水氮配合对绿洲沙地农田玉米产量、土壤硝态氮和氮平衡的影响

在黑河中游边缘绿洲沙地农田研究了不同的水氮配合对玉米产量、土壤硝态氮在剖面中的累积和氮平衡的影响.结果表明,施氮处理较不施氮处理产量增加48.22%～108.6%,施氮量超过225 kg hm-2,玉米产量不再显著增加.受土壤结构影响土壤硝态氮在土壤中呈"W"型分布,即土壤硝态氮含量在0～20 cm、140～160 cm和260～300 cm土层均出现峰值,并随施氮量增加,峰值增高.在常规高灌溉量处理硝态氮含量峰值最高值出现在260～300 cm土层,节水25%灌溉处理硝态氮含量峰值最高值出现在土壤表层0～20 cm土层.在常规高灌溉量处理0～300 cm土层中200～300土层硝态氮累积量所占比例最高,介于27.56%～51.86%之间;节水25%灌溉处理在0～300 cm土层中100～200土层硝态氮累积量所占比例最高,介于32.94%～38.07%之间;表明低灌溉处理下土壤硝态氮在土壤浅层累积较多,而高灌溉处理使更多的硝态氮淋溶至土壤深层.与2006年相比,2007年不施氮处理0～200 cm土层土壤硝态氮含量和积累量均明显减少;而施氮处理变化很小,在低灌溉处理甚至表现出硝态氮含量和积累量增加,表明施氮是土壤硝态氮累积的主要来源,而灌溉则使硝态氮向土壤深层淋溶.0～200 cm 土层土壤硝态氮累积量平均介于27.66～116.68 kg hm-2、氮素表观损失量平均介于77.35～260.96 kg hm-2,和施氮量均呈线性相关,即随施氮量增加,土壤硝态氮累积量和氮素表观损失量均增加,相关系数R2介于0.79～0.99之间,相关均显著.随施氮量增加,玉米总吸氮量和氮收获指数增加,氮的农学利用率降低,而灌溉的影响较小.施氮量超过225 kg hm-2时,地上部植株氮肥吸收利用率和籽粒氮肥吸收利用率开始有降低趋势.所以,在沙地农田,节水10%～25%的灌溉水平和225 kg hm-2的施氮水平可以在避免水肥过量投入的基础上减少土壤有机氮淋溶对地下水造成的污染威胁.

Effects of nitrogen fertilization and irrigation rate on grain yield, nitrate accumulation and nitrogen balance on sandy farmland in the marginal oasis in the middle of Heihe River basin

A 2-year field experiment was conducted to determine the effects of nitrogen fertilizer rate and irrigation amounts on grain yield, nitrate accumulation and nitrogen balance on sandy farmland in the marginal oasis in the middle of Heihe River basin. Experimental treatments included three irrigation levels (conventional irrigation: 12000m3 hm-2, 10% (2006) or 12.5% (2007) water-saving irrigation, 20% (2006) or 25% (2007) water-saving irrigation) and five N rates (N1, 0 kg hm-2, N2, 150 kg hm-2, N3, 225 kg hm-2, N4, 300kg hm-2, N5, 375 kg hm-2). Nitrogen fertilizer application increased maize yield by 48.22%-108.6% compared with no nitrogen fertilizer treatment. However, maize yield, N uptake and use efficiency in total aboveground biomass and in grain did not increase significantly at N rates more than 225 kg hm-2. There were three peak values of NO-3-N content in the 0-20 cm, 140-160 cm and 260-300 soil layer as affected by soil texture and the peak values increased with increased N rates. Irrigation amount obviously influence NO-3-N accumulation in soil profile. The NO-3-N accumulation in the 200-300 cm layer was generally higher under conventional irrigation level than under the two water-saving irrigation treatments. However, NO-3-N accumulation in the 0-100 layer was higher under 20%-25% water-saving irrigation treatments than the other two irrigation treatments. The result indicated that more amount of NO-3-N was leached into deeper soil layers under conventional irrigation amount. The NO-3-N concentration in the 0-200 cm depth under no N fertilizer treatment was significant lower in 2007 than in 2006. The amount of NO-3-N accumulation in the 0-200 cm depth ranged from 27.66 kg hm-2 to116.68 kg hm-2 and the amount of apparent losses ranged from 77.35 kg hm-2 to 260.96 kg hm-2, which had significant and positive correlations with N fertilizer rates (R2: 0.788 and 0.987). With the increase of application rates, total N uptake and N harvest index increased, but N use efficiency decreased. It is concluded that 10%-25% water-saving irrigation and N fertilization with 225 kg hm-2 could improve irrigation water use efficiency and thereby reduce potential N leaching on sandy farmland.