Study on yield and differences of nutrient absorptions of maize in wheat/maize/soybean and wheat/maize/sweet potato relay intercropping systems

To analyze and compare the differences of maize yields, nutrient absorptions and soil nutrients of the cultivated layers between the intercropping systems, wheat/maize/soybean and wheat/maize/sweet potato, a three-year field experiment designed with single-factor at random was conducted in two main maize producing areas in Sichuan, Shehong in the middle and Yaan in the west. The results show that after one-year planting in the intercropping systems, the maize yields of the wheat/maize/soybean are higher than those of the wheat/maize/sweet potato, however the differences are not significant. After two or three-years strip rotation, the maize yields of the wheat/maize/soybean are considerably higher than those of the wheat/maize/sweet potato. The two years productions are more than those of the previous year with 679.5 kg/hm2 and 839.1 kg/hm2 on average and with the increases of 9.4% and 12.6% in the two study areas, which reflects a more significant productivity in Shehong than that in Yaan. In general, the uptakes and accumulations of nitrogen of maize are insignificant in the two intercropping systems after the strip rotation before the jointing stage of maize; however, they are significantly higher in the wheat/maize/soybean after the jointing stage of maize. The uptakes and accumulations of phosphorus in the wheat/maize/soybean are lower than those in the wheat/maize/sweet potato significantly, while, the uptakes and accumulations of potassium in the wheat/maize/soybean are higher than those in the wheat/maize/sweet potato from the jointing stage to the flowering stage. The contents of soil nutrients in different crop stripz are varied greatly. The residuals of nitrate nitrogen, available nitrogen and available potassium in the soybean strip are higher than those in the sweet potato strip, with increases of 18.4%, 24.1% and 6.0%, however, the residuals of ammonium nitrogen and available phosphorus in the sweet potato strip are higher than those in the soybean strip, with increases of 18.9% and 17.1%. The contents of soil nutrients in the maize strip are insignificant after two and three-years strip rotation, and the differences of soil nutrients in cultivated soil layers become small, which indicates that maize can balance the field nutrients better by the strip rotation.