Phosphorus and potassium placement for corn and soybean managed with two conservation tillage systems

Barker, Daniel
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Conservation tillage systems can maximize yields in the long term without compromising the quality of the soil for the future. The area of no-till systems in Iowa has decreased since 1995 for reasons difficult to explain. One reason may relate to uncertainty and expenses concerning P and K fertilizer management practices. This project assessed the effects of fertilization and placement of P and K on grain yield and early growth of corn and soybean in no-till and chisel till systems. Long term trials were established in 1994 at five Iowa State University research centers. Each location accommodated four separate but adjacent trials, one for each nutrient-crop combination. These were P and K trials for com and soybean. Treatments for each nutrientcrop combination were several combinations of four fertilization rates and three placements in no-till and chisel till systems. The chisel tillage produced larger plants early in the growing season for both crops and nutrients. Grain yield ofcom was responsive to tillage over sites and years by 187 kg ha-I with a 295-345 kg ha-I increase in grain yield at some locations. Soybean grain yield was not affected by tillage. Although there were no significant tillage by placement interactions, a significant tillage by fertilizer interaction showed that com yield increases due to applications of P fertilizer were higher for no-till at one location. Phosphorus fertilization increased early growth ofcom and soybean, especially when banded with the planter. Potassium fertilization and placement did not affect early growth ofeither crop. Grain yields of com and soybean were significantly greater when P or K fertilizers were applied at several locations. Com and soybean yields were seldom affected by P placement. Deep-band K produced higher com yields than other placements, even in high testing soils where no response was expected. There was no significant relationship between increases in early growth and greater grain yield for both crops. Stratification was largely reduced when deep-band P was applied but placement of K fertilizer did not reduce levels of stratification. In conclusion, early growth of both crops were greater in chisel till then for no-till. Chisel till usually produced greater com grain yield than no-till while tillage seldom affected soybean yield. Grain yield of both crops benefited from P or K fertilizer applications. Planter-band P was effective for increasing early growth ofcom and soybean. Deep-banded K increased com grain yield when compared to other placements even in some high testing soils.