Keywords: hydroponic, media, soilless culture, zeolite

Transcription

1 EXPLORING THE POSSIBILITY OF USING A ZEOPONIC-BASED MEDIUM FOR NUTRIENT MANAGEMENT OF GREENHOUSE TOMATOES 1 Richard G. Snyder, Boyett Graves, and Arthur Bufogle Mississippi State University P.O. Box 231, Crystal Springs, MS U.S.A. Abstract: A zeoponic-based medium was compared to other media in a spring crop of greenhouse tomatoes. Fruit yield and quality, as well as fruit chemistry, leachate chemistry, and tissue analysis were recorded and analyzed. A zeoponic/pine bark blend produced marketable yield similar to rockwool and perlite. However, zeoponic treatments without added nutrient solution produced lower total and marketable yield, and were deficient in several nutrients. Keywords: hydroponic, media, soilless culture, zeolite Introduction A spring 1997 crop of greenhouse tomatoes was grown to evaluate a new zeoponic-based medium, and to compare it to other conventional soilless media being used by this industry in the U.S. Clinoptilolite is a form of zeolite, a soilless, lightweight mineral with a high cation exchange capacity. It is designed to have desirable physical properties for a container medium, while also serving as a substrate for controlled release of selected plant nutrients. The intention of utilizing this product is to attempt to reduce the total fertilizer needs of a crop, as well as the volume of nutrient solution applied. Fruit yield and quality, as well as nutritional data were collected to determine how this medium would perform. Materials And Methods Tomato plants of the variety 'Blitz' were seeded 9 November 1996, and transplanted 9 January 1997 into Greenhouse #2 at the Truck Crops Experiment Station, Crystal Springs, MS. This is a relatively new indeterminate Dutch hybrid beefsteak type variety from De Ruiter Seeds. Treatments were as follows: 1) Zls 50% + pine bark 50%; with season-long nutrient solution; 2) Z3 25% + pine bark 75%; with seasonlong nutrient solution; 3) Z3 50% + pine bark 50%; with season-long nutrient solution; 4) Z3 25% + pine bark 75%; water only, no added nutrients; 5) Z3 50% + pine bark 50%; water only, no added nutrients; 6) 100% pine bark with nutrient solution (control); 7) 100% rock wool aggregate with nutrient solution (control); 8) 100% perlite with nutrient solution (control). Treatment number 6 represents the standard method of production for growers in Mississippi: composted pine bark fines (< 3 /s inch diameter). Treatments 7 and 8 are more representative of most multiacre producers in the U.S. No additional fertilizer solution was used in treatments 4 and 5, since these were tests to determine if enough nutrient value for the entire crop could be pre-charged into the Z3 media; plants in these plots received only water. All treatments were fed and/or watered automatically utilizing electronic time clocks, injectors, and drip irrigation to each plant. All treatments received the same amount of solution at each application. All media were mixed and placed in 2 cubic foot polyethylene bags in early January. 1 This research was supported by a grant from ZeoponiX, Inc. and Boulder Innovative Technologies, Inc., as a NASA subcontract. 138

