Influence of altitude correction of potential productivity of crops on agricultural land physical quality grade in Yunnan province

Abstract: Crop potential productivity (PP) refers to the highest yield of fine crop variety per unit area that might be obtained assuming all or part of the factors are in the optimum state. Thermal potential production (TPP) refers to the highest yield of ideal crop colony in the condition of local sunlight and temperature assuming that the agricultural production condition has been fully guaranteed in adequate supply of water, CO2 and suitable states of other environmental factors, while climatic potential production (CPP) refers to the theoretical yield of crops taking precipitation effect into further consideration based on TPP. The "Regulation for Gradation on Agriculture Land Quality" GB/T 28407-2012 (Regulation) provides the crops' TPP and CPP nationwide according to the reports of sowing/harvest date from all provinces, and the meteorological data of 2231 stations from the National Meteorological Administration within 30 years (1961-1990). Each county just provides one set of TPP and CPP data for appointment crop according to the meteorological data from only one station in the county, and the PP value of crop only represents the local conditions. Yunnan Province is the most prominent and representative region of stereo climate in China. There are 1669 dams with the area of larger than 1 km2 across Yunnan Province, totally covering the area of 245.35 hm2. Each county has many combined configurations of "dam-hill-mountain" with larger differences in TPP and CPP. In the first-round grading work on agricultural land quality in Yunnan Province, most of the counties use the TPP and CPP from meteorological stations representing the value of TPP and CPP of the whole county to calculate the agricultural land quality grade index, which must be very different from the actual situations. Therefore, it is particularly necessary to make altitude correction of TPP and CPP in order to ensure the objectivity and veracity of classification results in Yunnan Province. This paper is aimed to obtain the PP value of appointment crops outside the regions with meteorological stations by making altitude correction on TPP and CPP of appointment crops from county meteorological stations in plateau basin regions of Yunnan according to the "Regulation", and to investigate its influence on agricultural land physical quality grade. This paper made an altitude correction model on the TPP and CPP of one-season rice, summer maize and winter wheat according to the TPP and CPP data of appointment crops from 56 county meteorological stations in plateau basin regions where Luliang County locates. Then a paddy land and a dry land of high quality were respectively chosen in each village to verify the rationality of the model according to per unit area yield of actual crops in paddy land and dry land. The differences of agricultural land physical quality grade before and after altitude correction of TPP and CPP in Luliang County were testified. The results showed that the actual crop yield per unit area for one-season rice, summer maize and winter wheat was all less than the value of TPP and CPP before and after altitude correction, and had the same change tendency of the TPP and CPP after altitude correction with the altitude change, and the TPP and CPP after altitude correction of one-season rice, summer maize and winter wheat much more conformed to actual situations than that before. The reduction range of agricultural land physical quality grade after altitude correction was between ?0.8,1.7, 99.76% of which was within 1.5 in Luliang. There is only one meteorological station in each county actually, and most are located in dams, while just few in mountains. The PP could not be calculated based on the meteorological data because lacking the meteorological stations for regions around. Most counties obtained the crops' PP value by using altitude correction in the regions outside meteorological stations in Yunnan. The TPP and CPP after altitude correction were chosen to evaluate the agricultural land physical quality grade if the altitude of the majority of agricultural land in the county was higher than that of the meteorological station, which was a little lower than that before. The regulation model of crop PP changing with altitude is the key to altitude correction, which is directly influenced by choosing standard spot. It is different to build up an altitude correction model for whole province conforming to the actual situation by taking the crops' PP of county meteorological stations as standard spot for certain appointment crops, because the meteorological stations have limited amount and uneven distribution in Yunnan Province. The further research direction is to build up altitude correction model and program in partitions, and to perform the connections in partitions.