Soil-Applied Nitrogen and Composted Manure Effects on Soybean Hay Quality and Grain Yield

Abstract

ABSTRACT Grain yield in many soybean experiments fails to respond to fertilizer nitrogen (N). A few positive responses have been reported when soybean were grown in the southern U.S., when N was applied near flowering and when biosolids were added. In a previous study, low N concentrations of soybean forage in north Texas on a high pH calcareous soil were reported and thus, we suspected a N nutrition problem. Consequently, we initiated this study to determine whether selected preplant N sources broadcast and incorporated into a Houston Black clay (fine, smectitic, thermic Udic Haplusterts) might increase forage N concentration, forage yield, or soybean grain yield. In 2003, N was applied as ammonium nitrate (NH4NO3, AN) up to 112 kg N ha− 1 and dairy manure compost (DMC) was applied at rates of 4.9, 9.9, 15.0, and 19.9 Mg ha− 1. The DMC contained 5.9, 2.6, and 6.7 g kg− 1 of total N, P, and K, respectively; thus DMC added 29 to 116 kg N ha− 1. In 2004, AN was applied at rates of 112 and 224 kg N ha− 1 and DMC was applied at 28 and 57 Mg ha− 1; thus, DMC added 168 to 335 kg N ha− 1. In another 2004 test, biosolids, a biosolids/municipal yard waste compost mixture (BYWC), and AN were compared. The biosolids contained 31, 18, and 2.9 g kg− 1 total N, P, and K, respectively. The BYWC mixture contained 8.8, 6.1, and 3.4 g kg− 1 of total N, P, and K, respectively. Biosolids were applied at 10 Mg ha− 1 (310 kg N ha− 1), BYWC was applied at 58 Mg ha− 1 (510 kg N ha− 1), and AN up to 224 kg N ha− 1. None of the soil treatments increased soybean grain yield or forage yield although AN slightly increased forage N concentration in 2003.