Soil Microbial Biomass and Its Relationship with Yields of Irrigated Wheat under Long-term Conservation Management
Lupwayi, N.Z., Larney, F.J., Blackshaw, R.E., Pearson, D.C., Eastman, A.H. (2018). Soil Microbial Biomass and Its Relationship with Yields of Irrigated Wheat under Long-term Conservation Management. Soil Science, [online] 183(5), 179-187. http://dx.doi.org/10.1097/SS.0000000000000242
Plain language summary
To appreciate the value of soil microorganisms, it is important to relate their mass and activities to crop productivity. Over a 10-year period, we evaluated the effects of conservation management practices on soil microbial biomass, and related the soil microbial biomass to wheat yields. These conservation practices included addition of composted cattle manure, reduced tillage, diverse crop rotations that had wheat, potato, dry bean and sugar beet, and use of cover crops. When crop rotations of the same length were compared, conservation management increased soil microbial biomass by up to 36%. Soil microbial biomass was associated with increasing wheat yields up to a certain point before declining. These effects were related to the compost and crop carbon inputs to the soil, which impacted soil organic matter contents. Therefore, conservation management resulted in a cycle of high microbial biomass and high wheat yields.
Relating soil microbial properties to crop productivity is important to appreciate the value of soil microbial activities in sustainable agriculture. Over a 10-year period, we evaluated the effects of conservation (CONS) management practices on soil microbial biomass carbon (MBC). The CONS practices included addition of composted cattle manure; reduced tillage; diverse crop rotations that comprised wheat (Triticum aestivum L.), potato (Solanum tuberosum L.), dry bean (Phaseolus vulgaris L.), and sugar beet (Beta vulgaris L.); and use of cover crops. The CONS management was applied to 3- to 5-year irrigated crop rotations and compared with conventional (CONV) management systems that did not have any of the CONS practices. Continuous wheat was also included. We then related MBC to wheat yields. Averaged over the 10-year period, CONS management overall increased MBC in wheat rhizosphere and bulk soil by 18% and 34%, respectively. When rotations of the same length were compared, CONS management in 3-year rotations increased rhizosphere MBC by 18% and bulk soil MBC by 30%; the corresponding increases in 4-year rotations were 13% and 36%. Regressions between soil MBC and wheat yields were quadratic, with MBC in wheat rhizosphere associated with increasing wheat yields up to 720 mg C kg soil. The corresponding value for MBC in bulk soil was 645 mg C kg soil. These effects were related to the compost and crop C inputs to the soil, which impacted soil organic C contents. Therefore, CONS management resulted in a cycle of high MBC and high wheat yields.