Abstract
Nitrogen utilization efficiency (NUE) plays an important role in evaluating crop production and production efficiency of recycling agriculture. In this study, the NUE was systematically investigated in two recycling agriculture modes, in order to accelerate the application of “Rice/Pearl millet -Mushroom-Cabbage” in the southern China. Two recycling agricultural modes were the “Rice-Mushroom-Cabbage” marked as mode R, whereas, the “Pearl millet-Mushroom-Cabbage” marked as mode P. Each recycling agricultural mode included three sectors, namely, three experiments. The first sector was that the 15N-labeled urea was applied as the nitrogen fertilizer to rice and pearl millet (Pennisetum americanum×P.purpureum), marked as Ⅰ sector. The second sector was that two straws harvested from rice and pearl millet of Ⅰ sector were used as substrates to cultivate oyster mushroom, marked as Ⅱ sector. The third sector was that mushroom residues were applied as fertilizer to cultivate cabbage, marked as Ⅲ sector. A 15N tracer technique was used to evaluate the NUE in two recycling agricultural modes in three sectors. The results indicated that the distribution of 15N in the rice grain was 57.75%, greater than that of straw, while, that in the first harvest pearl millet was the highest, accounting for 58.94%. The highest nitrogen distribution in Ⅰ sector of mode R was in soil, followed by the aboveground plant and root, while that of mode P was observed in plant, followed by the soil and root. The order of nitrogen distribution in two modes was ranked as: the mushroom residues > oyster mushroom in Ⅱ sector, and soil > plant > root in Ⅲ sector. The highest NUE was observed in Ⅰ sector of R and mode P, which were 23.44% and 43.34%, respectively. The second was in Ⅱ sector, and the lowest was observed in Ⅲ sector. There were significant differences for the NUE in three sectors of mode P, and the NUE in Ⅰ sector of mode P significantly increased 19.23% and 92.97%, compared with the Ⅱ and Ⅲ sector, respectively. The highest nitrogen residue rate (NRR) was observed in Ⅱ sector of R and mode P, which were 43.48% and 50.74%, respectively, followed by that in the Ⅲ sector, and the lowest was in Ⅰ sector. The NUE of mode P significantly increased 84.90%, 69.31% and 47.29%, compared with mode R in Ⅰ, Ⅱ, and Ⅰ+Ⅱ+Ⅲ sector, respectively. Meanwhile, there was no significant difference for the NUE between mode P and mode R in the Ⅲ sector. The NRR of mode P was lower than mode R in Ⅰ sector. There was an opposite performance in Ⅱ sector, and a higher NRR was observed in mode P. The nitrogen loss rate (NLR) of mode P was lower than that of mode R in Ⅱ sector, while, there was no significant difference for the NLR between two modes in Ⅰ and Ⅲ sector. The percentage of N derived from 15N fertilizer (Ndff) of mode P was higher than that of mode R in Ⅰ sector, and there was no significant difference for Ndff between two modes in Ⅱ and Ⅲ sector. The NUE of two recycling agriculture modes was improved after adding sectors, compared with the solo rice/pearl millet planting, the 15N accumulation in the aboveground plants of recycling agriculture in mode R and mode P increased from 63.50 and 112.30 mg to 115.33 and 169.89 mg, and the NUE increased from 22.29% and 39.41% to 40.48% and 59.62%, indicating the increases of 18.19 and 20.21 percentage point, respectively. The NUE of pearl millet was higher than that of rice, and the utilization efficiency of oyster mushroom assimilating nitrogen from pearl millet substrate was also higher than that from the rice straw substrate. Simultaneously, where the NUE, NLR and Ndff of “Pearl millet-Mushroom-Cabbage” mode behaved better than that of the “Rice-Mushroom- Cabbage” mode. Therefore, it infers that the recycling system of “Pearl millet-Mushroom-Cabbage” was fit for the application in south China.
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