Effects of Tillage, Rotation, and Organic Inputs on Soil Ecological Properties in Vegetable Crop Production Systems
Agricultural management decisions that influence biological activity and diversity include tillage, fertilizer and pest-control inputs, and crop rotations. Our research objective was to characterize relationships between biological and physical properties resulting from long-term agricultural management decisions. A nine-year old factorially-designed field experiment was used to examine the effects of tillage (moldboard plow or strip-tillage), input (synthetic fertilizers and pesticides or inputs approved for organic certification programs), and crop rotation (continuous staked tomatoes or 3-year vegetable rotation) on a suite of biological and physical soil parameters. Biological measurements included microbial, nematode, and earthworm community composition, soil respiration and N mineralization potential, enzyme activity, and microbial biomass. Physical property measurements included aggregate stability, bulk density, and pore-size distribution. Biological properties generally responded to all treatment combinations, but tillage provided the strongest treatment effect in most cases. Compared to strip-tillage, moldboard tillage consistently yielded significantly lower values for the following biological measurements: total C and N, above-ground biomass, microbial biomass, enzyme activity, soil respiration, N mineralization, some nematode trophic groups, and earthworms. Compared with organic inputs, synthetic inputs consistently induced significantly lower values for the following biological measurements: microbial biomass, enzyme activity, some nematode trophic groups, and soil respiration. An examination of relationships between biological and physical parameters using redundancy analysis revealed that microporosity was the physical property that was most strongly correlated with most biological parameters. Soil organisms responded to treatments in the following order: tillage > input > rotation.
1. To evaluate the biological diversity of soils under different agricultural management strategies, recognizing that a highly productive agricultural soil is considered to be one with a high degree of biological activity and containing a stable cross section of microorganisms and invertebrates.
2. To make the best possible estimation of microbial and invertebrate populations and community structure using a range of direct enumeration and community evaluation techniques.
3. To assess the effect of microbial and invertebrate communities on the following soil physical properties: aggregate stability, bulk density, porosity, and pore size distribution.
4. To aid in the assessment of soil degradation by identifying soil biological indicators of high soil productivity potential for agricultural soils.
Soil biological measurements have been concluded for microbial, nematode, and earthworm community composition, soil respiration and N mineralization potential, enzyme activity, and microbial biomass. Physical property measurements that included aggregate stability, bulk density, and pore-size distribution are also finished. This experiment has completed the field and lab measurement phase and final conclusions are being written. Final publications of the work are in departmental or journal review.
Impacts and Contributions/Outcomes
We found that greatest biological activity among various field production systems was in those systems that had the least tillage. Changing production systems from chemical to organic also produced increased biological activity, but not to the the extent that tillage reduction did. We have given many workshops and speaker presentation on the findings of this research, with much interest from producers who want to achieve greater soil productity from their farm operation.
PhD Graduate Student
Dept. of Soil Science, NCSU
Raleigh, NC 27695-7619
Office Phone: 9195133037