为了探索保护地土壤供肥特点和氮、磷、钾肥施用效应，以生菜为供试作物，在北京顺义杨镇松各庄布置了“3414”平衡施肥试验。结果表明，施氮210 kg•hm-2、磷（P2O5）90 kg•hm-2和钾（K2O）150 kg•hm-2时，生菜产量最高，达59967.0 kg•hm-2。施磷、钾肥对产量无显著影响，揭示大棚土壤并不缺磷钾。回归分析表明，氮164 kg•hm-2，为最佳经济施肥量，此时生菜产量为59115.8 kg•hm-2。该田块肥料利用率低，钾最高只有12.0%，氮肥最高利用率为5.9%，而磷肥最高也只有5.1%左右。在氮、磷、钾养分平衡指数中最高的钾只有1.73，最低的磷只有0.27。生产实践中应及时监测土壤养分状况，合理施肥，避免资源浪费。

For studying on soil nutrient supply status under greenhouse and effect of N,P,K fertilization on lettuce, a balance fertilization experiment with “3414” design was carried out on a facility field in Songgezhuang village, Shunyi district of Beijing. The results showed that when N was 210 kg•hm-2, P2O5 was 90 kg•hm-2 and K2O was 150 kg•hm-2, the yield was 59967.0 kg•hm-2, and the phosphorus and potassium fertilizer had no significant influence on lettuce yields, demonstrated that the experimental soil was not lack of available phosphorus, and potassium. Regression analysis indicates that the dose of 164 kg•hm-2 N can give the best economic yield of 59115.8 kg•hm-2. The result also showed that the fertilizer recoveries by lettuce were very low, in which the highest value was potassium with only 12.0%, nitrogen was 5.9% and phosphorus was no higher than 5.1%. In the balance indexes of nutrition for N, P, K, the highest index for K was only 1.73, and the lowest one for P was 0.27. These results also indicated that the recoveries of chemical fertilizer nutrient were very low, so the soil nutrition needs to be monitored regularly, and fertilizing carefully, avoiding from resources waste.