Fertilizer Placement Effects on Seasonal Nitrogen Accumulation and Yield of No‐Tillage and Conventional Tillage Sorghum

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Abstract
Little information is available concerning fertilizer placement effects on accumulation of fertilizer N in no‐tillage sorghum [Sorghum bicolor (L.) Moench]. Possible differential accumulation patterns among tillage systems could influence management practices for these systems. Fertilizer N placement effects on sorghum yield and N accumulation in 1985 and 1986 were evaluated in a field study on a Weswood silt loam soil (fine‐silty, mixed, thermic Fluventic Ustochrept) near College Station, TX. Four N rates (0, 50, 100, and 150 kg N ha−1) as NH4NO3 were surface broadcast or subsurface banded into soil managed with no‐tillage or conventional tillage. Nitrogen‐15‐depleted NH4NO3 was applied to microplots receiving the 150 kg N ha−1 rate to monitor plant fertilizer N accumulation with seasonal progression. Fertilizer and total (fertilizer plus soil) N accumulation patterns were the same for both no‐tillage and conventional tillage treatments. Total N accumulation at harvest, and grain and stover yields were higher with banded placement. Leaf N concentration at anthesis indicated better N nutrition in banded treatments. Most total and fertilizer N accumulation had occurred by anthesis both years, with most of the N allocated to stover. During grain filling, the panicle became the primary N sink. Placement influenced neither total nor fertilizer N accumulation at anthesis in 1985, but these parameters were higher for banded treatments by harvest. Fertilizer N accumulation in culms and leaves early in the 1986 season was higher in broadcast treatments. At harvest, more total N had accumulated in broadcast treatment panicles, but more fertilizer N had accumulated in banded treatment panicles. Fertilizer uptake patterns indicated subsurface band placement was the most effective method of supplying fertilizer N for both tillage treatments.