Effects of contour hedgerows on water and soil conservation,crop productivity and nutrient budget for slope farmland in the Three Gorges Region (TGR) of China

Soil erosion has long been recognized as a major environmental problem in the Three Gorges Region (TGR) where slope farming is commonly practiced but the local topography is hilly. In consideration of the poor socioeconomic position of local farmers, low cost hedgerows had been introduced as a soil conservation measure to the TGR in the late 1980s. A collaborative research programme was initiated by the Chinese University of Hong Kong, the Chinese Academy of Science, the Huazhong Agricultural University, and the Bureau of Soil and Water Conservation of Zigui County to study the potential of adopting hedgerows in the TGR. Six experimental plots (10 m × 2 m, gradient = 25°) were constructed at Zigui County, Hubei Province to study effects of hedgerows on erosion, nutrient loss and crop productivity. Results indicated that there were significant relationships between rainfall and runoff, and rainfall and soil loss, respectively. Conventional slope farming could not be considered a sustainable agricultural practice because it resulted in severe erosion and low crop yield. Hedgerows per se seemed not to be effective in reducing soil loss and boosting crop productivity, but performances could be greatly improved when they combined with the use of fertilizers. Current farming and fertilization practices, however, generally did not meet N demands of crops. Results and findings of this paper will contribute towards a technical reference for the promotion and adoption of hedgerows in the TGR.     

Photosynthesis,growth and yield of soybean and maize in a tree-based agroforestry intercropping system on the Loess Plateau

Agroforestry is the most effective way to restore the disturbed lands on the Loess Plateau and to develop the poor local economy. In order to maximize the potential benefits of tree-based intercropping systems, photosynthesis, growth and yield of soybean and corn were studied by measuring photosynthetic active radiation (PAR), plant water deficit and soil moisture in a 4-year-old plantation of walnut (Juglans regia L.) and plum (Prunus salicina) grown at a spacing of 5 m × 3 m on the Loess Plateau. The effects of tree competition significantly reduced PAR, net assimilation (NA), growth and yield of individual soybean or corn plants growing nearer (1 m near tree row) to tree rows. NA was highly correlated with growth and yield of the both crops. These correlations were higher for corn than soybeans, with corn, rather than soybeans being more adversely impacted by tree shading. Plum, rather than walnut had the greatest competitive effect on PAR and NA. Daily plant water deficits were non-significantly and poorly correlated with NA and growth and yield of the both crops. However, soil moisture (20 cm depth) was significantly correlated with biomass and yield of both crops. Possible remediation strategies are discussed to reduce tree competitive interactions on agricultural crops.     

Effects of organic and mineral fertilizer inputs on maize yield and soil chemical properties in a maize cropping system in Meru South District, Kenya

Soil nutrient depletion as a result of continuous cultivation of soils without adequate addition of external inputs is a major challenge in the highlands of Kenya. An experiment was set up in Meru South District, Kenya in 2000 to investigate the effects of different soil-incorporated organic (manure, Tithonia diversifolia, Calliandra calothyrsus, Leucaena leucocephala) and mineral fertilizer inputs on maize yield, and soil chemical properties over seven seasons. On average, tithonia treatments (with or without half recommended rate of mineral fertilizer) gave the highest grain yield (5.5 and 5.4 Mg ha⁻¹ respectively) while the control treatment gave the lowest yield (1.5 Mg ha⁻¹). After 2 years of trial implementation, total soil carbon and nitrogen contents were improved with the application of organic residues, and manure in particular improved soil calcium content. Results of the economic analysis indicated that on average across the seven seasons, tithonia with half recommended rate of mineral fertilizer treatment recorded the highest net benefit (USD 787 ha⁻¹) while the control recorded the lowest (USD 272 ha⁻¹). However, returns to labor or benefit-cost ratios were in most cases not significantly improved when organic materials were used.     

Influence of three plant species with different morphologies on water runoff and soil loss in a dry-warm river valley, SW China

Understanding of the effects of isolated plants with different morphologies on water runoff and soil loss is important for vegetation restoration in arid environments. We selected three representative species (Artemisia gmelinii; Ajania potaninii; Pulicaria chrysantha) of the dry-warm river valley of the upper reach of Minjiang River, SW China to examine these effects. Twenty-five runoff events were recorded using runoff plots at micro scale (<40 cm × 40 cm) on a south facing slope from July through October 2006. A. potaninii had sparse canopy, the smallest leaf area (0.49 ± 0.25 cm²) and specific leaf area (67.8 ± 16.5 cm²/g), and the highest leaf relative water content (27.1 ± 4.4%). It is the most resistant to drought stress. A. gmelinii was the shortest, and had relatively small leaf area (0.55 ± 0.50 cm²) and the densest canopy. P. chrysantha had the greatest leaf area (1.41 ± 0.49 cm²) and most extended canopy (4450 ± 1646 cm²). Dead branches and leaves of A. gmelinii and P. chrysantha commonly fall and collect on the soil surface. Thus they had greater improvements on soil porosity and soil water content, and higher effectiveness in controlling soil loss. However, A. gmelinii had more stable effectiveness in controlling runoff as compared with P. chrysantha. The characteristics such as relatively small leaf area but low height and dense canopy might be one criterion for selecting species to improve soil properties and controlling runoff and soil loss. Differences in soil environments, and runoff and soil loss production capacity for micro-surfaces regulates water and materials redistribution, which emphasizes the importance in designing vegetation restoration pattern.