Micronutrient Status in Dairy Farms of Uruguay Etat des micronutriments dans les fermes laitières d'uruguay

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1 Scientific registration n : 2162 Symposium n : 14 Presentation : Poster Micronutrient Status in Dairy Farms of Uruguay Etat des micronutriments dans les fermes laitières d'uruguay MORON Alejandro (1), BAETHGEN Walter E. (2) (1) INIA La Estanzuela, Colonia, Uruguay, moron@inia.org.uy (2) IFDC Latin America, Montevideo, Uruguay, baethgen@undp.org.uy INTRODUCTION Crop and pasture production in Uruguay is typically limited by soil nitrogen (N) and phosphorus (P) availability. Dairy production systems include pastures (grasses and legumes) in rotation with annual crops (maize, oats, wheat, etc.). Due to biologically fixed N by legumes P has traditionally been considered the most common limiting nutrient for pasture production. However, recent evidences suggest that this situation has changed (Mor n and Baethgen, 1996a, 1996b). These authors conducted a survey of maize fields in dairy farms and found that the vast majority of the fields showed insufficient plant N content levels due to low rates of applied N fertilizer and common lack of N fertilizer split applications. The survey also revealed frequent deficiencies of potassium (K) and sulfur (S), and no general limitations in other macronutrients. No information is available in Uruguay on the micronutrient status of maize fields in dairy farms. However, micronutrient deficiencies can be expected in the dairy production regions of Uruguay due to the following reasons. Dairy production has become much more intensive in the last two decades which has resulted in higher yields, higher soil nutrient extraction through animal products (milk and beef), as well as nutrient transfer in the animal excreta to non productive areas such as milking parlors, roads, etc. Intensive dairy systems are partially based on hay and silage production which also imply high net nutrient losses from the soil. Also, typical fertilizers used in Uruguayan dairy farms are triple superphosphate (TSP), diammonium phosphate (DAP) and NP bulk blends. These used fertilizer sources and the fact that modern fertilizers have less impurities has resulted in no application of micronutrients. The objective of our research was to survey the nutritional status of maize crops in dairy farms of Uruguay with respect to iron (Fe), manganese (Mn), copper (Cu), molybdenum (Mo), boron (B) and zinc (Zn). 1

2 MATERIALS AND METHODS Plant (maize for silage) and soil samples were taken from a 14 dairy farms of two major dairy production areas of Uruguay (southern and western regions) during two growing seasons: 1993/1994 and 1994/1995. No information is available in Uruguay on micronutrient sufficiency ranges () for maize. Therefore, our plant nutrient content results were compared to maize as published by Mills and Jones (1996) (Table 1). The critical level is the lower limit of the sufficiency range below which nutrient deficiency occurs. Table 1. Sufficiency ranges () for iron (Fe), manganese (Mn), copper (Cu), molybdenum (Mo), boron (B) and zinc (Zn) in ear leaf of maize at silking (mg of nutrient per kg dry matter of plant tissue). Micronutrient (mg/kg) Fe 2-25 Mn 2-2 Cu 6-2 Mo B 5-25 Zn 25-1 Plant and soil samples were taken when approximately 5% of the maize plants were at the silking growth stage. General information was obtained for each field regarding crop and soil management practices including previous crops, tillage systems, fertilizer use, etc. Plant samples from each field consisted of 2 replications of 3 leaves (first leaf immediately below the spike), which were dried at 65 o C and ground. The following standard methods were used to determine micronutrient content in the laboratory: Cu, Fe, Mn and Zn with nitro-perchloric digestion and atomic absorption spectrophotometry; B by dry ashing and colorimetry with azomethine-h; and Mo by dry ashing followed by inducted coupled plasma (ICP). Most soils in the surveyed region are Mollisols, Vertisols and Alfisols. Two composite soil samples (15 cores) were taken at -2 cm depth in each field: one came from the maize row and the other one from the interrow space. Samples were analyzed to: organic carbon; available P by Bray I and cationic exchange resins (Zamuz and Castro, 1974); exchangeable K (extracted with ammonium acetate and determined by flame photometry); soil ph in water (soil solution ratio 1:2.5). Soil texture (scale USDA) was determined by sieving the sand fractions and with hydrometer for clay and silt. The following laboratory analyses were performed for analyzing micronutrient soil content: labile forms of Cu, Fe, Mn and Zn by extraction with DPTA-TEA buffered at ph 7.3 and atomic absorption spectrophotometry; available B by extraction with BaCl 2 in microwave oven and colorimetric determination with azomethine-h. 2

