Objectives Due to short fermentation time, the hyperthermophilic compost (HTC) is rich in nitrogen and small organic compounds. The effect of HTC application on the growth and yield of rice was studied for the safe and effective use of HTC.
Methods Two seasons of pot experiment were conducted using rice as tested crop. Five treatments were designed, including: zero-nitrogen control (N0); 100% chemical fertilizer (CF); and replacing 20% of the chemical N with conventional compost (CvC), raw fermented material (FRM) and hyperthermophilic compost (HTC). The growth, yield of rice, nutrient uptake and use efficiency and soil fertility were measured after harvest of rice.
Results Rice in HTC treatment had the highest grain yield, tiller number, grain number per ear, grain N uptake and N recovery efficiency. In 2016 and 2017, the rice grain yields in HTC were 25.8% and 32.8% higher than those in CF, and 22.4% and 16.5% higher than those in CvC. The number of grains per ear in HTC was 26.8% and 37.5% higher than that in CvC in 2016 and 2017; total K uptake in HTC was 45.5% and 33.9% higher than that in CvC in 2016 and 2017, respectively. The N recovery efficiency in both HTC and CvC treatments was significantly higher than that in CF, and that in HTC was significantly higher than in CvC in 2016. After rice harvest, the soil organic C content of HTC treatment was 14.4%–42.3% higher than CK and 4.12%–26.2% higher than CvC, respectively. HTC improved significantly soil organic C and mineral N than CvC, while the CvC was more conducive to maintaining higher soil available P content. The content of soluble organic C such as volatile organic acids and free amino acids in HTC was significantly higher than that of CvC, so the HTC treated soil had the highest average well color development (AWCD) and the strongest microbial activity. CvC treatment increased the utilization of carbohydrates and amines, while and the utilization of carboxylic acids and amino acids were enhanced by HTC treatment. There was a significant positive relationship between rice yield and soil EC, organic C, total N contents and AWCD values. Soil mineral N and plant K accumulation were significantly and positively correlated with soil total N and AWCD values.
Conclusions Although the HTC is less matured than CvC, the time needed in the process is significantly shortened and the temperature is higher to ensure more efficient disinfection of harmful microorganisms. At the 20% N replacement level, the application of HTC is more efficient to enhance rice yield and nitrogen recovery efficiency compared to CvC, which should be related to increased potassium utilization of rice and higher retention of soil mineral nitrogen and microbial activity.
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