Grain Legumes in Northern Great Plains: Impacts on Selected Biological Soil Processes

Abstract

Cropping systems in the Northern Great Plains have shifted from fallow‐based to legume‐based systems. The introduction of grain legumes has impacted soil organisms, including both symbiotic and nonsymbiotic N‐fixing bacteria, pathogens, mycorrhizae and fauna, and the processes they perform. These changes occur through effects of legume seed exudates, rhizosphere exudates, and decomposing crop residues. The legume–Rhizobium symbiosis results in dinitrogen (N2) fixation that adds plant available N into the soil system. It is estimated that about 171 million kg N2 was fixed by field pea (Pisum sativum L.), lentil (Lens culinaris Medik.), dry bean (Phaseolus vulgaris L.), and chickpea (Cicer arietinum L.) crops in the Canadian Prairies in 2004, representing 7% of the total fertilizer‐N (2580 million kg) used by Canadian prairie farmers in that year. Similarly, an estimated 40 million kg N2 was fixed by field pea, lentil, and dry bean (including chickpea) crops in U.S. agroecosystems in 2004. Some of the fixed N2 is recycled for the benefit of nonlegume crops grown after grain legumes. Many other associations benefit from the legume in a cropping system, including mycorrhizal associations that improve plant nutrient and water uptake, changes in the pathogen load and disease development, and overall changes in the soil community. Legumes contribute to greenhouse gas (N2O and CO2) emissions during nitrification and denitrification of fixed N. However, because less fertilizer‐N is used in legume‐based cropping systems, overall greenhouse gas emissions are usually less than those in fertilized monoculture cereals. Therefore, grain legumes in Northern Great Plains have positive effects on agriculture by adding and recycling biologically fixed N2, enhancing nutrient uptake, reducing greenhouse gas emissions by reducing N fertilizer use, and breaking nonlegume crop pest cycles.

Recycling of legume residues for nitrogen economy and higher productivity in maize (Zea mays)–wheat (Triticum aestivum) cropping system

“…legumes) was higher than sole maize. Intercropped legumes might have benefited the associated maize not only due to transfer of biologically fixed N 2 released in root exudates (Singh 1983;Subba Rao et al 2001) but also by sparing effect of N (Lupwayi and Kennedy 2007). Accordingly, cereal-legume association proved to be more effective in increasing productivity and N utilization, leading to its higher uptake.…”

“…Intercropped legumes benefit the associated cereal crop like maize by either transferring a part of fixed N 2 or sparing effect because of their less N requirement (Singh 1983;Subba Rao et al 2001;Lupwayi and Kennedy 2007). These also provide a good canopy cover in the early stages to control soil loss through erosion especially on slopped lands and also to control weeds (Khola et al 1999).…”

Energy budgeting and carbon footprint of transgenic cotton–wheat production system through peanut intercropping and FYM addition

“…Transgenic cotton hybrids are sown at wider row spacing (90-120 cm) and hence providing sufficient space for cultivation of short duration intercrop like peanut (Waterworth 1994;Singh et al 2009). Intercropped peanut benefits the associated cotton crop either by transferring a part of fixed N 2 or by sparing effect because of their less N requirement (Subba Rao et al 2001;Lupwayi and Kennedy 2007).…”

Beneficial management practices and mitigation of greenhouse gas emissions in the agriculture of the Canadian Prairie: a review

“…The authors expected less emission in western compared to eastern Canada (Helgason et al 2005). In general, because less fertilizer is used in legume based cropping systems, the overall GHG emissions are usually less than those in fertilized monocots (Lupwayi and Kennedy 2007).…”