Field trial assessment of biological, chemical, and physical responses of soil to tillage intensity, fertilization, and grazing.

Soil microbial populations can fluctuate in response to environmental changes and, therefore, are often used as biological indicators of soil quality. Soil chemical and physical parameters can also be used as indicators because they can vary in response to different management strategies. A long-term field trial was conducted to study the effects of different tillage systems (NT: no tillage, DH: disc harrow, and MP: moldboard plough), P fertilization (diammonium phosphate), and cattle grazing (in terms of crop residue consumption) in maize (Zea mays L.), sunflower (Heliantus annuus L.), and soybean (Glycine max L.) on soil biological, chemical, and physical parameters. The field trial was conducted for four crop years (2000/2001, 2001/2002, 2002/2003, and 2003/2004). Soil populations of Actinomycetes, Trichoderma spp., and Gliocladium spp. were 49% higher under conservation tillage systems, in soil amended with diammonium phosphate (DAP) and not previously grazed. Management practices also influenced soil chemical parameters, especially organic matter content and total N, which were 10% and 55% higher under NT than under MP. Aggregate stability was 61% higher in NT than in MP, 15% higher in P-fertilized soil, and also 9% higher in not grazed strips, bulk density being 12% lower in NT systems compared with MP. DAP application and the absence of grazing also reduced bulk density (3%). Using conservation tillage systems, fertilizing crops with DAP, and avoiding grazing contribute to soil health preservation and enhanced crop production.