Abstract:The Soil Conservation Service curve number (CN) method is widely used for predicting direct runoff from rainfall. However, despite the extent of cultivation on hillslope areas, very few attempts have been made to incorporate a slope factor into the CN method. The objectives of this study were (1) to evaluate existing approaches integrating slope in the CN method, and (2) to develop an equation incorporating a slope factor into the CN method for application in the steep slope areas of the Loess Plateau of China. The dataset consisted of 11 years of rainfall and runoff measurements from two experimental sites with slopes ranging from 14 to 140%. The results indicated that the standard CN method underestimated large runoff events and overestimated small events. For our experimental conditions, the optimized and non-optimized forms of the slope-modified CN method of the Erosion Productivity Impact Calculator model improved runoff prediction for steep slopes, but large runoff events were still underestimated and small ones overpredicted. Based on relationships between slope and the observed and theoretical CN values, an equation was developed that better predicted runoff depths with an R 2 of 0Ð822 and a linear regression slope of 0Ð807. This slope-adjusted CN equation appears to be the most appropriate for runoff prediction in the steep areas of the Loess Plateau of China.

No abstract

The nutrient availability of composts has to be known for their safe use in crop production. A field study was carried out to assess the effect of a spring application of composts and inorganic fertilizers on spring wheat (Triticum aestivum L. 'Messier') growth and N uptake in eastern Québec (Canada). The experiment was conducted in 1994 and 1995 on two different soils: a Kamouraska clay (Orthic Humic Gleysol) and a Saint-André sandy loam (Fragic Humo-Ferric Podzol). Four composts were applied at rates of 0, 90, 180 and 360 kg total N ha−1. Inorganic fertilizers were applied at rates of 0, 50, 100 and 200% of wheat N, P or K requirements. Treatments in which inorganic fertilizers (IN) were added to composts were also included. Grain yield was increased by N rates whereas composts alone at 90 kg total N ha–1 resulted in lower yields than the control in the first year on the sandy loam. Commercial composts resulted in higher yields than dairy manure composts. Wheat showed no significant response to P and K fertilizers on either soil. Compost rates had no effect on grain N content but commercial composts increased straw N by 36 to 63%. Addition of IN to composts increased grain yield by 0.1 to 1.5 Mg ha−1 and N uptake by 4 to 55 kg N ha−1, depending on soil and weather conditions. Apparent recovery efficiency of added N for composts was −14 to 15% whereas it ranged from 24 to 56% for IN. In spring wheat production, composts should be considered more as organic matter amendments because of their limited N efficiency. Key words: Composted dairy manure, shrimp wastes, peat moss, apparent N recovery

The addition of compost may mitigate soil degradation and contribute to the soil nutrient supply in spring cereal monoculture. A field study was carried out in eastern Quebec, Canada, to assess the impact of composts from four sources and ammonium nitrate (AN) applied at different rates in spring on soil moisture and inorganic N in spring wheat production (Triticum aestivum L. 'Messier'). The experiment was conducted in 1994 and 1995 on two different soils: a Kamouraska clay (Orthic Humic Gleysol) and a Saint-André sandy loam (Fragic Humo-Ferric Podzol). Composts were applied at rates of 0, 90, 180 and 360 kg total N ha−1. Ammonium nitrate was applied at 0, 45, 90 and 180 kg N ha–1. Treatments in which AN was added to composts were also included. Thirty days after N application, profile soil inorganic N increased linearly with rates of commercial composts and AN but not with farm composts, whereas at harvest, residual soil N was not affected by composts but was increased by AN. The relative contribution of the compost organic fraction was negligible in the first year of application. Soil inorganic N at 30 d after fertilizer applications was significantly related to plant N uptake at harvest (r2 = 0.74), suggesting useful index of compost N availability. Large amounts of compost raised soil moisture content of the sandy loam by 3–5%, particularly under dry climatic conditions. Commercial composts have a small N fertilizer value, whereas composted dairy manure should be considered preferable as a soil amendment. Key words: Dairy manure compost, shrimp wastes, peat moss, wheat

No abstract