Maintenance and improvement of soil quality in continuous cropping systems is critical to sustaining agricultural productivity and environmental quality for future generations. This review focuses on lessons learned from long-term continuous cropping experiments. Soil organic carbon (SOC) is the most often reported attribute from long-term studies and is chosen as the most important indicator of soil quality and agronomic sustainability because of its impact on other physical, chemical and biological indicators of soil quality. Long-term studies have consistently shown the benefit of manures, adequate fertilization, and crop rotation on maintaining agronomic productivity by increasing C inputs into the soil. However, even with crop rotation and manure additions, continuous cropping results in a decline in SOC, although the rate and magnitude of the decline is affected by cropping and tillage system, climate and soil. In the oldest of these studies, the influence of tillage on SOC and dependent soil quality indicators can only be inferred from rotation treatments which included ley rotations (with their reduced frequency of tillage). The impact of tillage per se on SOC and soil quality has only been tested in the ‘long-term’ for about 30 yrs, since the advent of conservation tillage techniques, and only in developed countries in temperate regions. Long-term conservation tillage studies have shown that, within climatic limits: Conservation tillage can sustain or actually increase SOC when coupled with intensive cropping systems; and the need for sound rotation practices in order to maintain agronomic productivity and economic sustainability is more critical in conservation tillage systems than conventional tillage systems. Long-term tillage studies are in their infancy. Preserving and improving these valuable resources is critical to our development of soil management practices for sustaining soil quality in continuous cropping systems.

The role of soil organic matter in maintaining soil quality in continuous cropping systems

Agricultural intensification, soil biodiversity and agroecosystem function

We examined the importance of terrestrial detrital inputs to secondary productivity of a headwater stream. Following a year of pretreatment studies on two headwater streams, we excluded terrestrial litter inputs (=treatment) to one stream while using the other as a reference. We excluded litter for 3 yr followed by 1 yr of small woody debris (≤10 cm diameter) removal and litter exclusion. Monthly benthic samples were collected from dominant mixed substrate (cobble, pebble, and sand-silt) as well as from moss-covered bedrock outcrop substrates. We used randomized intervention analysis (RIA) to test the null hypotheses that no change in abundance or biomass of functional feeding groups or specific taxa occurred in the treatment stream relative to the reference stream. Benthic organic matter was significantly lower in mixed substrate habitats of the treatment stream; however, small woody debris did not show a significant reduction prior to manual removal during year 4. At the end of the treatment period, tot...

https://www.jstor.org/stable/pdfplus/2657224.pdf

Effects of resource limitation on a detrital‐based ecosystem

The observed and projected increase in emission of greenhouse gases, with attendant effects on global warming and sea level rise, have raised interests in identifying mitigation options. Terrestrial C sequestration involves capture of atmospheric C through photosynthesis and storage in biota, soil and wetlands. Land use, vegetation and soil management have a strong impact on the biotic processes of C sequestration. Losses of C from the terrestrial ecosystems are exacerbated by deforestation, biomass burning, plowing, resource-based and subsistence agriculture, and practices that mine soil fertility and deplete the soil organic C (SOC) pool. Biomass burning may also produce charcoal, which is an inert carbon with long residence time. Practices that enhance C sequestration include afforestation and reforestation, conservation tillage and mulch farming, integrated nutrient management and adopting systems with high biodiversity. Net C sequestration within an ecosystem can be assessed by taking into account the hidden C costs of fertilizers, pesticides, tillage, irrigation and other input. Restoration of degraded soils and ecosystems has a vast potential of C sequestration. The Kyoto Protocol provides for C sequestration in terrestrial sinks and C trading through Clean Development Mechanisms. Terrestrial C sequestration, besides being a win–win strategy, offers a window of opportunity for the first few decades of the 21st century. It is a natural process of reducing the rates of gaseous emissions while alternatives to fossil fuel take effect.

/pdf/agricultural-activities-and-the-global-carbon-cycle-su6moqia85.pdf

Agricultural activities and the global carbon cycle

Factors Affecting the Abundance of Earthworms in Soils

Abundance and distribution of earthworms were studied on the Georgia Piedmont of the Southeastern U.S.A., at sites representing various ecosystem types, management practices, landscape positions, soil textures and soil erosion status. Earthworm abundance showed distinct seasonal patterns, with winter/spring maxima and summer minima. Numbers and biomass ranged from zero in plowed. mono-cropped soil at an upland site to over 1000 m-2 ( > 25g ash-free dry wt m-2) in no-tillage, double-cropped soil on bottomlands. Numbers and biomass in plowed, double-cropped soil, in a bottomland forest, and in grass meadows at both upland and bottomland sites were intermediate. Soil texture, as influenced by water erosion, strongly affected earthworm abundance. Moderately and severely eroded sandy clay loam supported significantly higher earthworm numbers and biomass than did slightly eroded soil with higher sand content. This effect may have resulted from low organic content and water holding capacity of the sandy soils. Of the soil texture variables, silt content was most highly correlated with earthworm biomass. Earthworm abundance was also related to quantity and quality of plant residue inputs in the agroecosystems, and to standing stocks of soil organic carbon across all sites studied. At most agroecosystem and forest sites, the predominant earthworm species were European lumbricids; native Diplocardia spp were most prominent in a meadow soil with high organic content.

R.R. Bruce

Papers

Abundance and distribution of earthworms in relation to landscape factors on the Georgia Piedmont, U.S.A.