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1978年以来我们连续测定了苜蓿地及其后作的养分变化动态,借以为确定苜蓿种植年限、开挖深度和小麦连种年数提供依据。现简报如下。从表1看出,苜蓿种植第一年可在土壤中累积氮素18.6斤,第二年54.5斤,第三年增加到92.1斤,第四年由于根瘤老化,固氮能力衰退,累积量下降,变为78.6斤。除了土壤微生物活动的消耗及氮素的分解损失外,每年土壤增加的氮素约占累积量的50％左右;有机质和氮素有相似的规律;磷素总的是下降趋势;速效钾变化不太大。因此, 一、苜蓿不同种植年代耕层养分变化状况苜蓿有根瘤,能固定气态氮,增加土壤氮素营养。由于种植年代长短不同,给土壤增加的氮量也不一样(表1)。
Since 1978, we have continuously determined the dynamic changes of alfalfa land and its nutrients, which will provide the basis for determining the planting time of alfalfa, the depth of excavation and the annual number of wheat. Now briefing as follows. As can be seen from Table 1, alfalfa can accumulate 18.6 kg of nitrogen in the soil in the first year, 54.5 kg in the second year and 92.1 kg in the third year. In the fourth year, due to the root nodule aging, the nitrogen fixation capacity declined, Into 78.6 pounds. In addition to the consumption of soil microbial activities and the loss of nitrogen decomposition, the annual increase of soil nitrogen accounted for about 50% of the cumulative amount; organic matter and nitrogen have similar rules; the total phosphorus is the downward trend; Too big. Therefore, alfalfa nutrient levels in different growing years alfalfa nodules, can fix the gaseous nitrogen, increase soil nitrogen nutrition. Due to the different planting years, the amount of nitrogen added to the soil is also different (Table 1).