Abstract
Background and aimsSoil nitrogen (N) immobilization from cover crop residues may help suppress weeds. We established a gradient of cereal rye shoot biomass to determine the extent that soil N can be immobilized and its effect on redroot pigweed (Amaranthus retroflexus L.).MethodsA microplot study was conducted in no-till cereal rye (Secale cereale L.)—soybean (Glycine max L. (Merr.)) systems at two sites in eastern USA. Microplots received 0, 2000, 5000, 8000, 12,000 or 15,000 kg ha−1 of cereal rye shoot biomass, and were injected with two mg 15N kg−1 soil 5 cm below the soil surface. Pigweeds were sown and allowed to germinate.ResultsMaximum rates of cereal rye shoot decomposition were observed at ≥5000 kg ha−1. Although cereal rye shoot N declined, shoots became enriched with 15N, indicating fungal transfer of soil N to shoots. Soil inorganic N declined by an average of 5 kg N ha−1. Pigweed tissue N and biomass were reduced in the presence of cereal rye. The magnitude of pigweed N reduction was similar across all shoot application rates.ConclusionsWe found weak evidence for a cereal rye shoot-based N immobilization mechanism of weed suppression. Our results indicate N immobilization may be primarily due to root residues.
Highlights
Demand for organic soybean (Glycine max L. (Merr.)) for both feedstock and human consumption has grown continuously over the past decade
Our results indicate N immobilization may be primarily due to root residues
Decomposition rates and estimated decay constants did not differ across the different shoot application rates
Summary
Demand for organic soybean (Glycine max L. (Merr.)) for both feedstock and human consumption has grown continuously over the past decade. Increased demand has driven commodity prices to near record highs, and in many cases organic soybean sells for twice that of conventional soybean (McBride et al 2015). Organic soybean production incurs considerably higher operational costs than conventional soybean production, arising primarily from higher fuel costs for weed management (McBride and Greene 2009). These higher operational costs have the potential to reduce the economic and environmental sustainability of organic soybean production systems, pointing to the need to develop alternative methods of organic weed control. Weeds in organic soybean systems are typically managed through frequent and intensive cultivation events. Williams School of Agriculture and Food Sciences, The University of Queensland, QLD, Gatton 4343, Australia
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