自1964年郊区发展三熟制以来,化肥用量急剧增长,群众较普遍地反映,作物产量虽逐年提高,但土地似“越种越瘦”。于是不少人认为,土壤对化肥胃的口越来越大。“化肥胃口增大”说,大体有二层意思。一是化肥的增产效率低。根据试验和调查,化肥对稻麦粮食作物增产效率,三熟制后的确明显降低。以硫酸铵和碳铵为例,每斤化肥增产的粮食数,平均降低一斤左右,增产效率平均为两熟制阶段的55～73％。二是对化肥的需求量越来越大。尽管郊区耕地的化肥施用水平,从1964年前后的60斤/亩左右(折合养分约10斤)增长到近五年的296斤/亩(折合养分约44斤),但仍有不足之感,缺肥仍较普遍。这 Since the development of the three-cropping system in the suburbs in 1964, the amount of fertilizer used has risen sharply and the general public has generally reflected that while crop yields have been increasing year by year, the land has become more and more lean in scale. So many people think that the soil on the mouth of the stomach fertilizer is growing. “Fertilizer appetite increases,” said that there are two layers of meaning. First, fertilizer production efficiency is low. According to the tests and surveys, the fertilizer production efficiency of rice and grain crops is obviously reduced after the three-cropping system. Ammonium sulfate and ammonium bicarbonate, for example, the number of grains per kilogram of chemical fertilizer production, down an average of about a pound, the average yield efficiency of two to the cooked stage of 55 to 73%. Second, the demand for chemical fertilizers is growing. Although the level of chemical fertilizers in suburban cultivated land increased from about 60 kg / acre (about 10 kg) before and after 1964 to 296 kg / acre (equivalent to about 44 kg) in the recent five years, there was still a sense of inadequacy. Missing is still more common. This