Effects of Combination of Organic Fertilizer and Rotational Tillage Patterns on Nitrogen Migration and Transformation in Fluvo-Aquic Soil in Northern Henan Province

Based on the long term tillage experiment, this study investigated the effects of combination of rotational tillage mode and fertilization on nitrogen migration and transformation, crop growth in fluvo-aquic soil in the northern Henan province, aiming to select the optimal agricultural management in this area.

The long term tillage experiment with two-factor split-plot design was carried out. Fertilization with manure or not was the main factor and tillage mode as the subfactor. Four rotational tillage modes were set as: (1) Continuous rotary tillage (RT-RT-RT); (2) Deep tillage-rotary tillage-rotary tillage (DT-RT-RT); (3) Deep tillage-rotary tillage-shallow rotary tillage (DT-RT-SRT); (4) Deep tillage-shallow rotary tillage-shallow rotary tillage (DT-SRT-SRT). The soil nitrogen forms, enzyme activity, crop nitrogen utilization, and yield were determined and analyzed.

Compared with RT-RT-RT with mineral fertilizer (NPK), all the nitrogen forms content were increased under DT-RT-SRT with manure (NPKM) in the 0-40 cm soil layer. Therein, total nitrogen (TN), nitrate nitrogen (NO₃^--N), and ammonium nitrogen (NH₄⁺-N) content increased by 25.0%-49.1%, 42.8%-140.0%, and 4.6%-125.6%, respectively. In the 0-40 cm soil layer, the bulk density (BD) under NPKM was lower (0.3%-15.7%) than that under NPK, soil porosity (SR) increased by 8.5%-18.2% under DT-RT-SRT relative to RT-RT-RT. In the 0-20 cm soil layer, compared with the NPK+RT-RT-RT, soil urease, sucrase, and alkaline phosphatase activities increased by 4.0%-53.3%, 22.7%-71.3%, and 4.2%-57.2% under NPKM+DT-RT-SRT, respectively. The crop yield was increased under the treatment with combination of manure and rotational tillage modes. Compared with NPK, nitrogen accumulation in wheat increased but its nitrogen uptake and utilization reduced under NPKM condition. Compared with NPK+RT-RT-RT, in wheat season, the nitrogen accumulation in above-ground biomass, grain, and harvest index increased by 87.2%, 91.4%, and 30.3% under NPKM+DT-SRT-SRT, respectively. However, nitrogen use efficiency (NUE) and partial factor productivity decreased by 10.6% and 33.1%, respectively, while the nitrogen uptake efficiency in the subsequent maize season increased by 22.1%. Rotational tillage treatments reduced the apparent loss of nitrogen, with the best effect exhibiting under DT-SRT-SRT treatment. Compared with NPK, NPKM significantly increased crop nitrogen uptake and soil nitrogen residue, but the apparent nitrogen loss increased. The correlation analysis indicated, in the 0-40 cm soil layer, during wheat and maize seasons, BD was negatively correlated with crop yield, TN, NO₃^--N, NO₄⁺-N, and other indicators content, while the nitrogen content was positively correlated with urease, sucrase, alkaline phosphatase activity, harvest index, and other indicators. Principle component analysis showed the effect of fertilization on soil physical, chemical and biological properties was more markable than that of tillage mode, and this effect was larger during wheat season than that during maize season.

In summary, the combination of manure and rotational tillage improved soil physical structure, increased the content of various forms of soil nitrogen, enhanced the soil enzymes activity, promoted nitrogen accumulation in plants, and increased crop yield, significantly reduced the apparent loss of soil nitrogen, which was conducive to the nitrogen balance of the soil. Therein, NPKM+DT-RT-SRT demonstrated the most effective improvement in both soil and crop quality. NPKM+DT-SRT-SRT exhibited the best improvement effect on the nitrogen efficiency index and the highest nitrogen utilization efficiency. Therefore, they were recommended as a suitable agricultural management in fluvo-aquic soil in the northern Henan Province.