2 Each plot consisted of 16 plants growing in 4 lay flat bags of the designated media (4 plants per bag). The experimental design was a randomized complete block, with 3 replications. Prior to planting, three replicate samples of each medium were analyzed at the Mississippi State University Soil Testing Laboratory. This included ph, total soluble salts (TSS), and percent organic matter, as well as extractable nutrient levels of phosphorus, potassium, calcium, magnesium, zinc, and sulfur. Total cation exchange capacity and percent base saturation for H, K, Ca, and Mg was determined as well. Following termination of this crop, an additional set of samples were analyzed. Leachate samples were collected weekly, and volume, electroconductivity, and ph were recorded. These samples were drawn from polyethylene-lined troughs which captured all leachate from bags. Fruit were harvested twice each week (Monday and Thursday), and separated into quality grades. Fruit counts and weights were recorded. Marketable fruit were considered to conform to USDA standards for U.S. no. 1 tomato fruit. Culls were fruit which were not marketable, either due to physiological disorders, damage, shape, or size. Mean fruit size was determined by dividing marketable weight by marketable number. When fruit were harvested from the fourth cluster, laboratory analysis of leaf tissue for N, P, K, Ca, Mg, S, Fe, Mn, B, Cu, and Zn was performed. At that time, leachate was analyzed for P0 4, K, Ca, Mg, S, Na, Fe, Mn, Cu, Zn, and B. Also, fruit were tested for ph, total acidity, Brix, vitamin C, and fruit color. The crop was be terminated 10 June. Statistical analysis was performed on all data with analysis of variance, and mean separations by Duncan's New Multiple Range Test. Results & Discussion Foliage in treatment 4 began showing visual nitrogen deficiency symptoms (general yellowing of the leaves) within four weeks after transplanting. Treatment 5 followed with these symptoms two weeks later, although the symptoms were still less pronounced than in treatment 4 at the end of April. This deficiency was anticipated to lead to lower yields over the life of the crop. Plants in other treatments appeared to have normal green foliage, with no noticeable differences among treatments. Treatments 3 and 7 produced the highest number of marketable fruit, significantly more than treatments 4 and 5 (Table 1). Treatments 3 and 7 were not significantly different from each other. Other treatments were intermediate in yield. This indicates that the 50/50 mixture of Z3 with pine bark was comparable to a pure rockwool aggregate growing medium. However, when the daily nutrient solution was not used (4 and 5) marketable number dropped. Treatment 4 (25% Z3) produced a significantly lower yield than treatment 5 (50% Z3), which had a larger total amount of initial fertilizer charge. Treatments 3 and 7 were the top marketable weight producers, in addition to treatment 8, the perlite grown plants. Treatments 3, 7, and 8 were not significantly different from each other. These produced higher weights of marketable fruit than treatments 4 and 5 (those without nutrient solution). Treatment 4 was significantly lower than treatment 5 in marketable weight (Table 1). Treatment 4 had significantly lower weight and number of cull grade fruit than the other treatments. This may be because there were not marketable, culls, and total fruit (Table 1). At the end of the experiment, all remaining green fruit were harvested to determine if there was a difference in crop maturity at the termination date. A large number of green fruit remaining would indicate slower maturity. Treatment 7 had the highest green fruit number remaining, while treatment 4 had the least. This appears to show that fruit lingered on plants grown in rook wool, while they matured more quickly from the 25% Z3 plants. However, it more likely is a reflection of a higher total fruit load from the former and a lower total load from the latter. Treatments 2,7, and 8 had the highest total green fruit weights, while treatment 4 had the lowest. Total yield data show that treatments 4 and 5 produced less fruit than all other treatments, both in terms of fruit number and fruit weight. Treatment 4 (25% Z3) yielded less than treatment 5 (50% Z3) in both cases, again suggesting that treatment 4 was the most deficient in fertilizer. However treatment 5 139

