STARTER FERTILIZER EFFECTS ON GRAIN-SORGHUM HYBRIDS GROWN ON A SOIL HIGH IN RESIDUAL PHOSPHORUS IN A NO-TILLAGE ENVIRONMENT

Conservation tillage crop production systems have become common in the central Great Plains because they reduce soil erosion and increase wa ter-use efficiency. The high residue levels associated with no-tillage systems can cause soils to be cool and wet which can reduce nutrient uptake and growth of crops. Starter fertilizer applications have been effective in improving nutrient uptake even on soils high in available nutrient elements. Resent research indicates that corn (Zea mays L.) hybrids differ in their responses to starter fertilizer. No informatio n is currently available concerning grain sorghum [Sorghum bicolor (L. ) Moench] hybrid response to starter fertilizer. The objective of this study was to evaluate grain sorghum hybrid responses to starter ferti lizer in a no-tillage environment on a soil high in available phosphor us (P). This field experiment was conducted from 1995 to 1997 at the N orth Central Kansas Experiment Field, located near Belleville, on a Cr ete silt loam soil (fine, montmorillonitic, mesic, Pachic Arguistoll). Treatments consisted of 12 grain sorghum hybrids and two starter fert ilizer treatments. Fertilizer treatments were starter fertilizer [34 k g nitrogen (N) and 34 kg P2O5 ha(-1)] or no starter fertilizer. Starte r fertilizer was applied 5 cm to the side and 5 cm below the seed at p lanting. Immediately after planting, N was balanced on all plots to gi ve a total of 168 kg N ha(-1). In all three years of the experiment, g rain yield, total P uptake (grain plus stover), grain moisture content at harvest, and days to mid-bloom were affected by a hybrid x starter fertilizer interaction. Starter fertilizer consistently increased yie lds, reduced harvest grain moisture, improved total P uptake, and redu ced the number of days needed from emergence to mid-bloom of Pioneer 8 505, Pioneer 8522Y, Pioneer 8310, Dekalb 40Y, Dekalb 48, Dekalb 51, De kalb 55, and Northrup King 524, but had no effect on Pioneer 8699, Dek alb 39Y, Northrup King 383Y, and Northrup King 735. When averaged over the three years, starter fertilizer increased grain yield of respondi ng hybrids (hybrids in which the 3-year average grain yield was signif icantly increased by the application of starter fertilizer) by 920 kg ha(-1). In responding hybrids, starter fertilizer reduced grain moistu re at harvest by 54 g kg(-1) and also shortened the period from emerge nce to mid-bloom by five days. Starter fertilizer increased V6 stage a boveground dry matter production and N and P uptake of all hybrids tes ted. Results of this work show that in high residue production systems even on soils high in available P, starter fertilizer can consistentl y increase yield of some hybrids, whereas other hybrids are not affect ed.