PLACEMENT OF PHOSPHORUS AND NITROGEN FERTILIZERS FOR MINIMUM TILL CORN UNDER SPRINKLER IRRIGATION ((ZEA MAYS L.), NO-TILL, EFFICIENCY)

Three maize (Zea mays L.) experiments were established in 1983 and 1984 to evaluate the effectiveness of various methods and sources of nitrogen (N) and phosphorus (P) in a reduced-till sprinkler irrigation practice. Phosphorus method-source studies were conducted on a calcareous soil at Loup City, NE and an acid soil at Mead, NE. Dual placed (DP) N and P in a localized band (anhydrous ammonia applied with liquid P sources) increased P uptake and corn grain yields on a calcareous soil as compared to P banded to the side of the seed (BS) and banded below the seed (BB). Broadcast preplant (BRP) applications were equally as effective as DP methods under reduced tillage practices. Explanation of enhanced DP yields and P uptake could lie in the synergistic effect of N and P placed together, especially when the ammoniacal form of N is used. Urea phosphate (UP) provided greater yields and total P uptake in both the grain and stover as compared to P sources ammonium polyphosphate (APP) and diammonium phosphate (DAP) at the calcareous soil site. The greater early uptake of P when BB and BS did not increase grain yield and or P uptake versus DP and BRP methods of P placement. Anhydrous ammonia injected preplant and or sidedress provided superior yields and uptake efficiencies when compared to all other sources of N used (sulfur coated urea, urea ureaphosphate, urea and urea ammoniumnitrate). Data suggest that N sources should be placed below the soil surface in reduced-tillage practices to prevent microbial immobilization and volatilization losses. Nitrogen from ear-leaf tissue samples (analyzed for total-N) that were taken at early silking was highly correlated with yield. Results of ear-leaf analysis might be used to recommend the amount of N to be applied through irrigation during grain fill. Tissue samples were taken throughout the growth cycle of maize and analyzed for phosphate phosphorus (dilute acetic acid extractable) and total phosphorus (nitric-perchloric acid digestion). High correlation was found between the results of these two procedures, indicating that one method is as good as the other for assessing the relative P status of the plant. The dilute acid extractable measurement can also be used to predict total P uptake by the plant