Combined long-term application of organic materials with nitrogen fertilizer in suitable amount could improve soil fertility and crop production profit in He-xi Oasis of Gansu Province

Objectives Irrigation agricultural area in He-xi Oasis, Gansu Province, is one of the important commercial maize production base in China. Study on the effects of different fertilization patterns on soil fertility and crop yield will provide a scientific basis for high efficient and sustainable agricultural production in the area.

Methods A long-term field experiment (1988-2009) under the base of application of P₂O₅ 150 kg/hm², except control, was conducted in irrigated desert soil. The 13 treatments included single application of farmyard manure 120 t/hm²(M), green manure 45 t/hm² (G), straw 10.5 t/hm² (S), N fertilizer 375 kg/hm² (N) and their combined application with each other as: 1/2MN, 1/2GN, 1/2SN, 1/2MG, 1/2MS, 1/2GS and 1/3MGN, 1/3MSN and 1/4MGSN. The soil organic carbon and available nutrient contents and the main soil enzyme activities were determined. Principle components analysis, cluster analysis and cost and economic returns were used to evaluate the soil quality and economic returns of different fertilization treatments.

Results Long term treatments of CK, N, NG, NS caused soil available K deficiency, and the corresponding decease was 16.59%, 39.37%, 25.04% and 23.31%, compared to those in 1988. The single application of M, G, and S or combined application with N could increase the contents of soil available N, soil available P, soil available K and soil organic matter (SOM) and soil enzyme activities (invertase, urease, alkaline phosphatase and catalase), and the contents of soil available N, P, K and SOM were in order of combined organic fertilizer application in high quantity > the combined application of low quantity organic fertilizer with low N > single N > CK. The single G or GN could increase the activities of invertase and urease, and the treatments of M, G and MN, GN could increase activities of alkaline phosphatase. The PCA and clustering analyses showed that the 13 fertilizer treatments can be divided into four categories according to the quality of soil: the first one was the high quantity organic fertilization including M, G and MG, the second one was the combined application of organic manure and N fertilizer including MN, MSN, MGN, GN, MS and MSGN, the third one was N, SN and S, and the last one was CK. Compared to CK, all the fertilization treatments could significantly improve crop yields, the crop yields were increased by 12.21%-235.4%, and the fertilizer contribution rates were in a range from 10.89% to 70.18%. The order of the crop yields was N > G > M > S, and the order of the crop yields was GN > MN > MSN > MGN > MG > SN > MSGN > MS. The organic fertilizer combined with application N fertilizer could obtain high yields. The cost and economic returns analysis showed that the single application of N fertilizer or organic fertilizer combined with N fertilizer could increase the net income.

Conclusions Through the analysis and comparison, single application of farmyard, straw and green manure needs huge amount of input to keep soil fertility and a certain level of yield in the long run, the cost is high and economic benefit is low as a result. Therefore, the combined application of suitable amount of nitrogen fertilizer with organic materials is recommended for the increase of the crop yields and economic efficiency, ameliorate soil health and improve soil ecological environment.