Effects of phosphorus application method and rate on furrow-irrigated ridge-tilled grain sorghum

Conservation tillage systems, including ridge-tillage, have become increasing popular with producers in the central Great Plains because of their effectiveness in controlling soil erosion and conserving water. A major disadvantage of the ridge system is that nutrient placement options are limited by lack of any primary tillage options. The objective of this research was to investigate the effects of method of phosphorus (P) placement and rate on irrigated grain sorghum [Sorghum bicolor (L.) Moench] grown in a ridge-tillage system on a soil low in available P. This experiment was conducted from 1993 to 1995 on a producer's field near the North Central Kansas Experiment Field at Scandia, Kansas on a Carr sandy loam soil (course, loamy, mixed, calcareous, mesic, Typic Udifuvents). Treatments consisted of fertilizer application methods, surface broadcast, single band starter (5 cm to the side and 5 cm below seed), dual band starter (one band on each side of the row), and knifed in the center of the row middle (38 cm from each adjacent row). Each of these treatments was made at either 22 or 44 kg P2O5 ha-1, and nitrogen (N) also was included at the rate of 13 kg ha-1. Additional treatments were, a combination of 13 kg N and 44 kg P2O5 ha-1 applied half broadcast and half as a single band starter, a 1:1 N:P2O5 ratio (44 kg N and 44 kg P2O5 ha-1) applied as a single band starter and a 3:1 ratio (134 kg N and 44 kg P2O5 ha-1) applied as a single band starter. A no-P check plot also was included. Broadcast and center-of-row middle knife applications were made approximately 1 week before planting. After planting, N was balanced on all plots to give a total of 180 kg ha-1. Applied P treatments improved grain yield and nutrient uptake and consistently shortened the time from emergence to mid-bloom on all 3 years of the experiment. On this low soil test P soil, treatments that subsurface banded P increased grain yield by 1.27 Mg ha-1 compared to broadcast treatments. Placing N and P in a single starter band 5 cm to the side and 5 cm below the seed was as effective as placing a band on each side of the row. Knife applying N and P in the center of the row was not as effective as placement below the row. Single band starter application of N and P in a 1:1 and or 3:1 N:P2O5 ratio consistently increased yields and nutrient uptake and shortened the time to mid-bloom as compared to the single band starter treatment that provided only 13 kg N ha-1. Over the 3 years of the study, these 1:1 and 3:1 N:P2O5 ratio starters were clearly superior to an other treatments.