Submitted to: Oklahoma Academy of Science Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/2002
Publication Date: 11/30/2002
Citation: GRESSETT, J.A., MACKOWN, C.T., NORTHUP, B.K., SLAGELL-GOSSEN, R. SPATIAL VARIABILITY AND RELATIONSHIPS AMONG SELECTED SOIL AND FORAGE TRAITS IN A WINTER WHEAT PASTURE. OKLAHOMA ACADEMY OF SCIENCE PROCEEDINGS. 2002. v. 82. p. 117. Interpretive Summary: Abstract only
Technical Abstract: Millions of stocker calves in the southern Great Plains are grazed each year on winter wheat (Triticum aestivum L.) pastures. During the first 3 weeks of grazing wheat, stockers often gain little or no weight even though the quality of forage is considered excellent. Because forage factors may affect stocker adaptation to wheat, spatial distributions of forage and soil traits in a 2-ha wheat pasture were measured to determine if soil traits could be used to predict forage availability and N composition. Samples were collected in a modified grid pattern with most samples spaced 5-m apart in eight rows spaced 15-m apart. Biomass ranged from 71 to 3980 kg/ha (mean = 1790 kg/ha, RSD = 35%) and had uniform protein level of 261 g/kg (RSD = 4%), but nitrate-N levels varied from 522 to 8420 mg/kg (mean = 4860 mg/kg, RSD = 31%). Nitrate-N levels exceeding 3.0 g/kg are potentially toxic to unadapted calves. Plant traits were unrelated to available soil N, which ranged from 16 to 249 kg/ha (mean = 72 kg/ha, RSD = 57%). Biomass was unrelated to soil pH (4.4 - 7.1), Mehlich III extractable P (22 to 135 mg/kg), and KCl extractable Al (1 to 32 mg/kg) in the top 10 cm of soil. Interpolated maps depicting distribution of traits across the wheat pasture demonstrate local scale variability and poor replication among map patterns. For pastures exhibiting forage with high nitrate, producers should evaluate variability in forage availability to insure stocking rates do not lead to excessive grazing and consumption of potentially high nitrate wheat stems.