Tillage, fertilizer application method, and N rate effects on utilization of depleted HN₄NO₃ by sorghum

Abstract

Effects of tillage and fertilizer placement and rate on sorghum (Sorghum bicolor L. Moench) yield and N accumulation in 1985 and 1986 were evaluated on a Weswood soil near College Station, Texas. Four N rates (0, 50, 100, & 150 kg N ha⁻¹) were surface broadcast or subsurface banded using no-tillage or conventional tillage. Labelled NH₄NO₃ was applied to microplots receiving the 150 kg N ha⁻¹ rate to monitor plant fertilizer accumulation. Soil samples were collected from microplots after harvest to quantify residual fertilizer. Leaf N concentration and leaf area index anthesis, grain and stover yield, and total N accumulation at harvest increased with increasing N rate. Curvilinear regressions typified relationships of leaf N and grain yield with applied N, while linear N relationships were typical for N accumulation and stover yield. Conventional tillage produced more grain and stover than no-tillage at low N rates. At higher rates, tillage differences were negligible. Leaf N concentration, total N accumulation, and grain and stover yields were higher with banded placement. Most total and fertilizer N accumulation occurred by anthesis and was primarily located in vegetative tissue, while later in the season N was translocated to the panicle. Early fertilizer accumulation tended to be higher with no-tillage. As the season progressed, mineralization provided soil N to no-tillage sorghum and differences in fertilizer accumulation declined, resulting in no yield difference due to tillage at 150 kg N ha⁻¹. Toward the end of the season, more fertilizer accumulation occurred in banded treatments, even though placement effects on yield were not significant at 150 kg N ha⁻¹. Most fertilizer recovery was from plant accumulation, with a small portion recovered from soil. More fertilizer was recovered from soil in broadcast treatments because less fertilizer uptake by sorghum occurred. Residual fertilizer recovery in banded treatments was primarily from the original band, but lateral movement did occur. Fertilizer recovery from broadcast treatments was primarily from the surface, indicating fertilizer immobilization.