Abstract:

[Objective] The aims of the present study were to fully exploit the application potential of cattle manure as organic fertilizer and to avoid potential heavy metal hazards to soil-crop ecosystem from excessive application of cattle manure. [Method] Five treatments were set up according to the different application ratios of cattle manure organic fertilizer and chemical fertilizer: a blank control （CK）, the single application of cattle manure organic fertilizer （CD）, the single application of chemical fertilizer （CF）, the combined application of cattle manure organic fertilizer with chemical fertilizer （DF1） at the ratio of 1∶1, and the combined application of cattle manure organic fertilizer with chemical fertilizer （DF2） at the ratio of 2∶1. Pot experiments were conducted using soil and silage maize as research subjects. The mass fractions of various forms of heavy metals of copper （Cu） and zinc （Zn） in soil under different fertilization treatments were measured and calculated. The correlations between the distribution rate of available Cu and Zn and soil pH value, organic carbon mass fraction were analyzed. The Cu and Zn contents in different parts of silage maize were compared. [Result] Combined application of cattle manure organic fertilizer with chemical fertilizer had significant （P<0.05） impacts on the total mass fractions and mass fractions of different forms of Cu and Zn in the soil. The application of cattle manure organic fertilizer promoted the transformation of residual form Cu to exchangeable form. The distribution rates of exchangeable Cu in CD and DF1 treatments increased from 15.86% in CK to 28.12% and 28.13%, respectively. Compared with CK, DF2 treatment had the largest increase in distribution rate of exchangeable Cu at 42.02%. The distribution rates of residual Zn in CD and DF1 treatments decreased from 53.40% in CK to 39.27% and 38.40%, respectively. In comparison with CK, the distribution rate of residual Zn in DF2 treatment decreased to 24.33%, which had the biggest change range. After the combined application of cattle manure organic fertilizer with chemical fertilizer, the soil pH value and organic carbon mass fraction had an upward trend. Among them, the soil organic carbon mass fraction had positive correlation with the distribution rates of available Cu and Zn in the soil, and the correlations reached extremely significant （P<0.01） and significant （P<0.05） levels, respectively. Furthermore, the distribution rate of soil available Zn was significantly （P<0.05） correlated with the change trend of soil pH value, while the correlation between the distribution rate of available Cu and soil pH value was not significant （P>0.05）. Compared with CK, the application of cattle manure organic fertilizer increased the contents of Cu and Zn in maize plants by 45.50% to 115.38% and 44.99% to 93.29%, respectively. [Conclusion] In addition to improving the physical and chemical properties of soil, the combined application of cattle manure organic fertilizer with chemical fertilizer activated the heavy metals of Cu and Zn in the soil, enhancing the heavy metal enrichment ability of the silage maize. Therefore, when applying cattle manure organic fertilizer, the appropriate application rate should be determined strictly following the soil testing and formula fertilization to limit the contamination risk of heavy metals in the soil environment and the feeding risk of silage maize.

Key words: cattle manure organic fertilizer, combined application, heavy metal form, silage maize, enrichment