| Alfalfa (Medicago sativa L.) is an important high quality forage crop with ecological and economic benefits. With rapid development of animal husbandry and re-adjustment of cropping systems in China, alfalfa is receiving more and more attention. Nitrogen, phosphorus (P) and potassium (K) are essential nutrients for normal plant growth, but also important components in alfalfa forage quality evaluation. Therefore, the status of P and K nutrition has significant effects on alfalfa yield and quality. Although there are research reported in the literature on effects of P and K on yield and quality of alfalfa, little work has been done to study the effects of P and K nutrition and inoculating rhizobia on alfalfa yield and quality in Xinjiang.In 2003, field experiment was conducted in Changji County of Xinjiang province to determine the effect of 3 levels of P and K and their combinations on growth yield and quality of alfalfa. Furthermore pot experiment was also conducted in Xinjiang Agricultural University Trial Field to study 3 levels of P and K and their interactions on yield and quality of alfalfa. In 2004, the above 2 experiments were continued, and additional field experiment with 3 genus rhizobia was conducted in Xinjiang Agricultural University Trial Field to study the influence of inoculating rhizobia on alfalfa yield and quality. In 2005, the above 3 experiments were continued, and additional field experiment 4 genus rhizobium was conducted in Xinjiang Agricultural University Trial Field to validate the rhizobium experiment. The results and main conclusions are as following:一,Results from pot experiments indicated that forage yield was increased with increase of application rates of P and K until to optimal level, over which, further increase of P and K application rate resulted in negative effects on plant growth and yield. Significant interactive effects of P and K on alfalfa plant growth and yield were also found. The proper quantities were phosphorus fertilizer 5.089g/l0kg soil and potassium fertilizer 2.584g/10 kg soil. When the yield reach to the highest the optimum ratio of N: P2O5: K2O is 1: 0.264: 1.434. Based on three-year- yield of the alfalfa, we can obtain a fertilizer response function, its optimum fertilization and the yields in three years with the function y=18.4596e0.4359x(R=0.9984). Proper use of P and K fertilizer progressive absorption of N, P and K alfalfa plant, but excessive application of P and K fertilizer had negative effects on absorption of alfalfa forage. Significant interactive effects of P and K on N absorption alfalfa were also found. The proper quantity of phosphorus fertilizer and potassium fertilizer were 4.452g/l0kg soil and 2.365g/10 kg soil. Significant interactive effects of P and K on P absorption alfalfa were also found. The proper quantity of phosphorus fertilizer and potassium fertilizer were 5.990g/l0kg soil and 4.354g/10 kg soil.二,Field experiment was conducted to investigate different amount of fertilizer on growth and yield and nutrition absorption of two kinds of alfalfa crop in maroon calcium soil.Based on three years plant heights of two kinds of alfalfa, we can obtain the highest increased rate (HIR) of plant height, maximum period of HIR and the average growth rate by using the logistic equation y=k/(1+aebx). Result indicated that the optimum rate of P and K to obtain the highest yield, the highest increase rate of plant growth and its maximum period, and highest average growth rate was treatment 1 for Medicago varia Martin.cv.Xinmu.No.1 and treatment 3 for Medicago sativa L.cv.Xinjiang Daye.Based on three-year-yield of two kinds of alfalfa, we can find that the yield of Medicago varia Martin.cv.Xinmu.No.1 reached to the highest was treatment 1, its optimum ratio of N: P2O5: K2O is 1:0.326:1.999; the yield of Medicago sativa L.cv.Xinjiang Daye reached to the highest was treatment 3, its optimum ratio of N:P2O5:K2O is 1:0.233:1.711.
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