Search

Using a microplate fluorimetric assay method, five fertilization treatments, i.e. no-fertilizer control (CK) , sole application of nitrogen (N), balanced application of nitrogen, phosphorus, and potassium fertilizer (NPK), application of pig manure (M), and combination of pig manure with balanced chemical fertilizer (MNPK) were selected to investigate the effects of different long-term fertilization regimes on the activity of five enzymes (β-1, 4-glucosidase, βG; cellobiohydrolase, CBH; β-1, 4-xylosidase, βX; β-1, 4-N-acetylglucosaminidase, NAG; acid phosphatase, AP) in a red soil sampled from Qiyang, Hunnan Province. The results showed that compared with CK treatment, N treatment had no impact on βG, βX, CBH, and NAG activities but reduced AP activity, while NPK, M and MNPK treatments increased the activities of all the five enzymes. Correlation analysis indicated that all the five enzyme activities were positively correlated with the content of nitrate (r=0.465-0.733) , the content of available phosphorus (r=0.612-0.947) , soil respiration (r=0.781-0.949) and crop yield (r=0.735-0.960), while βG, CBH and AP were positively correlated with pH (r= 0.707-0.809), only AP was significantly correlated with dissolvable organic carbon (r = -0.480). These results suggested that the activities of the measured enzymes could be used as indicators of red soil fertility under different fertilization regimes, but the five enzymes tested provided limited information on the degree of acidification induced by application of mineral nitrogen.

An investigation was made at a double-rice paddy field in the Qiyang Red Soil Field Experimental Station, Hunan Province, China to study the species and biomass of weeds growing in rice (Oryza sativa L.) growth season after 34-year application of sulfur (SO4(2-)) and chloride (Cl(-))-containing chemical fertilizers under the same application rates of nitrogen (N), phosphorus (P), and potassium (K). Long-term application of Cl(-)-containing chemical fertilizer resulted in the greatest species number of weeds and the highest biomass of floating weeds and wet weeds, compared with long-term application of SO4(2-) and Cl(-) +SO4(2-)-containing chemical fertilizers. In early rice growth season, the biomass of weeds after applying Cl(-)-containing chemical fertilizer was 51.4% and 17.6% higher than that after applying Cl(-) + SO4(2-) and SO4(2-)-containing chemical fertilizers, respectively; in late rice growth season, the increment was 144% and 242%, respectively. More floating weeds were observed after applying Cl(-) + SO4(2-) and SO4(2-)-containing chemical fertilizers, but few of them were found after applying Cl(-)-containing chemical fertilizer. The total dry mass of weeds and the dry mass of wet weeds were positively correlated with soil Cl(-) content (r = 0.764, P < 0.01 and r = 0.948, P < 0.01, respectively), but negatively correlated with soil SO4(2-)-S content (r = 0.849, P < 0.01 and r = 0.641, P < 0.05). Soil alkali-hydrolyzable N and available P, under the co-effects of soil SO4(2-)-S, Cl(-), and pH, had indirect effects on the total dry mass of weeds. By adopting various fertilization measures to maintain proper soil pH and alkali-hydrolyzable N and available P contents, increase soil SO42(-)-S content, and decrease soil Cl(-) content, it could be possible to effectively inhibit the growth of wet weeds and to decrease the total biomass of weeds in double-rice paddy field.