旱地土壤的合理施肥——Ⅹ.旱地与灌区不同氮肥用量的效果

Rational Application of Fertilizers on Drylands Ⅹ. Effects of different N rates on yield increases for Dryland and irrigated land

氮肥用量严重地影响着氮肥肥效。用量不足,难以高产;用量过高,也会减产。合适的氮肥用量与土壤的供水情况和土壤的NO^-_3—N含量有密切关系。 无灌溉条件的旱地,不管土壤供氮水平高低,小麦的最高产量在250—330kg;有灌溉的地方可达400kg以上。1m土层中NO^-_3—N含量低时,在一定范围内小麦产量随施氮量直线上升;含量高时,则无这种关系,甚至施氮后还有减产现象。旱地以亩产300kg为指标,1m土层中的NO^-_3—N为3kg左右时,需亩施4kgN;为5—8kg时,需亩施2kgN;含量更高时,则可不施;水地以亩产400kg为指标,NO^-_+—N为3kg左右时,需亩施8kgN,为7—8kg时,需亩施4kgN,高于10kg,可不施。

Applying rates of N fertilizers greatly affect N-firtilizer efficiency. High yield will not beable to reach if application of N fertilizer is not sufficient. However, too high rates of N fertilizerwill cause yield decrease. Rational rates of N fertilizer are closely related with soil water supplyand NO_3^- -N contents at the depth of 0 to 100 cm.On drylands, no matter what the. NO_3^- -Ncontents are, the maximum yields of wheat reached only 250～330 kg/mu. However, on the ir-rigated lands, yiclds could reach more than 400 kg. When NO_3^- -N at 100 cm depth is low,wheat yielde increased linearly with increase of N fertilizer rates within a certain range. In con-trast, there was no such relationships, and high rates may even cause yield decrease when soilNO_3^- -N content was high. The index for application of N fertilizer rates is proposed as follows:on drylands with objective yield of 300 kg/mu, applying 4 kg N for soil with 3 kg NO_3^- -N, 2kg N for soil with 5～8kg NO_3^- -N, and none for soil with more NO_3^- -N; on irrigated landswith objective yield of 400 kg, applying 8 kg N for soil with 3 kg NO_3^- -N, 4 kg N for soil with7～8 kg no_3^- -N, and none for soil with more than 10 kg NO_3^- -N.