE versa (Loneragan 1975). Karamanos et al. (1985a, 1991) demonstrated the importance of proper balance between manganese (Mn) and Cu for nutrition of wheat and barley working with organic soils in Saskatchewan. Maximum yields were only achieved when the DTPA-extractable (1:5 soil:extractant ratio) Mn:Cu ratio of organic soil was in the range of for barley and 1-15 for wheat. Further, Karamanos et al. (1989) observed an interaction of Cu with S and Mo with canola in a growth chamber experiment, thus confirming the need for balanced nutrition. In Alberta, application of 12.2 kg P ha 1 increased the yield of barley on Cu-deficient soils only when Cu was applied (Penney et al. 1993), and exceedingly high P application rates (217 kg P ha 1 ) were required to induce a Cu deficiency in an Alberta soil with DTPA Cu extractable level of 0.35 mg kg 1 (Lee 1992). COPPER DEFICIENCY AND CROP DISEASES Deficiency of Cu is often associated with stem melanosis of wheat (Hooper and Davies 1968; Graham and Nambiar 1981; Alloway and Tills 1984). This disease generally occurs in irregular patches, associated with browning discoloration of rachis in wheat caused by Pseudomonas cichorii (Tsuchiya et al. 1980). Poor lignification has been postulated as a factor in the lack of resistance in Cu-deficient plants (Bussler 1981). The globular exudates of soluble carbohydrates from the stems of senescing Cu-deficient plants may also encourage the development of stem and head melanosis (Graham 1980). In the Canadian prairies, spring wheat (Triticum aestivum L. em Thell Park ) grown on Cu-deficient soils was found highly susceptible to stem melanosis caused by Pseudomonas cichorii (Swingle) Stapp (Piening and MacPherson 1985), and was effectively controlled by the application of Cu (Piening et al. 1987; Malhi et al. 1989; Tables 11 and 12). In a study with three cereals (wheat, barley and oats), wheat was the only cereal found to exhibit stem melanosis (Piening et al. 1987). In this study, seed yield loss from this pathogen depended on the cultivar of wheat grown, Park having the most disease. Piening et al. (1987) demonstrated that stem melanosis of Park and other wheat cultivars was significantly mitigated when the Cu-deficient soil was amended with Cu chelate at 2 or 4 kg Cu ha 1. Incidences of other diseases of wheat such as take-all (caused by Gaeumannomyces graminis), powdery mildew [caused by Blumeria graminis (DC) E.O. Speer f. spl. Tritici syn. Erisiphe graminis CC f. sp. tritici] and ergot [caused by Claviceps purpurea (Fr.:Fr.) Tul] have been reduced when Cu was added to deficient soils (Wood and Robson 1984; Graham 1980; Solberg et al. 1996). Wilting of leaves in alfalfa has also been induced by Cu deficiency in soil (Tremblay et al. 1999). Table 11. Comparisons of six wheat cultivars for stem melanosis severity and seed yield with and without added copper in a field experiment on a Black Chernozemic sandy loam soil at Lacombe, Alberta in 1985 (prepared from Piening et al. 1989) Disease severity (%) Seed yield (kg ha 1 ) Without Cu With Cu Without Cu With Cu Park Neepawa Sinton Thatcher Columbus Katepawa SUMMARY, CONCLUSIONS AND FUTURE RESEARCH NEEDS Prevention and/or correction of Cu deficiency in crops on Cu-deficient soils has a dramatic effect on seed yield and quality of cereals, especially wheat and occasionally yield increases up to 400% were observed with Cu fertilization. Source, rate, formulation, time and method of Cu application, and proper balancing of Cu with P, Mn, N or other nutrients in soil all affect seed yield of wheat on Cu-deficient soils. Where Cu deficiency in soil is expected in advance, seed yields are usually optimized with broadcast/incorporation application of granular Cu fertilizers at kg Cu ha 1 at seeding on most soils. Soil incorporation of granular Cu fertilizers up to 2.0 kg Cu ha 1 was not generally effective in increasing seed yield of wheat in the year of application, but it became effective after three annual applications. Surface-broadcast application of granular Cu fertilizers without incorporation was much less effective in preventing Cu deficiency and improving seed yield of wheat than incorporated Cu fertilizers. Compared with granular Cu fertilizers, surface spray broadcast application followed by incorporation of solution Cu fertilizers into the soil at 0.5 to 2.0 kg Cu ha 1 was found to be much more effective in preventing Cu deficiency and increasing wheat seed yield in the year of application. Seedrow-placed Cu affords neither agronomically nor economically acceptable yield increase. The findings also suggest that seed dressing or banding is not a desirable method of application for Cu fertilizers, because it reduces availability of Cu to plant roots due to poor distribution of granules with low rates of Cu fertilizer. Some Cu fertilizers (e.g., Cu oxide) were not effective in increasing seed yield in the year of application, and were still generally less effective than other fertilizers even after a series of annual applications. Soil application at relatively high rates produced residual benefits for a number of years. If Cu deficiency in wheat appears during the growing season, foliar application of Cu fertilizer at low rates (about kg Cu ha 1 ) between late tillering and flag-leaf can be used to correct Cu deficiency and restore seed yield considerably. But foliar applications at very early or very late growth stages were not effective or were much less effective. In some cases on soils with extreme Cu deficiency, two foliar applications (one at late tillering or first node formation and the other at flag-leaf or boot stage) of Cu fertilizer or a combination of both soil and foliar applications were found to produce maximum seed yield. Application of Cu fertilizers to wheat on Cu-deficient soils improved seed quality (kernel plumpness, hectoliter weight, 1000-kernel weight and concentration of Cu in seed), but there was no noticeable effect on protein concentration in seed. The increase in concentration and uptake of