Abstract
Soil microbial biomass (SMB) is the main driving force in nutrient cycling and good indicator of soil productivity. A greenhouse experiment was designed to assess the effect of soil compaction, cropping system [sole maize, rotation 1 (inoculated soybean-maize), rotation 2 (un-inoculated soybean-maize) and intercrop 1(inoculated soybean-maize)and intercrop 2(un-inoculated soybean-maize)] and nitrogen fertilizeron soil microbial biomass C (SMB-C) and N (SMB-N) and their proportion to soil organic C and total N. SMB-C and SMB-N were higher in un-compacted than compacted soils with percent differences of 2.63 and 6.04% respectively. However, they were 19.32 and 36.36% lower in sole maize compared to rotation 1, 7.83 and 15.36% for rotation 2, 22.19 and 20.06% for intercrop 1 and 14.62 and 12.54% for intercrop 2. The results also showed that the application of 120 kg N ha-1 produced the highest soil microbial biomass as a percent of soil organic carbon, followed by 80 kg N ha-1, while the least value was obtained under zero application of nitrogen. Microbial biomass carbon and nitrogen as a percent of soil total nitrogen was significantly higher up to 80 kg N ha-1 before it decline at 120 kg N ha-1 suggesting better soil productivity improvement at 80 kg N ha-1 under the cropping systems with inoculated soybean. The findings indicate the need for inoculation in soybean-maize cropping systems to improve soil microbial biomass especially under less soil disturbances. Key words: Compaction, Brandyrhizobium Inoculation, Nitrogen fertilizer, microbial biomass, greenhouse.
Highlights
The predominant agricultural trends in the past 50 years have been intensive production with increased use of commercial seeds, fertilizers, pesticides, fuel (Tomich et al, 2011) and land use intensification
The results indicated that the initial values of microbial biomass carbon (MB-C), MB-N and Cmic/Nmic ratio obtained before setting up the greenhouse experiment were higher than those values obtained after the greenhouse experiment except that of MB-N in both soil compaction
The values of MB-N, MB-C and their percentage in soil organic carbon and total nitrogen were significantly lower in continuous sole maize than other cropping systems with soybean; significantly higher in inoculated soybeanmaize rotation
Summary
The predominant agricultural trends in the past 50 years have been intensive production with increased use of commercial seeds, fertilizers, pesticides, fuel (Tomich et al, 2011) and land use intensification. Consequences such as increased erosion, decreased soil fertility and biodiversity, water pollution and eutrophication, and alteration of atmospheric and climate processes lead to the urgency to develop new strategies that use the ecological interactions within the agricultural ecosystem (Matson et al, 1997). Soil respiration(CO2 production) is a useful indicator of soil organic matter (SOM) decomposition (Hassink, 1994; Lee et al, 1996) by both, aerobic and anaerobic microbes, which is a clear advantage over techniques based on O2 uptake (Sergio et al, 2011)
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