3 -Q jo >- 0) «150 - a> 100 jro Figure 1. Cumulative Yield of Media Treatments in ZeoponiX Experiment 50%Z1s+50%PB+Nutr.Sol. 25%Z3+75%PB+Nutr.Sol. 50%Z3+50%PB+Nutr.Sol. 25%Z3+75%PB+Water 50%Z3+50%PB+Water Pine Bark+Nutr.Sol. Rock Wool+Nutr.Sol. Perlite+Nutr.Sol. I 50 < o Sampling Date (month/day) appears to have suffered from lack of fertilizer during the growing season as well. A plot of cumulative total yield over time for the eight treatments is shown in Figure 1. Marketable fruit from treatments 2 and 8 were significantly larger than fruit from treatments 3,4, and 5. Fruit from treatment 4 were the smallest (7.7 oz.). Mean fruit size was close to 8 ounces. Fruit quality, measured as percentage marketable fruit by weight, was highest in treatment 3 and lowest in treatments 4 and 5. Fruit quality was lower than normal for all treatments, due primarily to irregular ripening. This physiological disorder is believed to be due to an unexpected population of silverleaf whitefly (Bemisia argentifolii) which injects a toxin into plants. This toxin interferes with ripening. This is a fairly recent development in greenhouse tomatoes. Because of the poor fruit quality towards the end of the crop, it was terminated about 2 weeks earlier than usual for a spring crop. At the time when plants were being harvested from the fourth cluster, fruit were collected for chemical analysis. Three marketable fruit from each plot, in 3 replications, were collected for analysis at the Mississippi State University Food Technology Laboratory. The three fruit per plot were blended together and subjected to tests for brightness (L), redness (a), and yellowness (b) of the fruit surface, as well as ph, total sugars (Brix), and total acidity in fruit (as citric acid). In addition, fruit from treatments 1, 3, 6, and 7 were tested for ascorbic acid (vitamin C) content, in three replications. There were no significant differences found in any of these variables (data not presented). Prior to planting, three replicate samples of each growing medium were collected and submitted to the Mississippi State University Soil Testing Laboratory for analysis. Total soluble salts (TSS) and organic matter content (%OM) were measured, and extractable levels of P, K, Ca, Mg, Zn, and S were determined. This was repeated after the experiment was terminated (10 June). All variables were highly significantly different in the testing before and after the experiment. Plots of extractable P, K, Ca, Mg, Zn and total soluble salts, before and after the experiment, are included in Figure 2a-f. Leaf samples, consisting of the youngest, fully expanded leaves from 12 plants per plot, were taken for tissue analysis when the plants reached the stage of yielding fruit from the fourth cluster. These were analyzed at the Mississippi State University Tissue Analysis Laboratory. Treatments 4 and 5 had significantly lower levels of nitrogen than all other treatments. Treatment 4 (with 25% Z3) was lower than treatment 5 (with 50% Z3). Both of these treatments would be considered to be deficient in nitrogen at the 140 \

4 time of this test (less than 4%), and this was also detected visually. Treatment 7 (rock wool) was highest in leaf potassium content, and treatments 4 and 5 were the lowest. Other treatments were at intermediate levels. Treatments 4 and 5 were deficient in potassium (substantially less than 4%). The depressed nitrogen and potassium levels in leaf tissue of treatments 4 and 5 would account for the premature yellowing of leaves mentioned under visual observations. Leachate was collected from one bag in each plot once per week. Electroconductivity (EC), ph, and total volume were recorded weekly. Data were analyzed over all dates. ph of the leachate was highest for treatments 4 and 5, averaging a little over 7.0. This level is higher than recommended for greenhouse tomatoes in aggregate media. Treatment 3 had the lowest average ph (6.02), with other treatments intermediate in value. All values were between 6.0 and 7.2. Optimum ph of nutrient solution for greenhouse tomatoes is in the range of 5.6 to 5.8. There were large numerical differences in leachate EC. Treatments 4 and 5 averaged EC lower than 0.2, which indicates almost pure water effluent from the bags. This is due to the lack of daily nutrient solution being applied to these treatments. The EC of leachate from all other treatments ranged from 1.5 to 2.2, which is fairly close to the EC of the nutrient solution applied. In open feeding systems, such is this one, the effluent EC is normally close in value to the applied solution EC. The volume of water in the effluent was significantly greater from treatments 4 and 5 than from all other treatments, perhaps because these plants were smaller and consequently transpired less water than the larger plants in other treatments. These were the two treatments which received only water. At the time when plants yielded fruit at the fourth cluster, leachate was collected for chemical analysis. This testing was performed on an ICP-3000 Analyzer Spectrophotometer (Leco Instruments). Calcium, potassium, magnesium, sodium, phosphorus, copper, iron, manganese, and zinc concentration in the leachate were measured. All elements were significantly different among treatments. Calcium was highest in treatment 1, and lowest in treatments 4 and 5. The higher level in treatment 1 is likely due to higher calcium levels in the Z1 formulation of zeoponic than in Z3 or other media. Potassium was highest in the leachate from treatments 6, 7, and 8, and lowest in treatments 4 and 5. The latter two treatments did not receive daily nutrient solution, so would be expected to have less potassium in the leachate. Other treatments were intermediate in value. Overall, treatments 4 and 5 had the lowest levels of elements in the leachate. Assuming that the nutrient composition of leachate reflects that of solution in the root zone, the elemental levels were indicative of nutrient starvation for all elements for these two treatments. Conclusions Treatments 3, 7, and 8 had the highest marketable yield. Treatments 1, 2, 3, 6, 7, and 8 were similar in most respects in regards to yield and quality. Treatments 4 and 5 had lower yield and quality, with treatment 4 not performing as well as treatment 5. Also, marketable fruit from treatment 4 were the smallest in average fruit size. There were no differences among treatments in any of the fruit chemistry characteristics (brightness (L), redness (a), or yellowness (b) of the fruit surface, ph, total sugars (Brix), total acidity in fruit (as citric acid), or ascorbic acid (vitamin C) content. Treatments 4 and 5 were deficient in nitrogen, potassium, iron, and copper, as determined by leaf tissue analysis at the time of fourth cluster set. While treatments 4 and 5 appeared to be unsuitable for producing greenhouse tomatoes due to inadequate fertilizer reserves during the growing season, treatment 3 with 50% Z3 had enhanced yield (marketable number and weight) when compared with some other treatments. When used with daily nutrient solution, this growing medium was acceptable. There may very well be a blend of Z3 and pine bark higher than 50% Z3 which could substitute for daily supplements of nutrient solution. However, this would need to be determined in future experiments. Alternatively, a formulation of Z3 which could retain fertilizer over a longer period of time would be more suitable for a long term crop, such as tomatoes. The current formulation of Z3 might work well with a shorter term crop such as potted ornamentals. 141

