Characteristics And Its Mechanism Of Grain Yield In Typical Cropland Under Long-term Fertilization In China

Crop grain yield is comprehensive performance of factors from soil fertility, climate conditions and management practices and so on. The fertilization application is one of the main management practices to increase crop yields. At present, more and more people pay attention to the problems that degrees and trends of the effects of long-term fertilizer application on sustainability of food production and soil quality. Maize, wheat and rice are main food crops in the world, especially in China. Grain yields of maize, wheat and rice were collected from 20 long-term experiment sites under a wide range of soil types, climatic conditions and crop management practice in China. Most of experiments had eight treatments: non-fertilization (CK), nitrogen fertilization (N), nitrogen-potassium fertilization (NK), nitrogen-phosphorus fertilization (NP), phosphorus-potassium fertilization (PK), nitrogen-phosphorus-potassium fertilization (NPK), manure with NPK fertilization (NPKM) and manure (M) with single or double cropping systems. The main results and conclusions are given as following:(1)Grain yields were significantly higher in the NP, NPK, M and NPKM treatments than those in the CK treatments across all the sites. The highest grain yields were found in the NPK and NPKM treatments. The maize, wheat and rice yields in NPKM treatments were 7140 kg?hm-2, 4230 kg?hm-2 and 5892 kg?hm-2, respectively. Compared to the CK, the grain yields in the NPKM treatments increased by 142%, 229% and 81%, respectively. Wheat grain yields in the NP, NPK and NPKM treatments showed a significantly positive relationship with the latitude, i.e higher wheat yield in the northern China. For the sites in the southern China (Qiyang, Jinxian, Xuzhou and Wuchang), grain yields were significantly higher in the NPK (NPKM) treatments than that in the NP (NPK) treatments, showing increases of 11%～86% and 11%~21% for maize, and wheat/rice, respetively. The grain yield of maize, wheat and rice were decreased under double cropping than single cropping by 49%, 34% and 46%, respectively.(2)The interannual fluctuations in grain yields of wheat and maize were greater than that of rice. The maize and wheat yields in the CK, N, NK and PK treatments showed a significant declining trend. There was an increasing trend for the NPK and NPKM treatments although the trend was not statistically significant. The annual change rates of maize yield were 12 kg?hm-2 and -23 kg?hm-2 under the single and double cropping systems, respectively. Overall, the locations or the climate conditions had little effect on the annual change rates of rice grain yield, but considerable effect on those of maize and wheat yield. The annual change rate of maize and wheat yields showed generally positive relationships with the latitude and annual sums of sunshine hours, but negative relationships with annual mean temperature and effective accumulated temperature. These results indicate that the northern China has potential for continuous increase in maize and wheat yield.(3)The sustainable yield index (SYI) of crop varied with fertilization, crop types, effective accumulated temperature and the sunshine hours. Generally, the SYI of rice was higher than that of both maize and wheat by 0.1~0.2 regardless of fertilization. As a general rule, a good sustainable yield was obtained under NPK, NPKM and M treatments when the SYI value was more than 0.55, while a worse sustainable yield under control, N and NK treatments when the SYI was less than 0.45. The crop SYI was also affected by the longitude, altitude and climate condition, especially for maize, followed by wheat. The variation of SYI for maize, which was affected by effective accumulated temperature and the sunshine hours significantly, is biggest among the three major crops in China. It indicated that the rice yield sustainability was higer than that of maize and wheat. The sustainable of grain yield in NPKM treatment was the highest among all the treatments.(4)On average, the soil basic fertilities of rice (42%~79% across sites, average 62%) were higher than that of wheat (20%~61% across sites, average 36%) and maize ( 10%~79% across sites, average 42%). The significantly positive correlation between the fertilized and unfertilized grain yields. When the yields of unfertilized crops increased one unit, the magnitude of yields increased in NPKM treatments decreased by 0.12-0.31 compared with that in NPK treatments. The grain yields under long-term NPK fertilization were more dependent on soil basic fertility than that of NPKM fertilization.In a word, the decline trends of yields were observed for wheat and maize with no fertilizer or unbalanced fertilizers of chemical applied, especially in the Southern China. It showed that maize and wheat yields in the Northern China were high and stable. However, rice yield was little response to spaces and different fertilizer application across all sites. In order to increase the crop yield, the potassium fertilizer and manure should be applied in Southern China. Chemical fertilizer in combination with manure is more effective way to improve and maintain the grain yield, and it is strongly recommended for sustainable agriculture.