Management of Soil Nutrients on Drylands in China for Sustainable Agriculture

Abstract

There are two constraints for crop production on drylands in China: a limited supply of water and a serious erosion potential, of which, the latter has resulted in soil degradation and low soil fertility. Due to erosion and limited nutrient inputs, crop production on drylands is not only limited by water stress, but also by nutrient stress. Low soil fertility has led to low yield and low water use efficiency. For maintenance of high soil fertility and high productivity, a rational nutrient input is the powerful and effective way. A benign nutrient input promotes plants' root growth and therefore extends water and nutrient uptake space; raises crop's capacities for absorbing and transferring water and nutrients from soiI, improves root activities, increases water transpiration and reduces water loss by evaporation, directly leading to the increase of photosynthesis. As a direct result, the crop yield and water use efficiency are increased. In addition, by benign nutrient input, the growth of bumper crops does not only provide a maximum of ground cover but supplies sufficient organic matter to aid in the maintenance of the all-important soil constituent. The increased permeability of soils to water under such conditions is certainly a factor of major importance. All this has a certain effect on reducing soil erosion.Cropping and rotation systems affect soil fertility and therefore soil nutrients. Using oil-bearing crops and forage grasses in rotation stabilizes the crop production that follows; interplanting or intercropping crops with green manure or legumes improves the soil fertility at the same time as crops are grown. Different cropping and rotation systems have been used on the drylands for improvement of soil nutrients and raising crop production. Organic fertilizer has long been adopted on the drylands for supply of various nutrients that plants need, playing a great role in maintenance of soil nutrient balance and crop production. Nitrogen deficiency occurs everywhere on the drylands and P in some places and on some lands, and thus supply of these two elements constitute the major component of the nutrient management. The application of N and P chemical fertilizers has made the crop production continuous increase, showing a great contribution to the sustainable agriculture. For increasing fertilizer efficiencies, organic fertiIizer has gone hand in hand with N fertilizer, but separated with P fertilizer, since the nutrients in the organic fertilizers are not present in the proportion required for plant uptake: N is usually too low, but P too high for plant requirement. Also, the N fertilizers have been applied with P fertilizers that often limit the N fertilizer efficiency. Deep application can place fertilizers in the layer where more water is available, nutrients are deficient, and more roots are present for efficiently using the nutrients from the fertilizers and the moisture from the soil. In addition, the deep application reduces N loss from the fertilizers by volatilization. Because of these advantages, the deep application is regarded as an effective way for increase of fertilizer efficiency as well as water use efficiency, having widely been used on the drylands. Early application can make the nutrients available to plants for a longer period, and can quickly activate the effectiveness of the fertilizers added to the soil when rainfall occurs after a long dry spell. The farmers have taken all the measures on the drylands for their crop production and sustainable agriculture.Management of soil nutrients becomes even more important in the future. For sustainable agriculture, more attention should be paid to the adequate supply of nutrients. This relates not only with economic returns, but also with environmental concerns. For achieving such an aim, development of methods that can predict or reflect the soiI nutrient-supplying capacities should be first considered. A benign approach to nutrient management is to reduce the need for fertiIizer. That would be done by more effective management of nutrient cycles, and full use of organic waste residues either from animals or crops, including their storage and application improvement as the nutrient sources should be considered as one of the major contents. Crop rotation or intercropping with legumes, planting legumes solely as green manure or forages should be further emphasized. The last, not the least, is the improvement of crop health as vigorously growing plants can better use nutrients, and can therefore transform more nutrients into economic products. Under such a condition, the limited water will be fully utilized and crop yields be certainly increased, and the ”circulus vitiosus” be totally changed, and the agriculture be sustained.