Effect of nitrogen fertilizer on dry matter accumulation and yield in wheat/maize/soybean intercropping systems

The effects of nitrogen fertilizer( on wheat 0,60,120,180,240 kg N /hm2,marked as WN 1,WN 2,WN 3, WN 4,WN 5; on maize 0,97. 5,195,292. 5,390 kg N/hm2,marked as MN 1,MN 2,MN 3,MN 4,MN 5; on soybean as SN 1,SN 2,SN 3,SN 4,SN 5) on dry matter accumulation( DMA) and grain yield( GY) of three crops in the wheat/ maize / soybean relay-cropping system were studied by field experiment in 2011 and 2012. Ⅰ) DMA and GY of the three crops increased significantly with N application( P 0. 01). Ⅱ) Wheat DMA and GY at the tillering stage( TS),jointing stage( JS),flowering stage( FS) and maturity stage( MS) increased with increasing rates of N. DMA at MS was the highest in treatment WN 4( 20610 kg/hm2) and GY at MS was the highest in treatment WN 5( 8176 kg/hm2) but there was no significant difference between WN 3,WN 4,and WN 5 treatments; Ⅲ) Maize DMA at the jointing stage( JS),flare opening stage( FS) and silking stage( SS) increased initially,then decreased with increasing rates of N, and was highest in MN 3. Maize DMA and GY at MS increased with increasing rates of N and they were both highest in treatment MN 5 with 13143 and 6976 kg / hm2,respectively,while there was no significant difference between WN 4 and WN 5. Ⅳ) Soybean DMA at FS and MS and GY initially decreased then increased with increasing rates of N,and its DMA and GY were the highest in SN 4( 5457 and 1977 kg/hm2,respectively),while there was no significant difference between WN 4 and WN 5. Ⅴ) Total GY and economic output( TEO) of the wheat / maize / soybean annual relay-cropping system rose with increasing rates of N and were the highest in the N 5 treatment with 11959 kg / hm2and 27288 yuan / hm2,respectively. The economic benefit of TEO and N input was highest in N 4 treatment with 25196 yuan / hm2and there was no significant difference between N 3,N 4,and N 5 treatments. The ratio of wheat,maize and soybean economic output to TEO of the system was 32%,55%,13%,respectively. So in the wheat / maize / soybean annual relay-cropping system maize is the top crop with wheat second and soybean third. Suitable N rates are 120 kg / hm2for wheat,195-292. 5 kg / hm2for maize,255-382. 5 kg / hm2for the annual system with proper N top application or with no application for soybean according to the growth.