Effects Of Slow/controlled Release Compound Fertilizer On Soil Nitrogen And Enzyme Activity

It is one of the effective ways for people to increase fertilizer utilization rate and reduce environmental pollution by using slow/controlled release fertilizer (SRF), but it is difficult to popularize the SRF for lots of disadvantages, such as high cost, thinking much of nitrogen but less of phosphorus and potassium, latent pollution of some coated film and disregardfulness of relationships between soil property, plant nutrient characteristics and nutrient release. All of the reasons had seriously limited their applications in the field crops. In this paper, slow/controlled release compound fertilizer (SRCF) developed and produced by our own were employed to carry out effect of SRCF to soil nitrogen and enzyme activity during different stages. Pot experiments were also employed to explore the effects of SRCF on nitrogen transformation, enzyme activity of soil and growth of ryegrass. Objective of the research is to find a good method for the evaluation to functions of SRCF on fertilizing soil, growth of plant and attenuate environmental pollution. The main results were as follows.1. During the whole incubation period, contents of NH₄⁺-N in the SRCF treatment in both acid and neutral soil showed a trend which increased then decreased. The first peak value of contents of NH₄⁺-N in the SRCF treatment (14d) was a week later than that in the CCF treatment. In the middle and final term contents of NH₄⁺ -N in the SRCF treatment were higher than those in the CCF treatment2. Contents of NO₃^- -N increased in both the acid and the neutral soil and were lower in the CK treatment than those of other treatments. That in the CCF treatment was higher than those in both the CK and the SRCF treatment. The treatment SRCF1 was lower than the CCF1 treatment in the later period, while contents of NO₃^--N showed a higher level during the beginning period for the accession of raw material.3. Trends of the Alkali-hydrolysis N in the SRCF treatment showed a trend that increased then decreased, later increased and decreased again and the two peak values appeared respectively in the 21st and the 105th day. But the CCF treatment had just one peak value in the 21st day then came down.4. The contents of soil microbial nitrogen (SMBN) had same trend and peak value time with the available nitrogen. Peak time in the SRCF treatment came out at the 21st and 105th days. Those change traits of curves in the SRCF treatment were courses from fixation to mineralization then back again.5. The variations of fixed-ammonium in the two soils were consistent and changed less. The fixed-ammonium in the SRCF treatment was higher than that in the CCF treatment.6. Unease activities in the acid soil at early period of incubation varied from 26.72 to 57.68 NH₃-Nμg/kg in the SRCF1 treatment, lower than that in the CCF1 treatment (28.75-91.03NH₃-Nμg/kg) and kept higher in middle and final term. Unease activity in the SRCF2 treatment in the acid soil had the tendency of increase before the 21st day and was higher than other treatments after the 21st day. Unease activities in the neutral soil were from high to low then back again and were significantly higher than that in the acid soil. Unease activities in the SRCF1 treatment in the neutral were from 29.66-65.87NH₃-Nμg/kg , consistent with that in the acid soil and lower than that in the CCF1 treatment (31.66-114.0 NH₃-Nμg/kg) . After the 84th day, unease activities in the SRCF1 treatment were higher.7. Catalase activity in the SRCF treatment was higher than that of the CCF treatment and was approximately similar in the two soils. Catalase activity in the SRCF treatment in the neutral soil was lower than that in the acid soil.8. Unease activity was positive correlated with content of NH₄⁺-N in the fertilizing treatment in the two soils except the SRCF2 treatment in the neutral. The correlation coefficients in the SRCF treatment were lower than those in the CCF treatment. It meant that the SRCF was propitious to soil nitrogen conservation. In the acid soil, unease activity was extreme significantly correlative with the SMBN (r=0.8380**-0.8878**). In the neutral soil, unease activity in the SRCF1 treatment was significantly correlative with the SMBN (r=0.8515**) while the correlation coefficient in the SRCF2 treatment (r=0.8171*) was not significant than that in the SRCF1 treatment. Unease activity was negative correlated with fixed-ammonium but the relativity was not significant.9. Plant height, biomass and dry weight in the SRCF1-3 treatment were higher than those in the CCF1 treatment. Biomass and dry weight were lower in early period, higher in middle term than those in the CCF1 treatment and were equal in final term. Nitrogen nutrient contents and uptake increased with the rates of fertilizer application. Nitrogen nutrient content in the SRCF1-3 treatment was from 121.3 to 380.4 mg/pot and higher than that in the CCF1 treatment (83.58-443.6mg/pot). In the same nutrient ratio, the SRCF was more suitable for nitrogen absorption of ryegrass.10. Nitrogen nutrient uptake of ryegrass was negatively correlated to soil NH₄⁺-N and SMBN contents and positively correlated to NO₃^--N and fixed-ammonium. Relativity coefficient of nitrogen nutrient uptake and fixed-ammonium, catalase activity in the SRCF1 treatment was not significant.11. Contents of NH₄⁺-N, NO₃^--N and available nitrogen decreased along with the ryegrass growth. But contents of NH₄⁺-N, available nitrogen, SMBN, fixed-ammonium, unease activity and catalase activity in the SRCF1-3 treatment were higher than those in the CCF1 treatment in different stages, while contents of NO₃^--N were lower.