Influence of alternative and conventional agricultural management on soil microbial processes and nitrogen availability

Abstract

Microbial activities important to effects on crop productivity and nutrient cycling can be altered by agricultural management practices. This study was conducted to determine whether soil microbial populations and their N cycling activities differ between conventional and alternative management practices. Physical, chemical, and microbial soil properties were measured at soil depth intervals of 0 to 7.5, 7.5 to 15, and 15 to 30 cm at a site in southeastern Pennsylvania during the second and fifth years after conversion from a conventional, chemically intensive system to alternative systems utilizing legumes and animal manure as N sources. In the second year after conversion, populations of fungi and bacteria, dehydrogenase activity, and soil respiration in the surface soil layer were greatest with alternative systems planted to red clover (Trifolium pratense L.). Differences in soil biological factors between management systems were related primarily to crop characteristics and, to a lesser extent, to soil physical properties. Levels of microbial populations and activities with conventional management were the same as with alternative management systems when similar crops such as corn (Zea mays L.) or soybean [Glycine max (L.) Merrill] were grown. Soil NO3-N contents, at most sampling depths, were markedly increased by application of fertilizer N or recent plow-down of red clover or hairy vetch (Vicia villosa Roth). The growth of red clover in the second year or hairy vetch in the fifth year was accompanied by significantly increased microbial biomass and potentially mineralizable N (PMN) reserves in the top 30-cm soil layer-these changes being most pronounced in the surface 0- to 7.5-cm layer. Nitrogen deficiency symptoms and lower corn grain yields in a legume/cash grain rotation as compared with conventional management in the second year were associated with lower soil NO3, levels and a greater proportion of N present as weed biomass and belowground microbial biomass. In 1985, management systems comparisons were limited to corn as the main crop; soil NO3 levels during the growing season were inversely related to soil microbial biomass and PMN levels where hairy vetch was overseeded and incorporated as green manure by plowing before corn planting. Under the conditions of this study, the use of chemicals had little effect on microbial populations, their activity, or the cycling of nitrogen. Cropping systems-in particular, the growth of red clover or hairy vetch—profoundly influenced soil microbial biomass levels and soil pools of organic and available NO3-N during the growing season. Competitiveness of alternative management systems employing legumes as? sources for grain crops may depend largely on the grower's ability to synchronize supplies of available soil N with periods of maximum uptake by grain crops.

Challenging Balance between Productivity and Environmental Quality: Tillage Impacts

“…Stockfi sch et al (1999) concluded that "organic matt er stratifi cation and accumulation as result of long-term minimum tillage were completely lost by a single inversion tillage in the course of a relatively mild winter." Several experiments in North America have shown more SOC content in soils of conservation tillage compared to plow till seed beds (Doran, 1980(Doran, , 1987Doran et al, 1987;Rasmussen and Rohde, 1988;Tracy et al, 1990;Havlin et al, 1990;Kern and Johnson, 1993;Lafond et al, 1994;Reicosky, 2001a,b). Liebig et al (2005) reported "continuous cropping and no-tillage resulted in carbon accumulation of 0.27 Mg C/ha/yr, a value specifi c to the lower rainfall area of the U.S. Northern Plains.…”

Comparison of Organic and Integrated Nutrient Management Strategies for Reducing Soil N2O Emissions

“…Moreover, the ratio of N 2 O:N 2 produced via denitrification increases with increasing soil NO 3 concentrations [38], suggesting higher N 2 O emissions in soils with inorganic N application. By contrast, soils receiving primarily organic N sources tend to have lower levels of available NO 3 [47]. The majority of C and N added through organic amendments is stored in organic matter pools, which are less susceptible to N losses [48].…”

Effect of INM on Soil Carbon Pools, Soil Quality and Sustainability in Rice-Brown Sarson Cropping System of Kashmir Valley

“…Maintenance and management of soil fertility is the core for development of sustainable food production systems (Doran et al, 1988). The integrated plant nutrient supply system, by which we can apply the nutrients in balanced form, is emerging as the most logical concept for managing and sustaining long term soil fertility and productivity.…”