【作者】 王西娜；

【导师】 王朝辉；

【作者基本信息】 西北农林科技大学 ， 植物营养学， 2005， 硕士

【摘要】 施用氮肥是主要的农业增产措施,适量氮肥对提高作物产量和维持土地生产力具有重要的意义。然而,长期不合理的氮肥投入导致大量矿质态氮残留于土壤。硝态氮是旱地土壤盈余氮素的主要存在形式,可以随水分运动而迁移,亦可以转化成N2O 而损失,对地表、地下水和大气造成潜在威胁。同时,土壤中大量盈余氮素的存在使氮肥利用率下降,增产效果不明显甚至降低产量,带来巨大的经济损失。本研究在北方传统冬小麦/夏玉米轮作栽培条件下,设置不同的施氮水平,采集冬小麦和夏玉米主要生育期的土壤和植物样品,测定土壤矿质态氮和植物养分,探索半干旱农田生态系统土壤剖面矿质态氮的运移规律及对作物的有效性,为优化施肥和种植制度,减少土壤硝态氮残留和向深层土壤运移提供理论依据。结果表明: 1、无论冬小麦,还是夏玉米,播前土壤矿质态氮(Nmin)对作物产量和氮肥效果有重要影响。较高的土壤Nmin 可以促进作物生长,使冬小麦和夏玉米对氮肥的利用率分别只有39%和5～22%左右,大部分肥料氮以Nmin残留于土壤剖面中,或以其他形式损失。从冬小麦/夏玉米整个轮作体系的土壤氮素平衡来看,氮肥增产效果和利用率均随施氮量的增加而急剧下降,土壤残留Nmin随施氮量增加而急剧增加,氮素表观损失在施氮量增至一定高度时呈现下降趋势。2、种植与休闲主要影响土壤水分含量和硝态氮累积量,对铵态氮累积无显著影响。种植玉米时土壤水分和硝态氮由于作物吸收而以向上运动为主,且被作物大量消耗,不会在土壤过量累积,可抑制淋溶作用发生。休闲则有利于水分在土壤剖面下层蓄积,进而增加了硝态氮向下层土壤的运移和累积。3、施氮量主要影响0-1m土层的硝态氮累积量,对1-2m土层硝态氮累积量和0-2m铵态氮累积量影响程度较小,不影响土壤硝态氮和铵态氮随生育期的动态变化趋势。生长前期硝态氮主要分布在0-60cm 土层中,随土壤水分下渗而逐渐向下层土壤移动,但其移动速度滞后于水分,最终未能移至1-1.2m 以下,硝态氮累积峰值随施氮量的增加而升高;铵态氮在土壤剖面中的累积量很小,施氮量对其剖面分布的影响只局限在拔节期,此后铵态氮在0-2m剖面分布比较均匀,不因施氮量和生育期而变化。4、施氮量影响夏玉米生长后期干物质累积和氮磷养分吸收及转移。不施氮时,夏玉米生长后期干物质合成和养分吸收受阻,收获时籽粒干物质和氮磷主要来源于灌浆期更多还原

【Abstract】 Application of nitrogen (N) is an important measure for increasing crop yields. Rational application of N fertilizer is of great significance in elevating crop yields and maintaining soil productivity. However, long-term and unreasonable input of N fertilizer may lead to a great deal of mineral-N (Nmin) residue in cropland soils. Nitrate-N is the main N form of fertilizer N residual in arid soil, it can move with water in soil profile and the runoff water over ground, and threaten the quality of ground and underground water. It can also be transformed to N2O gas and then pollute atmosphere. In addition, excessive N in the soil will decrease the recovery of N fertilizer by crops, even restrain crop growth and reduce crop yields. In this research, field experiments were carried out with test crops of winter wheat and summer maize, to study the balance and dynamics of mineral-N in dryland soils and its availability for crop at different N rates. We also discussed the accumulation and translocation of dry biomass, N, P and K in the vegetative parts of summer maize during late growth stages from grain-filling to harvest. The main purpose of this study was to optimize the management of N fertilizer in winter wheat and summer maize rotation, and reduce the residue of fertilizer-N and nitrate leaching in soils on dryland. The main conclusions are as follows: 1. The accumulation of mineral-N in preplant soil significantly affected crop yields and the efficiency of N fertilizer applied. Higher accumulation of mineral-N could lead to a decrease in fertilizer N recovery by winter wheat and summer maize, which was only 39% and 5～22%, respectively. Most of the fertilizer N remained in soil profile in the form of Nmin, or loss by other ways. The balance of soil N budget in the soil of winter wheat and summer maize rotation showed that fertilizer N use efficiency was decreased, and soil residual Nmin was increased with the increase of N rates. The apparent loss of fertilizer N tended to decrease at high N rates. 2. Cropping and fallowing significantly affected the accumulation and distribution of soil moisture and nitrate-N, but no effects was found on soil ammonium-N. When planting summer maize, soil moisture and nitrate-N mainly moved toward upper soil layers due to the crop transpiration and nutrient uptake, and nitrate-N residual in soil was largely decreased. In the contrary, storage of moisture in the subsoil was significantly increased by fallowing, and then nitrate was leached and residual in the subsoil layers with the downward moving soil water. 3. Fertilizer N rates remarkably influenced nitrate-N in 0-1 m soil layer, while nitrate-N in 1-2m soil layer and ammonium-N in 0-2m soil layers were not affected by N rates. In early growth stages of summer maize, nitrate-N was mainly distributed in 0-60cm soil layer, and then was gradually leached down, but not to the layers below 1-1.2 m at harvest. It was only during elongation stage that the N rates affected ammonium-N in soil profile, which was in a very small amount, evenly distributed in the 0-2 m soil profile, and not affected by application of N fertilizer at other stages. 4. The amount of N fertilizer significantly influenced the accumulation of dry matter and N and P uptake and their translocation in plant of summer maize during the late growth stages. The synthesis of dry matter and nutrient uptake was depressed when no N fertilization, and dry matter and nutrients in grain at harvest were found mainly transported from that accumulated in the vegetative parts of the plant before grain-filling. Appropriate application of N fertilizer could enhance synthesis of dry matter and uptake of N and P from soil during the late stages, and elevate the grain yield and N and P accumulation in grain. Over-application of N could not only decrease the grain yield, but also lead to a significant decrease in N and P uptake due to the relatively high accumulation of these nutrients in the stages before grain-filling. Thereafter, the capacity of nutrient uptake from soil by plant was decreased, and N and P in grain at harvest were also mainly from vegetative parts. Since the accumulation of K in grain at harvest was much less than that in vegetative parts, its translocation from vegetative parts to grain during the late growth stages of summer maize was not affected by N rates.更多还原