3 RESULTS AND DISCUSSION We found large variability in the chemical and physical characteristics of the soils included in the survey. Mean values (and ranges) for soil properties were: ph in water 5.9 ( ); organic C 21 g/kg (7-46); Bray I P 18 mg/kg (3-78); resin P 28 mg/kg (3-242); exchangeable K.5 cmol(+)/kg (.1-1.2); clay content 273 g/kg (2-46); silt content 36 g/kg (11-63); sand content 367 g/kg (11-84). Regarding plant analyses, no maize fields showed deficient levels of Fe, B and Mn and only very few sites had deficient Mo values. Moreover, most of the sites presented values for these micronutrients which were well above the critical levels (Figures 1, 2, 3 and 4). Approximately 1% of the surveyed fields presented deficient plant Cu and about 15% were above but close to the critical level of 6 mg/kg content (Figure 5). The most frequent deficiency in the surveyed fields was found for Zn: more than 2% of the fields showed maize content below the sufficiency range, and approximately an additional 2% were near the critical Zn level (Figure 6). The relatively high proportion of low Zn content values found in our survey is especially important considering that maize is highly sensitive to Zn deficiency (Jones; 1991; Martens and Westermann, 1991). Interpretation of the micronutrient status of the surveyed fields can change if other nutritional guides were used for selecting sufficiency ranges (e.g., Cornforth, 1984; Malavolta et al., 1989; 1997; Jones et al., 1991; van Raij et al., 1996; Reuter and Robinson, 1997). The largest changes in the interpretation of the sufficiency ranges would occur by applying the Brazilian nutritional guides (van Raij et al., 1996; Malavolta et al., 1989; 1997) to our B and Zn results. Thus, if these authors critical levels (1 and 15 mg B/kg, respectively) were used, the percent maize fields with B deficiency would increase to 2% and 7%, respectively (Figure 2). On the other hand, if the Brazilian critical level for Zn content (15 mg/kg) was applied to our results no Zn deficiencies would be found (Figure 6). These results evidence the need for establishing sufficiency ranges for Uruguayan conditions. The soil analyses for micronutrient content showed very poor relationship with the corresponding plant tests (data not shown). A weak association was found for Zn and B soil and plant analyses which justifies further studies. The general poor association between micronutrient soil and plant analyses may be partially due to the fact that our study was based on a survey and not on field experiments. Farmer field surveys include several factors which may present confounding effects (i.e., different soil types, 3

4 Figure 1. Ear leaf Fe content of maize Figure 2. Ear leaf B content of maize Fe (mg/kg) B (mg/kg) Mn (mg/kg) Figure 3. Ear leaf Mn content of maize Mo (mg/kg) Figure 4. Ear leaf Mo content of maize Figura 5. Ear leaf Cu content of maize Figure 6. Ear leaf Zn content of maize Cu (mg/kg) Zn (mg/kg) previous management practices, maize cultivars, tillage systems, etc.). In spite of this limitation some trends were found in our study which agree with other published results (Martens and Westermann, 1991; Mills and Jones, 1996). For example lower Zn and Mn maize content values were observed in soils with higher ph. Also, fields with very high soil P values showed medium or low plant Zn content. 4

5 CONCLUSIONS 1. Our results evidence the need to establish micronutrient sufficiency ranges for maize in Uruguayan conditions, as well as improving and/or developing more appropriate soil indices. 2. The survey also suggests that initial research efforts in Uruguay should be concentrated in Zn > B > Cu. REFERENCES Cornforth, I.S Plant Analysis. In: Cornforth, I.S. & Sinclair, A.G., compiled. Fertiliser and lime recommendations for pasture and crops in New Zealand. Ministry of Agriculture & Fisheries. Second Revised Edition. p Jones, J.B Plant analysis in micronutrients. In: Mortvedt, J. J., ed. Micronutrients in agriculture. Second Edition. SSSA. Madison. Chapter 12. p Jones, J. B. ; Wolf, B.; Mills, H.A Plant analysis handbook. Micro - Macro Publishing, Inc. 213 p. Malavolta, E.; Vitti, G. C.; De Oliveira, S.A Avaliaçao do estado nutricional das plantas. principios e aplicaçoes. Associaçao Brasilerira para Pesquisa da Potassa e do Fosfato. Piracicaba-SP. 21 p. Malavolta, E.; Vitti, G. C.; De Oliveira, S.A Avaliaçao do estado nutricional das plantas. principios e aplicaçoes. 2 ediçao. Associaçao Brasilerira para Pesquisa da Potassa e do Fosfato. Piracicaba-SP. 319 p. Martens, D.C. ; Westermann, D.T Fertilizer applications for correcting micronutrients deficiencies. In: Mortvedt, J. J., ed. Micronutrients in agriculture. Second Edition. SSSA. Madison. Chapter 15. p Mills, H. A.; Jones, J. B Plant analysis handbook II. Micro - Macro Publishing, Inc. 422 p. Moron, A.; Baethgen W. 1996a. Relevamiento de la fertilidad de los suelos bajo produccion lechera en Uruguay. Serie técnica 73. INIA. Uruguay. 16 p. Moron, A.; Baethgen W. 1996b. Relevamiento de la fertilidad de los suelos bajo produccion lechera en Uruguay. XIII Congresso Latinoamericano de Ciência do Solo. çguas de Lindoia, SP-Brasil CD Rom. Reuter, D.J.; Robinson, J.B Plant analysis: an interpretation manual. 2nd ed.csiro Publishing. 536 p. van Raij, B. ; Cantarella, H.; Quaggio, J.A.; Furlani, A.M.C Recomendaçaoes de adubaçao e calagem para o Estado de S o Paulo. Boletim Técnico 1. 2 ed.campinas. Instituto Agron mico- Fundaçao IAC. 285 p. Zamuz, E.M. de & Castro, J.L Evaluacion de métodos de analisis de suelo para determinar fosforo asimilable. La Estanzuela, Centro de Investigaciones Agr colas "Alberto Boerger", 15 p. (Bolet n Técnico 15). Keywords : micronutrients, maize, Fe, Cu, Mn, B, Zn, Mo, dairy farms Mots clés : micronutriments, maïs, Fe, Cu, Mn, B, Zn, Mo, fermes laitières 5