Effects of organic fertilizer extract on soil nutrient activation and use efficiency in cotton field

Objectives  Drip irrigation technology in Xinjiang is widely used and mature. With the application of water and fertilizer integrated fertilization methods, input of chemical fertilizers has greatly increased, and proportion of organic fertilizers has continuously decreased. In this study, combination organic manure with drip irrigation system was studied to explore activation of acidic nutrient solution by organic acid fertilizer extracts and the nutrient utilization efficiency of cotton.

Methods  In this study, the decomposed chicken manure was extracted with nitric acid (HN) and phosphoric acid (HP) at pH of 1 and drip-irrigated with chemical fertilizers. The organic fertilizer was used instead of the whole amount of phosphate fertilizer, 2/3 phosphate fertilizers and 1/3 phosphate fertilizers, the fertilization rates were 4950 L/hm², 3300 L/hm², 1650 L/hm², and nitrate and phosphoric acid were used as the control at the same fertilization rate and fertilization gradient with a pH of 1 (other nutrients were supplemented with chemical fertilizers, and the total nutrients of all fertilization treatments were same). In the flowering and boll stage (5 days after the fifth fertilization) and the boll opening stage (10 days after the eighth fertilization), the soil samples were taken at different distances from the dripper level 0–30 cm and vertical 0–60 cm in the cotton field. Samples were taken twice to determine soil organic matter, nitrogen, phosphorus, potassium and other effective nutrient content, and the activation of soil organic nutrients by the acidic organic fertilizer extract and the utilization efficiency of soil nutrients by cotton were studied.

Results  The results showed that: 1) Compared with the application of nitric acid and phosphoric acid extractants, the application of organic fertilizer extracts increased the soil organic matter content by 1.4% to 16.8%, while the corresponding application of the acidic extractant resulted in a 10.2%–25.5% decrease in soil organic matter content compared with CK. 2) The acidic organic fertilizer extracts under the replace of part of the chemical fertilizers increased the effective nutrient contents of 0–30 cm and 0–60 cm of vertical soil, especially for available phosphorus at 0–20 cm. The effect was obvious, and increased the absorption of the nutrients by crops. The amount of soil nutrients increased by 6.3% with the replacement amount of the chemical fertilizer was 1/3, but the difference was not significant. The replacement of 2/3 of the total amount of phosphate fertilizer and the replacement of all phosphate fertilizers increased soil nutrient by 35.3% and 58.1%, and the differences all reached significant levels. 3) Soil phosphorus and potassium were significantly activated by the acidic phosphate organic fertilizer extracts and the phosphoric acid extractant, and phosphoric acid organic fertilizer was more effective than the nitric acid. There was a negative correlation between pH of the organic fertilizer extracts and soil available phosphorus (–0.491*), and the organic matter content in the extracts had a significant positive correlation with soil available potassium (0.497*). 4) The application efficiency of nitrogen was the highest (53.1%) in the application of 4950 L/hm² nitric acid organic fertilizer extracts, and the phosphoric acid and potassium use efficiency of the phosphoric acid extractor treatment of 4950 L/hm² was the highest (28.9% and 344.8%).

Conclusions  As a new type of acidic organic fertilizer, organic fertilizer extracts can not only adapt to drip fertigation in Xinjiang, but also increase soil organic matter content and activate nutrients in Xinjiang calcareous soil, especially for the use efficiencies of phosphorus and potash fertilizers in 0–20 cm soil. Under the same amount of fertilization, the phosphorus and potassium activation efficiencies of phosphate organic fertilizer extract solution were higher than those of the nitrate organic extractant, and the highest yield was obtained when the phosphoric acid organic fertilizer extract solution was 3300 L/hm². The nutrient agronomic efficiency was the highest.