Objective We investigated the effects of cattle manure addition on fluvo-aquic soil labile organic nitrogen fractions and soil enzyme activities by using indoor incubation method, to reveal the mechanisms of cattle manure on soil organic nitrogen fractions in different fertilization treatments. This research not only provides theoretical basis for rational application of organic fertilizer and sustainable development of agricultural ecosystem, but also is beneficial to reusing agricultural resources and maximizing their benefits.
Method An indoor incubation was used to study changes of soil liable organic nitrogen fractions (microbial biomass nitrogen (MBN), dissolved organic nitrogen (DON) and particulate organic nitrogen (PON)) and soil enzyme (α-1,4-glucosidase, AG; β-1,4-glucosidase, BG; β-1,4-xylosidase, BXYL; cellobiohydrolase, CBH; phosphatase, PHOS; peroxidase, perox; and phenol oxidase, phenox) activities in a long-term fertilizer experiment established in 1986 in Yucheng site, Shandong province, China. There were 4 treatments in the long-term fertilizer experiment, including no-fertilizer treatment (CK), standard rate of organic manure treatment (OF), standard rate of mineral fertilizer (CF), and half-standard rate of organic manure plus half-standard rate of mineral fertilizer treatment (OCF).
Results Firstly, regardless of cattle manure addition, the contents of total nitrogen (TN), DON and PON in different fertilized soils were increased or had no significant differences during the incubation time. Secondly, the contents of total nitrogen (TN), DON and PON in different fertilized treatments with cattle manure addition were increased by 5.43%–15.49%, 5.83%–69.42% and 9.75%–42.29%, respectively, after incubation, while the content of MBN was decreased by 16.91%–62.10%. Fertilization, cattle manure addition and their interactions had significant effects on soil enzyme activity (P < 0.05). Regardless of cattle manure addition, the activity of soil oxidase enzymes (perox and phenox) in all fertilizer treatments was significantly lower than that of no-fertilizer treatment, but the activities of soil hydrolytic enzymes in all fertilizer treatments presented different trends. Without cattle manure addition, the activities of soil hydrolytic enzymes except BG significantly increased in long-term fertilizer treatments; compared with CK, the activities of BXYL and CBH in CF increased by 208% and 180%, respectively. With cattle manure addition, compared with CK, the activities of BG and CBH in OF increased by 201% and 308% respectively. According to the redundancy analysis (RDA), the dominant environmental factor of TN and soil labile organic nitrogen fractions affecting soil enzyme activities was DOC without cattle manure addition. However, the dominant environmental factors were changed to TN and DOC with cattle manure addition.
Conclusions The contents of MBN, DON and PON were significantly correlated with soil TN under long-term fertilization regimes. With cattle manure addition, the contents of TN, DON and PON increased in different fertilized treatments, but the content of MBN significantly decreased. Soil enzyme activities in different fertilized treatments were significantly different, and cattle manure addition changed the dominant factors of TN and soil labile organic nitrogen fractions affecting soil enzyme activities in different fertilization regimes.
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