| Drought and water shortage is the main limiting factor on the arid-area of agricultural production In the Northwest Loess Plateau. Thus, how to improve the crop yields meanwhile maintain the soil fertility and soil quality is the key issues of regional agricultural development. This paper is based on a long-term fertilization experimental station which was established in 1979 at Gaoping village of Pingliang, Gansu province, being used for studying the long-term effects of different fertilization (N:nitrogen; NP:nitrogen and phosphorus; SNP:straw together with the nitrogen and phosphorus; M:manure; MNP:manure with nitrogen and phosphorus; CK: unfertilized control.) on soil enzymatic activities and soil physical and chemical properties. And we also discussed the succession of law of them during physiological stages of wheat crop, as well as the correlation of between them and each soil enzymes. This can provide a scientific basis for further discussion soil enzymes an sensitive index to fertility and establish a reasonable fertilizer management to improving soil quality and achieving given a theoretical base for sustainable use of soil. The main results were abstracted as follow:1. Effect of long-term fertilization on soil physical and chemical properties Our analysis results show that farm yard manure and combinations of inorganic fertilizer significantly increased the amount of soil total P, but application of straw or nitrogen was not. Application Fertilizer increased the mean values of available P except for the N treatment and the highest value was found in MNP treatment. Total N varied little across treatments and the highest value was also recorded in MNP treatment. Fertilization did not significantly increase the total N content except MNP, on the contrary SNP, NP and N treatments were lower than CK. Application of farmyard manure was more pronounced and effective in enhancing the soil organic C and higher than application of straw or inorganic fertilizer. Combined application of N and P was also have a significant increase and higher than single N amended treatment and control. The pH values ranged from 7.25 to 7.49, with that of the unfertilized control soil around the lowest at pH 7.25. Manure and fertilizer application increased soil pH significantly, and the values were less in the different fertilized treatments than in manure treated plots. Soil moisture slightly changed between different treatments with long-term fertilizer management.Our study also revealed that soil nutrient content and soil pH also differed by growth stage of the wheat. The highest total P was found at maturity, followed by the dough and jointing stages. Available P did not change significantly during crop growth. Total N and organic C were highest in the soil during the dough stage of the wheat crop followed by the jointing and maturity stages. The mean values of soil pH and soil moisture were significantly different under different crop stages, in the following order:dough> maturity> jointing and maturity> jointing> dough, respectively. All soil properties except soil pH and moisture declined with the soil depth, suggesting that soil depth does affect some soil characteristics.2. Effect of long-term fertilization on soil enzymatic activitiesSoil enzyme activities were strongly influenced by the long-term application of organic and inorganic fertilizer at different stages of wheat growth and at different soil depths, as evidenced by highly significant F-values (p<0.0001) for the treatments, stages, depths and their interaction. In the different fertilized treatments, dehydrogenase followed the order MNP>M>NP>SNP>CK>N. P-deficiency was pronounced have an effect on soil dehydrogenase. Fertilization can significantly improve the urease activity and farmyard manure amended treatments was more effective than straw and inorganic applied. Alkaline phosphates was enhanced by applying organic manure, however, there is no significant effect related to control although the higher values were found in mineral fertilizer applied treatments. Organic manure and combined of nitrogen and phosphorus amended significantly contributed the soil invertase activity but was no difference between them. Single nitrogen applied was no pronounced effect on invertase. Glomalin content was significantly influenced by organic manure applied and mineral fertilizer was not. In a word, the activities of all enzymes were generally higher in the fertilized than in the unfertilized treatments, and the application of organic fertilizer produced higher activity than addition of inorganic fertilizer treatments, although there were some exceptions to this trend.Soil enzyme activity varied with the growing stages of wheat. In generally, the highest value was at the dough stage of the wheat crop followed by the jointing and maturity stages, although differences were only significant for urease and glomalin. We found highly significant differences in soil enzyme activity at different depths for all enzymes; enzyme activity declined with soil depth (P<0.001).3. The relationship of soil enzyme and physical and chemical propertiesThere was a close positive correlation between dehydrogenase and available P (R2=0.749). Soil organic C was correlated with all enzymes measured. Urease had a strong positive relationship with pH value (R2=0.719). Meanwhile close positive relationships were also found between dehydrogenase, alkaline phosphatase, invertase, and glomalin.3.4 Effect of long-term fertilized on wheat yieldFertilizer application, both organic and inorganic, significantly increased the amount of wheat yield, and average values for wheat yield ranged from 1733.38kg ha-1 for the control to 5623.34kg ha-1 for MNP. The balanced application of nutrients (MNP, SNP and NP) led to a more pronounced effect on the size of the wheat yield than single fertilizer amended (M and N). The yield data clearly demonstrate the superiority of the integrated use of farmyard manure and mineral fertilizers, which can be to ensure that income while reduce the amount of nitrogen fertilizer. And this is both the economic and ecological benefits of the application system.
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