Effect of Cultivation on Soil Organic Matter and Aggregate Stability

Agricultural sustainability relates directly to maintaining or enhancing soil quality. Soil quality studies in Canada during the 1980 s showed that loss of soil organic matter (SOM) and soil aggregate stability was standard features of non-sustainable land management in agroecosystems. In this study total soil organic carbon (SOC), particulate organic matter (POM), POM-C as a percentage of total SOC, and aggregate stability were determined for three cultivated fields and three adjacent grassland fields to a…

Some Eco-Physiological Characteristics at R4-R5 Stage in Relation to Soybean Yield Differing in Maturities

Digital plant canopy imager and photosynthesis analyzer system were used to analyze thecharacteristics of canopy structure, photosynthetic physiology and micro-environmentalfactors at R4-R5 stage in different yielding soybean cultivars or lines with differentmaturities. The results showed that the common characteristics of high yielding soybeancultivars were high LAI, uniform foliage distribution in all horizontal directions, lessvariance of photosynthetic rate between top and bottom leaves in canopy and relativelyhigher photosynthetic rate of the whole canopy. All these characters combined in allresulted in higher canopy photosynthetic productivity, and pod number, seed number andseed weight per plant, especially pod and seed number in top and middle canopy wereincreased. The characters of high yielding canopy varied among maturities. Light interceptionwas more important to early cultivars. Less foliage inclination angle was benefit tointercept more solar energy during yield formation. As late soybean cultivars had a moreclosure canopy and higher LAI, greater foliage inclination angle in all layers of highyielding canopy made more solar radiation penetrate into canopy, which was beneficial toyield formation.

Row Spacing in Relation to Competition for Limited Resources in Soybean (Glycine Max L. Merrill)

Growing soybeans in different row-spacings introduces competition. Competition begins when the immediate supply of a single necessary factor falls below the combined demands of all plants. This paper reviews the main competition factors of genotypes, light, water, nutrients and weed in responses to row spacings for the past four decades. It demonstrated that responses of soybean genotypes to row width differ among cultivars, which depend on seasonal rainfall and irrigation. Determinate types produce more yield in narrow-rows, and cultivars with lodging resistance should be adopted in narrow-spacings, but indeterminate soybean should also be used to optimize yields in certain system. Narrow-compared with wide-row soybean (Glycine max) cultivation increases light interception (LI) and dominant components for the increase come from LAI, light extinction coefficients and branch types. Water use efficiency (WUE) and evapotranspiration are not influenced by row spacing, but seed yield could be increased if irrigation is applied. Nutrient uptake is significantly affected by row spacing, seed yields and uptake of N, P, K in plants increases with decreasing row spacing, and the effects depend on the fertilizer levels. Other factors rather than row spacing affect nitrogen fixation. Weed density, peak time and periodicity of weed emergence are not affected by row spacing, but better complementary weed control by the herbicides at the used doses can be obtained in narrow spacing due to the reduced weed number and dry weight. More researches are required to investigate the physiological responses, nutrient and water uptake and translocation, light utilization at different layers of canopy and soil environment changes in different row-spacings.