Even though soybean [Glycine max (L.) Merr.] fixes N from the air, N demand at the R4 to R6 (pod‐fill) growth stages of high‐yielding, high‐protein soybean may be greater than the amountsss of available N with normal farming practices. In Kansas, supplemental N has not been recommended on soybean regardless of yield level. Research was conducted at eight sites over a 2‐yr period on irrigated soybean to evaluate effects of N rates (0, 20, 40 lb/acre) and sources (urea‐ammonium nitrate solution [UAN], ammonium nitrate, urea, urea + N‐[n‐butyl] thiophosphoric triamide NBPT]) on leaf N concentrations, grain yield, and grain protein, and oil concentrations. The NBPT used is a commercially available urease inhibitor. Most N was broadcast but UAN was applied over the top of the canopy through flat‐fan nozzles. All applications were made at the R3 growth stage. Nitrogen concentrations in leaf samples taken 2 to 3 wk after N application were unaffected by N fertilization. Soybean yields were increased significantly by late‐season N application at six of eight sites; the average increase was 6.9 bu/acre or 11.8 %. Both of the nonresponsive sites had yields averaging under 50 bu/acre, whereas responsive sites yielded 56 bu/acre or more. Soybean plants at all locations were well nodulated. In most cases, 20 lb N/acre provided positive responses. Late‐season N fertilization increased grain protein and oil concentrations at some sites, but overall combined analysis indicated nonsignificant effects. Nitrogen sources performed similarly. Application of UAN resulted in leaf burn, which probably reduced yields at the 40 lb N/acre rate. However, this would not be a problem for producers applying UAN through irrigation systems where the UAN would be much more diluted. Even when well nodulated, soybean with high yield potential may not be able to take in enough N to achieve maximum yield of high quality grain. Public and private soil test labs and crop consultants may have to reevaluate N recommendations for soybean with high yield potential. Supplemental N application at the R3 growth stage can provide positive economic returns for producers growing irrigated soybean with high yield potential. Research Question Can soybean symbiotically fix enough N to produce high yields under irrigation? Producers of irrigated soybeans are now routinely achieving yields in excess of 60 bu/acre. A soybean crop yielding 70 bu/acre requires nearly 250 lb N/acre. Late‐season supplemental N may increase yields. In addition, future soybean marketing strategies may include protein and oil concentrations. Late‐season supplemental N has potential to affect these seed quality considerations. The objective of this research was to evaluate the effects of late‐season supplemental N on soybean grain yield and composition. Literature Summary Previous research on N fertilization of soybean has produced inconsistent results. Much of the earlier work evaluated N applied either preplant, at planting time, or early in the growing season. Results from previous work in...

High residue levels provide excellent erosion control but can result in cool, wet seedbeds creating a situation where starter fertilizer may be beneficial. Research was conducted from 1999 to 2001 evaluating N rates in starter containing N, P, K, and sometimes S; and different starter fertilizer placements for continuous no‐till corn (Zea mays L.). Placements consisted of direct seed contact, dribble over‐the‐row, and a subsurface band (5 cm below and 5 cm to the side of the seed row). Nitrogen rates for direct seed and dribble placements were 11, 22, 45, and 56 kg N ha−1; and 34, 67, 101, and 134 kg N ha−1 for the subsurface placement. Nitrogen was balanced at 168 kg ha−1 on all treatments, including a no‐starter check using broadcast ammonium nitrate at planting. Addition of S in starter was evaluated with subsurface placement. Starter fertilizer, regardless of placement, often increased early season dry matter production and significantly increased grain yields. Increasing N above 22 kg ha−1 in direct seed contact did not increase yields and significantly reduced stands 2 of 3 yr. Stands were unaffected with higher N rates in dribble over‐the‐row and subsurface placements; however, applying N above 11 and 34 kg ha−1, respectively, resulted in little added yield benefit. Inclusion of 11 kg S ha−1 in a subsurface starter fertilizer sometimes increased early season dry matter production, grain yield, and nutrient uptake. Results suggest starter fertilizer is an effective, efficient way of stimulating early growth and improving yields of continuous no‐till corn in Kansas.

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Increasing acreage of no‐till (NT) cropping systems with surface applications of N fertilizer brings forth the important issue of management of acidic soils in these systems. Our objectives were to determine the vertical movement of surface‐applied lime, and to determine if frequency or type of lime applied affects the rate of movement; to evaluate the effect of surface application of lime on soil chemical properties; and to determine the correct application rate of lime for acidic NT soils. Three NT field sites were identified that had below‐optimal soil pH (<6.0) in the surface 15 cm. Various lime treatments were established in 2000 or 2002, consisting of differing rates [as kg effective calcium carbonate (ECC) ha−1] of either limestone (commercially available) or pelletized limestone, plus an unlimed control. In the spring of 2005, soil samples were taken to a depth of 30 cm; the surface 15 cm was separated into 2.5‐cm increments and the lower 15 cm was separated into 7.5‐cm increments. Evidence of lime movement was limited to 7.5 cm or less at all three NT sites, as indicated by significant increases in pH compared with the control. Type of liming material or frequency of limestone application seemed to have no effect on any variables measured. Significant yield increases were not observed for crops as a result of limestone applications. Limestone recommendations for NT production systems need to be based on correcting pH in the surface 7.5 cm for production systems receiving 800 to 1000 mm of annual precipitation.