NCSOIL is a submodel of a larger program NTRM (nitrogen‐tillage‐residue management). NCSOIL computes short‐term dynamics of carbon and nitrogen organics, ammonium, and nitrate which result from the processes of residue decomposition, mineralization, immobilization, nitrification, and denitrification. Both total and isotopic nitrogen are considered. NCSOIL is built on the concept of catenary sequence of heterogenous substrates. The active soil organic phase is divided in two pools which are dynamic, defined by their kinetic rate constants and their position in the model structure. Residues are defined in terms of their chemical or morphological nature. A double feedback loop in the carbon flow adjusts the rate of residue decomposition and the efficiency factor to the availability of inorganic nitrogen. NCSOIL was calibrated with, and its behavior contrasted against published and unpublished data from an experiment reported by Chichester et al. in Soil Science (see p. 455, vol. 120): “Relative Mineralization Rates of Indigenous and Recently Incorporated 15‐N labeled Nitrogen.” Experimental results of the Chichester et al. experiment were discussed in view of computer‐simulated flow rates and substrate concentrations.

Agricultural source pollution of water resources has been a source of concern in recent years. Research is needed to define mechanisms of chemical and sediment loss in runoff from agricultural land, and to develop management practices that minimize transport of these pollutants. This study was designed to compare the effect of no‐till (NT) and conventional chisel‐till (CT) soil management on runoff water volumes, sediment loss, and N and P loss from small watersheds on a clay soil. Three NT and three CT watersheds located on Houston Black clay vertisol soil (fine, montmorillonitic, thermic, Udic Pellusterts) in east central Texas were used for the study. Wheat (Triticum aestivum L.), corn (Zea mays L.) and sorghum [Sorghum bicolor (L.) Moench] were grown rotationally on the watersheds from 1984 to 1989. Runoff amounts, sediment loss, and N and P losses were measured for each rainfall event that produced runoff. Runoff volume was not changed by tillage system and sediment loss and N and P losses in runoff were less, on average, from NT than from CT. Runoff averaged 1.3 ML ha−1 annually for both CT and NT. Average annual quantities for sediment and nutrient losses were: 160 kg ha−1 and 1575 kg ha−1 for sediment, 3.8 kg ha−1 and 8.1 kg ha−1 for N, and 0.8 kg ha−1 and 1.5 kg ha−1 for P for NT and CT, respectively. These results indicate that the loss of sediment and nutrients from agricultural lands could be minimized by using NT on clay soils.

Soil structural deterioration from wheel compaction can adversely affect crop development and root growth. This study was conducted to determine the effect of controlled-traffic lanes on soil physical properties and crop rooting for no-tillage and conventional tillage cropping systems on a swelling clay soil. Sorghum (Sorghum bicolor (L.) Moench), cotton (Gossypiu(!l hirsutum L.), and wheat (Triticum aesti11um L.) were field grown over 3 yr on an Austin silty-clay (finesilty, carbonatic, thermic Entic Haplustolls). Soil physical properties, including soil strength, bulk density, and total porosity, were not different between tillage treatments in the non-trafficked area during the crop growing season, but soil strength and bulk density were higher in the traffic lane of the no-tillage as compared to the conventional tillage treatments. Soil compaction in the traffic lanes was confined to the top 0.15-m soil layer and did not restrict root development in early stages of crop development. Root densities were lower in the top soil layer of the no-till traffic lane compared to the non-trafficked area at harvest, but were representative of values reported for these crops in the literature under conventional management practice. At depths > 0.3 m, root density was not affected by crop species, tillage, or traffic. Although controlled-traffic has been reported to improve soil physical properties and crop rooting, our data suggest it may not necessarily apply to all soils, especially soils with 40% or more 2:1 clay minerals. Soil moisture and nutrients under traffic lanes will be available to crops.Additional index words: Vertisol, Bulk density, Cone index, Total porosity, Soil water content, Root length density, Sorghum bicolor (L.) Moench, Gossypium hirsutum L., Triticum aesti11um L. 1 Contribution of the Texas Agric. Exp. Stn., Texas A&M Univ. Systems, in cooperation with USDA-ARS. Received 7 Apr. 1986. 2 Associate professor, Blackland Res. Ctr., PO Box 6112, Temple, TX 76503-6112, and agricultural engineer and soil scientist, USDA-ARS, PO Box 6112, Temple, TX 76503-6112. Published in Agron. J. 79:434-438 (1987).

No abstract

No abstract