Soil quality indicators of a mature alley-cropping agroforestry system in temperate North America

Authors: UDAWATTA, RANJITH - University Of Missouri; Kremer, Robert; NELSON, KELLY - University Of Missouri; JOSE, SHIBU - University Of Missouri; BARDHAN, SOUGATA - University Of Missouri

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2014
Publication Date: N/A
Citation: N/A

Interpretive Summary: Alternative cropping practices, designed for profitable grain production and reduction of soil erosion and improvement of soil productivity, include agroforestry systems that incorporate production of grain crops. Agroforestry is a multiple-cropping land use system that involves simultaneous production of trees and agricultural crops. Both grain crops, planted in the alleys between tree rows, and trees diversify production systems through harvests of grain and tree crops that potentially increase farm profits. When tree rows are established in narrow strips with grass across landscape slopes, water runoff containing suspended soil and dissolved chemicals after rainfall is slowed compared with continuous row cropping on similar sloping land. Vegetative residues remaining in the alleys after crop harvest reduce surface soil erosion and build soil organic matter. Soil organic matter supports important biological processes such as making plant nutrients available and improving soil structure to allow water and air movement within the soil profile. Despite the known benefits in reducing soil loss, little information is available about how long-term agroforestry and alley-cropping practices affect soil biological properties and soil quality. Our objective was to compare differences in soil aggregation, soil carbon, soil nitrogen, and enzyme activities in cropping alleys and tree row strips in a mature alley-cropping practice in northeast Missouri. Silver maple trees were planted in 1990 in rows perpendicular to the slope at a row spacing of 19.2 meters (about 60 feet), which comprised the cropping alleys. A crop rotation of corn alternating annually with soybean followed by wheat in autumn was planted with no-till land preparation. Soil samples at three depths (0-4, 4-8, and 8-12 inch increments) were removed from crop alleys and tree rows and segregated by upper, middle, and lower landscape positions. All soil quality measurements were highest in the upper (0-4 inches) soil depth. Soil enzyme activities, soil quality measures that indicate extent of nutrient availability for plant growth, did not differ between tree row or cropping alley. Bulk density of soil was 13% higher in the cropping alley compared with tree row, likely due to crop production practices requiring heavy implement traffic across the cropped areas. Soil aggregate stability (indicator of soil structure), soil carbon and nitrogen contents did not differ between tree row and cropped alley regardless of landscape position or crop. With this long-term agroforestry practice, the biological measures did not differentiate management of soil under permanent tree-planted strips from that where crop rotation was practiced in the alleys. The 20-year old mature trees may contribute to overall soil quality by contributing vegetative biomass and organic matter from their extensive fibrous roots to alley crop organic matter and thereby improve soil quality within the alleys at a greater rate than with conventional cropping alone. Thus, results are important to farmers, conservationists, extension personnel, and other scientists because they illustrate the value of long-term agroforestry practices in improving soil quality throughout this alternative system. The measurements reported may be applied to similar systems, such as forage- and grazing-based alley management, for assessing soil conservation effects in established, mature agroforestry practices.

Technical Abstract: Although agroforestry practices are believed to improve soil quality, reports on long-term effects of alley cropping on soils within agroforestry in the temperate zone are limited. The objective of this study was to examine effects of management, landscape, and soil depth of an established agroforestry system on water-stable soil aggregates (WSA), soil carbon, soil nitrogen, and enzyme activity. Treatments were crop alley, tree buffer, soil depth, and landscape position. Silver maple (Acer saccharinum L.) rows within grass buffer strips were established in 1991 on a no-till corn (Zea mays L.)-soybean (Glycine max L.)-wheat (Triticum aestivum L.) rotation on a Mexico silt loam (fine, smectitic, mesic Vertic Epiaqualfs) in northeast Missouri. Soils from crop alleys and tree buffers were collected in three transects extending from upper to lower landscape positions at 0-10, 10-20, and 20-30 cm depths in 2011. Soil enzyme activities measured included: fluorescein diacetate hydrolase (FDA), Beta-glucosidase, glucosaminidase, and dehydrogenase. All measured parameters including enzyme activities and WSA decreased with soil depth for both treatments. At the 20-30 cm depth C, N, Beta-glucosidase activity, and WSA were similar for both buffer and crop alley. Bulk density and total nitrogen significantly differed (P<0.05) between the two management treatments at the 0-10 cm depth. Landscape position did not significantly influence management or soil depth effects. Results show that after 20 years, agroforestry buffers improved soil quality parameters in crop alleys as the entire system matured, with improvements extending throughout the soil profile.