Evaluation of the Green Manure Potential of Austrian Winter Peas in Northern Idaho

The objective of this field study was to determine the effect of Austrian winter peas [Pisum sativum spp. arvense (L.) Poir] used as either a green manure (GMP) or seed pea (SP) crop on soil N levels, and yields of subsequent crops of winter wheat (Triticum aestivum L.) and spring barley (Hordeum vulgare L.). The Austrian winter pea-winter wheat-spring barley (GMP-WW-SB) rotation was compared with seed pea-winter wheat-spring barley (SP-WW-SB), spring barley-winter wheat-spring barley (SB-WW-SP), and summer fallow-winter wheat-spring barley (SF-WW-SB) cropping sequences at two sites similar in annual precipitation. After harvest of the initial rotational crop, plots were divided into four subplots and four rates of N were applied as a topdress application following planting of ‘Stephens’ winter wheat. Spring barley was planted the third year. Winter wheat yields, spring barley yields, and inorganic soil N were not significantly affected by rotation ✕ N fertilizer interactions. Winter wheat yield averages following GMP, SP, SF, and SB were 6.6, 6.4, 6.3, and 4.7 Mg ha⁻¹, respectively. Average N feitilizer equivalent values of 94, 75, and 68 kg ha⁻¹ were provided by GMP, SP, and SF, respectively, to the following winter wheat crop. Yield differences resulting from crop rotation or N fertilization rate were not observed in the third year of the cropping sequence. Austrian winter peas used as either a GMP or SP crop provided more inorganic N for the following winter wheat crop than SF or SB. From a 3-yr total yield the SP-WW-SB was the most efficient cropping sequence, as cereal yields were comparable to the GMP-WW-SB and SF-WW-SB rotations; however, since SP was harvested three crops instead of two (other rotations) were produced. Contribution from the College of Agric., Univ. of Idaho. Approved for publication by the Director of the Idaho Agric. Exp. Stn. as res. paper 88-7-25.