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Accueil du site → Doctorat → Chine → 2008 → Utilization of Residual N by Crops and Organic N in Surface-Mulched Soil on Dryland of North-Western China

Northwest University of Science and Technology (2008)

Utilization of Residual N by Crops and Organic N in Surface-Mulched Soil on Dryland of North-Western China

Wang Xi Na

Titre : Utilization of Residual N by Crops and Organic N in Surface-Mulched Soil on Dryland of North-Western China

Auteur : Wang Xi Na

Grade : Doctoral Dissertation 2008

Université : Northwest University of Science and Technology

Résumé partiel
On dryland of north-western China, where a little rainfall was received with high variability over seasons, apart from utilization by crops, a great deal of fertilizer N applied is found remained in the soil. The residual N has proved to be a threat to environment because it can be lost to atmosphere by the gas of NH3、N2O and so on, or be leached to deep soil and then enter into groundwater. However, as an essential nutrient to crops, residual N was benefit for maintaining soil productivity by compensating soil N pool. Therefore, it is of great importance to study how to prevent residual N loss from soil and how to make it be fully and efficiently used by crops.Straw mulching and plastic-film mulching over the soil surface were two agricultural measures to improve crop yield in arid and semi-arid region. Studying the effects of straw mulching and plastic-film mulching cultivation on soil fertility concerned the sustainability of dry land agriculture. Soil organic matter (SOM) contents were the important index for soil fertility. Light fraction organic matter (LFOM) is one of the labile forms of organic matter in soil, which consists of partially decomposed plant tissue, the hyphea and spores of fungi, seed, the debris of animals and microorganisms, and mineral granules. This pool turns over rapidly due to high C and N content, and serves as a readily decomposable substrate for soil microorganisms and a short-term reservoir of plant nutrients. Also, it is an important indicator of early changes in soil organic matter resulted from soil management. The N in soil LFOM is called light fraction organic N (LFN), which is closely relative to soil N mineralization and is a natural indicator for soil N fertility.Two long-term field experiments were conducted in southern region of Loess Plateau, in which different N rates and planting manners were setup and winter wheat and summer maize were planted. One experiment was to study the action of soil residual N and its utilization by following crops. The other was to study the change of soil organic C and N, light fraction organic C and N, and mineral N in soil on the conditions of straw mulching and plastic-film mulching on soil surface, by compared to conventional cultivation (no mulch). Transform of fertilizer N and straw N to soil organic N and LFN was also investigated by 15N-labeled method. The objective is to provide theory support for optimizing crop cultivation and nutrient management, improving soil fertility, and elevating crop production with high yield and high efficiency.1. Residual mineral N in dryland soil was found increased with the increase of N rates, in which the majority was nitrate N. In the first rotation of winter wheat and summer maize, the amount of residual mineral N in 0-300cm soil profiles could be as high as 449 kg hm-2, of which nitrate N accounted for 93.2%. During the following years of cropping, a part of nitrate N was gradually leached to layers below 300cm by rainfall. The amount of residual ammonium N was greatly affected by rainfall and soil moisture. In the warm summer with plenty of rainfall, the amount of ammonium N was low because the soil moisture was benefit for the nitrification of ammonium N. while the amount is high in dry seasons.2. Soil residual N could improve crop growth and N, P, K nutrients uptake, in which the effects on biomass and N uptake for the following winter wheat and summer maize were more significance. The effects of residual mineral N due to N fertilization could at least last to the fourth rotation of winter wheat and summer maize. Whereas, the residual effect of N fertilization was lied on crop species, climate, rainfall, temperature and so on, and showed variance among seasons and years.3. Measurement of the 15N- labeled fertilizer showed that the total fertilizer N use efficiency was only about 50% over four consecutive year rotation of winter wheat and summer maize. In the first year of rotation, fertilizer N use efficiency by winter wheat and summer maize was 32.3% and 9.3%, respectively, and only about 10% in last 3 years. Fertilizer N recovered by soil was 15.0-19.0 % and the lost accounted for 29.7-38.1% for 4 years. And that, a majority of residual fertilizer N were lost in the first summer maize season.4. During winter wheat growing season, straw mulch on soil surface is benefit for the accumulation of organic N, while plastic-film mulching makes soil organic C and N tend to decompose. In straw mulching cultivation, soil organic N in 0-40 cm soil layer was increased at the wheat dormant stage, and then gradually decreased at turning green stage. In which the amount of organic N was higher than that in conventional cultivation, and the difference was increased from 36 kg hm-2 at seeding to 153 kg hm-2 at harvest.

Mots clés : dry land soil residual nitrogen (N) organic N light fraction organic nitrogen (LFN)

Présentation (Dissertationtopic)

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