Differences of dry matter accumulation and distribution of maize and their responses to nitrogen fertilization in maize/soybean and maize/sweet potato relay intercropping systems

【Objectives】The southwest region is the third major maize producing area in China where the maize yield is 750 kg/ha lower than the national average yield. Due to exceptional weather conditions in this region, intercropping is the main planting pattern of maize. How to use intercropping advantages and previous crop stubble features is a new approach to increase maize yield in this region. In order to explore a new way to improve maize yield and a reasonable nitrogen management to keep a sustainable yield increase of intercropped maize, a field experiment was conducted to investigate dry matter accumulation, distribution, transportation and their responses to nitrogen fertilization under maize/soybean(MS) and maize/sweet potato(MSP) relay strip intercropping systems from 2008 to 2011 in two major maize producing areas in Sichuan.【Methods】 A single factor experiment including maize/soybean and maize/sweet potato relay strip intercropping systems was developed to explore effects of different planting patterns on maize dry matter accumulation, distribution and transportation in 2008.From 2009 to 2010, the experiment was set up by strip rotation, which made the two intercropped crops strips be exchanged, including growing maize on the strips of land which were soybean (or sweet potato) strips the previous year, so did soybean (or sweet potato) to explore effects of intercropping and crop rotation on maize dry matter accumulation. In 2011, effects of different nitrogen application rates (N0, N90, N180, N270 and N360) on maize dry matter accumulation and distribution and their responses to nitrogen fertilization were studied using the micro-plot experiment.【Results】 1) From the dough stage, the dry matter accumulation of maize and dry matter transportation efficiency in stem-sheath in the maize/soybean intercropping system are significantly higher than those in the maize/sweet potato intercropping system with a yield increasing of 2.4%-3.2%, however, the yield difference is insignificant. 2) After the strip rotation, as a result of the rotation effect and intercropping advantages, the maize dry matter accumulation in maize/soybean is significantly higher than that in maize/sweet potato from the jointing stage, and the difference reaches to 26.8 g/plant at the maturing stage. The transportation efficiency and contribution rate in stem-sheath and the harvest index in the maize-soybean intercropping system are also significantly higher than those in the maize-sweet potato intercropping system, with the harvest index increased by 3.9%. Eventually, there are bigger increases of maize yield in maize-soybean intercropping with increases of 7.4% and 14.4% according to the 2-yr field experiments of the two experimental sites. 3) The maize dry matter accumulation and distribution and yield responding to the nitrogen fertilization are significantly different between the maize/soybean and maize/sweet potato intercropping systems. Application of nitrogen fertilizer of 180 kg/ha in the maize-soybean intercropping and of 270 kg/ha in the maize-sweet potato intercropping could help to increase the accumulation of photosynthate and dry matter increasing rate and also extend the length of the continuous filling days. And at the same time, the dry matter transportation from stem-sheath and leaf to grain and the harvest index are increased significantly and then the potential for increasing maize yield is improved. The maize/soybean intercropping increases maize yield significantly under low nitrogen treatment (0-180 kg/ha), however, yield difference is insignificant between the two intercropping systems under the high nitrogen treatments.【Conclusions】 Optimization of planting patterns is one of the way to increase the yield of maize in the southwest, and maize intercropped with soybean and growing with crop rotation can increase maize yield and avoid continuous cropping barrier. Nitrogen management is different with different cropping systems, the nitrogen fertilizer of 180 kg/ha has an obvious effect of increasing maize yield in the maize/soybean relay strip intercropping system in moderate-fertility and high-fertility soil. However, the nitrogen application rate should be raised to 270 kg/ha when maize intercropped with sweet potato.