Effects of Legume Green Manures on Forage Produced in Continuous Wheat Systems

Abstract

Inorganic N fertilizers are important to continuous systems of winter wheat (Triticum aestivum L. em Thell.) in the U.S. southern Great Plains (SGP). Costs have increased in recent years and resulted in producers considering summer‐grown legumes as green N sources. This study (2008–2012) defined effects of lablab [Lablab purpureus (L.) Sweet ‘Rio Verde’] cover crops on subsequent forage production by wheat under conventional and no‐till management, compared to soybean [Glycine max (L.) Merr. ‘Laredo’], two inorganic fertilizer rates (40; 80 kg N ha−1yr−1), and unfertilized controls. Inoculated legume seeds were sown annually after wheat harvest, grown during June to August, and terminated in early‐September. Wheat was sown late‐September and samples collected at four growth stages through maturity. Wheat forage (kg ha−1), N concentration (g kg−1) and N accumulated (kg N ha−1) in forage were analyzed to define treatment, tillage, growth stage, and year effects. Precipitation was 53 to 92% of long‐term average (LTA) for the wheat growing (October‐May) period (1977–2012; 688 mm). Treatment x year interaction was significant (P < 0.01) for biomass, N concentration, and N accumulated in forage. Treatment effects on forage production varied among years; response to legume treatments were ≤ control. Response of N concentration and N accumulated in forage under legume treatments were largely ≤ control; responses to all treatments declined with length of study. Neither legume was an effective N source for forage production by continuous wheat systems in the SGP.

Influence of Tillage Systems, and Forms and Rates of Nitrogen Fertilizers on CO2 and N2O Fluxes from Winter Wheat Cultivation in Oklahoma

“…Additionally, the flux rates from cowpea treatments were significantly lower than from the 45-N and 90-N treatments. These results corroborate the previous findings in the region, as poor growth and yield responses of winter wheat to legume-based green N are reported frequently [3,4,25,27,28]. Lack of interaction effects between the tillage systems and N treatments indicated that cowpea-based green manure could not replace inorganic N fertilizers in either tillage system.…”

“…A possible reason for similar canopy CO 2 fluxes from the contrasting tillage systems might be related to the lower intensity tillage applied under CT, which was restricted to the upper 20 cm of soil, and residues were left on the soil surface. Previous studies in the SGP have documented similar yield responses of winter wheat to NT and CT systems [3,22,23], and were corroborated by similar levels of GPP for tillage systems in this study. The short distance between sites, and difference in soil properties and fertility, allowed a test of effects of nitrogen and tillage treatments across a broad set of landscapes.…”

“…Regardless of crop usage, a 3-4 month period of summer fallow exists in continuous monocultures of winter wheat, to conserve limited and sporadic amounts of precipitation as soil moisture to support winter wheat [2]. However, legumes could be grown during the summer to serve as sources of green N for winter wheat [3]. The use of annual legumes as cover crops during summer represents one of a series of systems of intensified production [3][4][5] that may improve efficiencies in use of available soil water in the SGP [6], increase soil carbon (C), suppress weed populations, and reduce nutrient runoff or leaching [7].…”

Sewage Sludge Amendment Combined with Green Manuring to a Coastal Mudflat Salt-Soil in Eastern China: Effects on Soil Physicochemical Properties and Maize Yield

“…The past research mainly focused on the application of sewage sludge or green manuring in farmlands [31][32][33][34]. However, the application of sewage sludge combined with green manuring to amend mudflat salt-soils has received no attention.…”

Mothbean: A Potential Summer Crop for the Southern Great Plains

“…Past research has defined the potential use of some grain legumes as forage sources during summer [1] [6] [7] [8] [9] [10]. However, many of the tested legumes have significant amounts of large-diameter, low digestibility stems in their aboveground biomass which limits their applicability for grazing [8].…”