Effects of black soldier fly frass on rice growth and soil physical and chemical properties

Objectives Black soldier fly frass was obtained by biotransformation of animal dung using black soldier fly larvae. It had high content of organic matter and nutrients. We studied the effects of black soldier fly frass as organic fertilizer on crop growth and soil fertility improvement.

Methods Pot experiments were conducted using rice as tested crop. The insect frass were applied in ratio of 0 (CK), 2% (T1), 4% (T2), 6% (T3), and 8% (T4) of the pot soil weight. Rice was planted for two consecutive years after one fertilization. The plant height and yield of rice, the rice leaf enzyme activity, N, P, K content, soil nutrient index and soil enzyme activity were analyzed.

Results In first year of fertilization (2018), the plant height and yield of T2 treatment were the highest, and were 5.8% and 43.7% higher than those of CK, while T4 treatment had the lowest plant height and yield, which were 8.0% and 20.0% lower than those of CK. In the second year (2019), the plant height and yield of rice increased with the increase of insect frass application rate, and compared with CK, the plant height and yield of fertilization treatment increased by 11.5%−33.5% and 33.9%−195.5%, respectively. The insect frass increased the activities of SOD, POD and CAT in rice leaves and the contents of N, P and K in rice in two years. The insect frass also increased the soil pH from 6.46 and 6.51 to 7.13 and 7.14, respectively in two years, increased organic matter content by 7.1%−32.5%, EC value by 13.6%−99.9%, ammonium N by 25.2%−195.4%, available P by 45.7%−312.0%, and readily available K by 1.7−20.1 times. The activities of urease, phosphatase and sucrose in soil were increased by 13.1%−109.5%, 14.5%−45.4% and 25.2%−286.5% , respectively.

Conclusions The application of black soldier fly frass is proved of effective in improving soil fertility. Reasonable application amount promoted the growth and yield of rice in current and following seasons. Therefore, black soldier fly frass is promising to be used as an organic fertilizer in crop production and soil fertility maintenance.