Submitted to: International Conference on Site Specific Agriculture
Publication Type: Proceedings
Publication Acceptance Date: July 19, 2000
Publication Date: N/A
Interpretive Summary: Improved efficiency of crop production requires matching crop varieties to soil conditions. Extraction of soil samples with ion-exchange resin permits us to obtain a measure of several elements in a single extraction. By matching seed yield with soil chemical properties we can identify a) varieties that will grow well on the soil, b) potentially toxic elements, and c) fertilizer practices that will enhance crop yield. These facts were demonstrated in a field study with three soybean varieties. Soil samples taken from the study site were extracted and the results for several elements were compared with soybean seed yields. One soybean variety, 9061, was sensitive to the presence of vanadium (a rather toxic element) and to the vanadium:vanadium+phosphorus ratio. A second soybean variety, 9091, was sensitive to the ratio of magnesium:magnesium+calcium. A third variety, 704, was sensitive to the same factors as variety 9061 plus the resin extractable phosphorus concentration. Gains in yield of 20% or more were observed within the field for sites with the best element ratios. Greenhouse studies suggest that magnesium would be an economical fertilizer for variety 9091. The results point to two important observations. Banding magnesium or phosphorus might be the best means of fertilizing soil when complex effects are observed. The northwestern Cornbelt is an area within which both corn and soybean yields are depressed by the presence of vanadium. In these soils, crop yields can be improved by selecting varieties and hybrids that are unaffected by vanadium.
Technical Abstract: Plant growth is sensitive to concentrations of resin extractable elements in soil. Resin extractable element concentrations vary with soil type, landscape position and climatological zone. We have shown that soybean (Glycine max L.) seed yield is sensitive to the resin extractable V:(V+P) molar ratio in soil and that the effect of this ratio was cultivar-dependent. Because V is a potent ATPase inhibitor and Mg and Ca are important ATPase cofactors, we examined the data for correlation between seed yield and the resin extractable Mg:(Mg+Ca) molar ratio. Data were obtained from a 3.2 ha field site. The field site was divided into three equal portions and each had 360 plots. Two cultivars were planted in 1995 (9091 and 9061) and a third (704) was added in 1996 and 1997. Composite soil samples were taken from 180 plots in each portion to a depth of 60 cm. Surface soil samples (6 g) from selected plots were subjected to oextraction with cation and anion resin extractors for 5 days. Extractors were washed and eluted with acid and the extracts were analyzed with ICP methods. Seed yields of 9091 increased by 27% as the resin extractable Mg:(Mg + Ca) molar ratio increased 0.2 to 0.8. Seed yields of 9061 increased in 2 of 3 years as the Mg:(Mg + Ca) molar ratio increased. Seed yields of 704 increased as the resin extractable Mg:(Mg + Ca) molar ratio increased in both years in which it was grown. The relative gains of 9061 and 704 were much less than those of 9091. Greenhouse studies using the same soils as the field study show soybean yields are increased with the application of MgPO4; this suggests a real effect of resin extractable Mg on soybean yields. Knowledge of complex elemental interactions serves as a guide to both site specific soil management and plant breeding.