| Wheat (Triticum aestivumLinn.) and rice(Oryza.sativa L.) are human’s main food crop. It is especially important for human’s nutritional status to improve their zinc content. This paper studied the effects of nitrogen fertilization and application methods on zinc availability in wheat and rice system. The main conclusions were as follows:(1) Zinc nutrition had a very important role for improving wheat grain yield. High N and high Zn significantly increased the wheat grain capacity. High nitrogen supply was an important factor for improving the wheat grain zinc content. Combination use of N and Zn fertilizers markedly increased wheat grain zinc content. Increasing N application under low Zn fertilizer, the grain zinc mainly came from the root zinc uptake. While increasing N application under high Zn fertilizer, the grain zinc mainly came from the straw zinc remobilization.(2) Application of nitrate fertilizer could significantly promote the grain biomass and the zinc content of the roots. Application of ammonium nitrogen could significantly increase the zinc contents of the shoots and grains. Application of DCD was more conducive to the accumulation of Zn in the shoots. Sole application of ammonium nitrogen or nitrate nitrogen could both increase the zinc content in rhizosphere soil. Application of urea could promote the root absorption of zinc, so that decreased the available zinc content in rhizosphere soil.(3)The available zinc content in crop soil was higher than that of no crops in root zone. In wheat season, the increased zinc was mainly the exchangeable zinc content, while, in the rice season, the increased zinc was mainly the exchangeable and loosely combined organic zinc content. The zinc form in the soil constantly changed and various forms mutual transformed. When soil transited from the dry land into paddy, soil Ex-zinc content and Min-zinc content increase, Wbo-zinc changed less, Carb-zinc content, OxMn-zinc content and Sbo-zinc content significantly reduced. That was to say that soil Wbo-zinc and OxMn-zinc could translate to exchangeable, and with the distance from the root zone closer the transformation was obvious.The Ex-zinc and the wbo-zinc content in the soil could directly affect the amount of zinc uptake by rice, which two forms of zinc were available zinc for rice. For wheat, the wheat Zn concentration and Zn uptake were only positive correlated with the root zone of available zinc and exchangeable zinc, but not the other forms and other areas zinc content.(4) Wheat season application zinc could significantly improve next stubble crops rice biomass of shoot, but not significant for rice zinc content of shoot. The zinc utilization rate was different in different application zinc period. Application zinc in rice season the zinc utilization rate was highest in four application fertilization treatments. Both application zinc in wheat and rice could significantly improve the plant biomass and zinc absorption, but decrease the zinc utilization.The exchangeable zinc content in the soil was increased and the loose bound organsed zinc content decreased when the soil turn to paddy, and the carbonate bound zinc, manganese oxide bound zinc, organically bound zinc significant decreased, the mineral zinc content increased.In the wheat-rice rotation condition, appilcate zinc in the rice season could significantly increase the content of exchangeable and loose bound to organic zinc in the soil and increase the absorption of exchangeable zinc by rice. Applicate zinc in wheat season, during the wheat growth, its effect was very small on exchangeable and loose bound to organic zinc in the blank soil, but could promote carbonate bound zinc of the root zone soil transformate to exchangeable and loose bound to organic zinc when growing plants. When the soil turned to the flooding situation, which could promote the exchangeable zinc to transform and increase the utilization of exchangeable Zn by rice. Whether applicate zinc in rice season had no influence on carbonate and manganese oxide bound zinc. |
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