5 Table 1. Effects of Media Treatments on Yield and Quality Greenhouse Tomato Fruit. 2 Treatment y %Z %PB Mkt. No." Mkt. Wt.(lbs) Cull No. Cull Wt.(lbs) Green No. Green Wt. (lbs) Total No. Total Wt.(lbs) Fruit Size (oz.) % Mkt (Wt) 1) AB 98AB 312A 118A 14AB 5.1AB 513A 220A 8.39AB 45.6BC 2) AB 99 AB 299A 122 A 17AB 6.5A 501A 227A 8.59A 45.2BC 3) A 125A 273A 102A 15AB 5.6AB 534A 232A 8.13B 55.OA 4) C 41C 209B 55B 2C 0.7C 297C 96C 7.67C 42.9C 5) B 74B 278A 97A 6BC 2.3BC 431B 174B 8.08B 43.0C 6) 100 PB 186AB 97AB 316A 116A 14AB 5.5AB 516A 218A 8.34AB 45.5BC 7) 100 RW 216A 112A 281A 109 A 19A 7.1A 516A 228A 8.28AB 50.6AB 8) 100 PER 200AB 106A 291A 118A 17AB 6.6A 508A 231A 8.47A 47.1BC significance" ** ** ** ** * * ** ** ** * z Values are means of 3 replications; each replication consists of 16 plants; harvested biweekly. y %Z=%Z 3 or Z1; %PB=% pine bark; Treatment 1 used Zl; all other Z treatments used Z3; treatments 4 and 5 received water in place of nutrient solution. x *=statistically significant at 0.05 level; ** =statistically significant at 0.01 level; NS = not statistically significant at the 0.05 level; means within a column followed by the same letter are not statistically significantly different by Duncan's New Multiple Range Test.

6 Figure 2. Extractable nutrient levels for growing media before and after experiment. i^m Before Exp. mil After Exp. vp O m + V) N O LO o O CO eo CO C/3 CO CO O O CM CM z z z z z z CM CM X X X X + + o a) CQ CQ CQ m CO p Q_ 0- Q. CQ CQ Q_ a. m V NP ^ CD o N 0. Q. ^ LO a) a. O o _c LO ID \P o^ o LO \P o^ r-- to N- O LO + + CO CO Li- o w co a: N CO + + N CO CO N N N ^ gs N N vp NP o^ o^ LO o Vp LO O o CM to LO o CM LO LO CM m Treatment CO W CO z z z o CO p izz CQ a) CD 0- C o CL o a: 143