No-Tillage Grain Sorghum Response to Starter Nitrogen-Phosphorus Combinations

The use of starter fertilizers has become common in conservation-tillage corn (Zeu mays L.) production systems, but little attention has been given to starter fertilizer nutrient ratios for no-tilled grain sorghum [Sorghum bicolor (L.) Moench]. The objective of this study was to evaluate the effect of N:P starter fertilizer ratios on no-tillage grain sorghum production at two planting dates. This field experiment was conducted from 1991 through 1993 at the North Central Kansas Experiment Field, located near Belleville, on a Crete silt loam soil (fine, montmorillioitic, mesic, Pachic, Argiustoll). Treatments included combinations of N and P to supply 0, 10, 30, or 90 lb N/acre with or without 13 lb P/acre. An unfertilized check plot and a broadcast treatment receiving 90 lb N and 13 lb P/acre (nostarter check) also were included. Planting dates were mid-May and mid-June each year. All starter treatments were applied 2 in. to the side and 2 in. below the seed at planting. Immediately after planting, broadcast surface applications were made to bring the total amount of fertilizer applied on all plots, except the unfertilized check, to 90 lb N and 13 lb P/acre. Only the treatments that included either 30 or 90 lb N/acre with 13 lb P/acre (2.81:1 or 6.92:1 N:P ratios) consistently improved early-season growth, plant tissue P uptake, and yield of grain sorghum over the 90 lb N and 13 lb P/acre broadcast treatment. When averaged over the 3 yr, the starter combinations that included either 90 or 90 lb N with 13 lb P/acre shortened the time from emergence to mid-bloom and increased yield by 18% over the no-starter check. These yield increases were consistent for both planting dates. Results of this work demonstrate that grain sorghum growth and yield can be improved with starter fertilizer applied in either a 2.31:1 ratio (30 lb N and 13 lb P/acre) or 6.92:1 ratio (90 lb N and 13 lb P) rather than a 0.77:1 ratio (10 lb N and 13 lb P/acre) for grain sorghum grown in the central Great Plains. Research QuestionNo-tillage systems have proven to be effective in reducing soil erosion, however, large amounts of surface residues found in no-tillage systems can adversely affect early-season growth, nutrient uptake, and yield of crops. Starter fertilizers have proven beneficial in no-tillage corn. Their use and formulation for grain sorghum in the central Great Plains has not been evaluated, however. Grain sorghum can be planted over a wide range of dates. Little information is available on grain sorghum response to starter fertilizer at either an early or a late planting date. The objective of this research was to evaluate no-tillage grain sorghum response to various N-P combinations applied as a starter fertilizer at two planting dates. Literature SummaryIn some experiments that have evaluated corn response to N-P starter fertilizers, improved early growth and yield increase were attributed to the P component. Other studies have found that N is the most critical element in the combination on soils that are not low in available P. Some researchers have found that when P was banded, N also had to be included in the band for stimulation of P uptake. At some locations, the ratio of N to P was critical for yield response to starter fertilizer, but at other sites no agronomic differences were found with N:P ratios of 0.77:1, 2.31:1, or 6.92:1. Several studies have demonstrated the benefits of starter fertilizer for no-tillage corn, but little information is available on response of no-tillage grain sorghum to starter fertilizer N-P ratios. Study DescriptionThis research was conducted from 1991 to 1993 at the North Central Kansas Experiment Field, near Belleville, on a Crete silt loam soil. Soil test P (Bray-1) level was in the medium range. Treatments consisted of planting dates (mid May and late June) and liquid N-P starter fertilizer combinations to supply 0, 10, 30 or 90 lb N/acre with or without 13 lb P/acre. An unfertilized check plot and a broadcast treatment receiving 90 lb N/acre and 13 lb P/acre (no-starter broadcast check) also were included. Starter fertilizer treatments were knife-applied at planting in a band 2 in. to the side and 2 in. below the seed. Immediately after planting, surface broadcast applications were made to all plots except the unfertilized check plots to bring the total amount of fertilizer applied to 90 lb N and 13 lb P/acre for all treatments. Applied QuestionHow did planting date and starter fertilizer N-P combinations affect early-season plant growth, P uptake, maturity, and yield of no-tillage grain sorghum? Starter fertilizer improved early-season growth and P uptake, hastened maturity, and increased yield of no-tillage grain sorghum when applied in the proper rate combinations (Table 1). Starter fertilizer in a traditional 0.77:1 N:P ratio (10 lb N/acre and 13 lb P/acre) did not prove to be as effective as a 2.31:1 (30 lb N/acre and 13 lb P/acre) or a 6.92:1 (90 lb N/acre and 13 lb P/acre) ratio. The 2.31 and 6.92 ratio fertilizers both increased grain yields by 18% over those with the broadcast check. These two treatments also reduced the number of days from emergence to mid-bloom by nearly a week. Nitrogen or P applied alone as a starter did not improve early growth or yield compared with the broadcast check treatment. Response to starter fertilizer was consistent for both ealry and late planting dates. Table 1Effect of starter fertilizer combinations (averaged over planting date and years) on early-season (6-leaf stage) dry matter production, P uptake, grain yield, and number of days from emergence to mid-bloom of grain sorghum. 6-Leaf stageStarterDry matterP uptakeGrain yieldDays to mid-bloom---- N, P, lb/acre ---------- lb/acre -----bu/acreFertilizer treatment†10135872.2 916630136772.61016090137012.71015990 05912.0 876630 05752.0 8766 0135802.0 88669013 broadcast5562.0 8366FLSD(0.05) 590.2 7 1†All treatments received balancing broadcast N and P to give 90 lb N and 13 lb P/acre.