Improvement of the soil fertility of a volcanic indurate layer (Tepetate) by applying acid treated biosolids
Volcanic indurate matter produces low soil fertility when rises to the surface, reducing the agricultural potential of the land and distressing marginal zones that live from agriculture. The habilitation of these materials using biosolids has not been explored, although the problem exists in several countries around the world. This work evaluated the impact of the application of biosolids on the fertility of a fragmented volcanic indurate layer (Tepetate). Tepetate’s fertility was measured before and after biosolids application with three biosolids application rates: agronomic rate (AR), as well as 10 and 20xAR. Biosolids were mixed with Tepetate and kept in pots under green house conditions along with a control, during four months. One set of pots with and without vegetative species. Organic matter content increased between 180 and 470% compared to the control. Cation exchange capacity (21.8 to 42.3 Cmol+kg-) resulted adequate for keeping nutrients for plants. pH values were adequate for agricultural activities (5.9-7.2). Dry color of the Tepetate, becomes darker (grayish brown; 10YR 5/2) than the initial yellowish brown (10YR 5/4) because of the addition of stable organic matter from biosolids. Considering edaphologic characteristics it is suitable to habilitate volcanic indurate layer by the application of biosolids.
The role of biology in the formation, stabilization and degradation of soil structure
Abstract Soil structure is defined as the arrangement of particles and associated pores in soils across the size range from nanometres to centimetres. Biologic influences can be demonstrated in the formation and stabilization of aggregates but it is necessary to distinguish clearly between those forces or agencies which create aggregations of particles and those which stabilize or degrade such aggregations. The formation of soil structure involves the physical forces of shrinking and swelling created by changes in water status of soils, freezing and thawing, tillage, or by movement of the larger biota in soils. Expansive properties of soils are controlled by the clay content. Thus changes of structural organisation are minimal in sands and maximal in clays. Plant roots, earthworms and other macrofauna large enough to move soil particles create pores recognisable by cylindrical shapes and smooth curved surfaces. Various visual and microscopic techniques aided by dyes are available to demonstrate the extent of biovoids in soils. Biology plays a major role in stabilization of soil structure. The major factors vary depending on the scale of soil structure. At larger scales plant roots and associated hyphae can be seen to enmesh soil particles by acting as a “sticky string bag”. At the microscale the influence of mucilages from roots, hyphae, bacteria and fauna such as earthworms can be shown by a range of microscopic techniques to be involved in stabilizing smaller aggregates and the linings of biopores. Techniques include optical and fluorescence microscopy, scanning electron microscopy including EDAX, transmission electron microscopy using heavy metals or other electron dense staining techniques for specific chemical compounds, and computer aided tomography. The microscopic techniques can be used on individual aggregates, stabilized soils, sections or separates of soils. Both microflora and fauna are involved in the degradation of stabilizing agents. Fauna may comminute roots and hyphae which stabilized larger aggregates and microorganisms utilize mucilaginous stabilizing agents as an energy source resulting in a slow breakdown of structural stability. Such effects can be established by combinations of studies of aggregation including microscopy. Further destruction of structure is caused by tillage and compaction by vehicles and animals.
Effect of Soybean Cyst Nematode (Heterodera glycines) on Yield of Resistant and Susceptible Soybean Cultivars Grown in Ohio.
Soybean (Glycine max) producers in Ohio rarely use soybean cyst nematode (Heterodera glycines, SCN)-resistant cultivars because of concerns over limited yield potential and lack of resistance to Phytophthora sojae. A two-year study was initiated to determine grain yield and nematode population increase on soybean cyst nematode-resistant cultivars in maturity groups II and III in production fields. Sites differed in soil texture, nematode densities, and P. sojae infestation at a number of locations in Ohio. Soil was assayed for nematode densities before planting and at harvest. Yields of resistant cultivars averaged 0% to 18% higher than those of susceptible cultivars in fine-textured soils with average preplant populations ranging from 463 to 14,330 SCN eggs/100 cm(3) soil. In coarse-textured soils, yields of susceptible cultivars were 21% to 56% less than the resistant cultivars with average preplant densities ranging from 1,661 to 15,558 SCN eggs/100 cm(3) soil. The reproductive index ranged from 0.1 to 5.5 for resistant cultivars and 0.4 to 112 for susceptible cultivars. In 1993, yield of P. sojae-susceptible, nematode-resistant 'Asgrow A 3431' was as high as yield of the P. sojae-resistant, nematode-susceptible cultivar 'Resnik' in a Phytophthora-infested field. The nematode-resistant cultivars Madison Experimental 131527 and Asgrow A3431 had higher yields than AgVenture AV1341 and susceptible cultivars Resnik and Kenwood when compared over five nematode-infested sites. Nematode-resistant cultivars were found to be excellent alternatives to currently grown susceptible cultivars for managing SCN where group III cultivars are used. However, better cultivar alternatives may be needed for sites with combined Phytophthora root rot and cyst nematode problems.