Reduce N2O Emission By a New Fertilizer System for Maize-Cabbage Double Cropping Using Plastic Mulch Film.

Plastic mulching is a very common method in agriculture worldwide because the use of mulch films can improve product quality and yield by mitigating extreme changes, optimizing growth conditions and extending the growing season. Wisely use mulch films could reduce farmer’s labor and increasing nitrogen use efficiency by reducing fertilizer leaching. There are increasing evidences indicating the potential effectiveness of mulching on reducing N₂O bursts associated with intensive rainfall events. In this study, we designed a new fertilizer system, so-call “once fertilizer, double cropping”, with using controlled slow-release fertilizers and plastic mulch films. That is, fertilizer application only once in the beginning with different types of fertilizers to enable growing maize and cabbage through two seasons. We measured N₂O emission from soil covered with plastic mulch film under this new fertilizer system for maize-cabbage double cropping, and compared with the conventional management without use of slow-release fertilizers and plastic mulch films. The aim was to estimate the effectiveness of this new fertilizer system using mulching on reducing N₂O emission compared with the conventional fertilizer system.

The experiment was conducted on a cultivated Hydric Hapludand Andosol (WRB) in the Yatsugatake Highland in central Japan from May to October, 2014. Three treatments, three replicates with each 3×3 m² plot, were zero-N mulching soil (“O”, no fertilizer but with mulching films), chemical fertilizer applied to bare soil (“B” as conventional, total 500 kg N ha^-1 as Ammonium sulfate, i.e. 150+100 for maize and 90+160 for cabbage) and new fertilizer system (“M”, 90 kg N ha^-1 as Ammonium sulfate, 170 kg N ha^-1 as slow-release LP70 (70 days) and 90 kg N ha^-1as slow-release LPS120 (120 days) all applied in the beginning). Because M was only applied to mulching ridges and reduced the use of N application by 30% compared to B which applied to bare ridge and furrow. First crop maize was sown in early May and harvest in middle August. The second crop cabbage was transplanted in middle August and harvest in late October in 2014. GHG fluxes were then measured intensively with static chambers at eight conditions (each three chambers): BN (ridge), BW (furrow at B), MH (Mulching ridge with plant holes), MT (Mulching ridge without plant holes), MW (furrow at M), and unfertilized muching treatment (OH, OT, OW).

Mulching increased soil temperature especially at night, and resulted in a higher mean soil temperature in mulched ridge than bare soil during the experiment. Mulching kept the soil wetter and prevented a dramatic increase in soil moisture after intensive rainfall. N₂O emitted through mulch film (MT, OT) were extraordinary low. By the percentage of mulched ridge for Mulch_film (70%) and Mulch_hole (30%), and the percentage of ridge (47%) and furrow (53%), the weighted total N₂O (mg N m^-2) through the experimental period was calculated. Accordingly, total N₂O (mg N m^-2 period^-1) emitted from the conventional feritlized B plots (BN and BW) was 136.1±43.5 that much greater than from the new fertilizer system of mulching M plots (35.0±20.3). While N₂O emission from unfertilized mulching O plots was estimated as 17.2±9.6 mg N m^-2 period^-1. Although the results are still preliminary, this study highlights the potential effectiveness of this new fertilizer system with the use of mulch films on reducing N₂O emission.