Spatial And Temporal Variation Of Eco-environment Of Rice Planting Areas In Guangdong Province And Its Comprehensive Evaluation

Rice is the second largest grain crop,and China is the largest producer and consumer of rice in the world.Rice quality is closely related to people's health,and the environment of rice planting area has become the key to the safety and quality of rice.Although rice is the first major food crops in Guangdong province,which is one of the China's largest demand regions of grain for its typical food-deficit,and food security occupies an important position in the country.So,through the methods of literature review,data collection,field investigation,sampling and laboratory analysis,and based on the software of Microsoft Excel 2016,SPSS 21.0 and ArcGIS 10.2,this paper analysed the spatial and temporal variation of eco-environment of rice planting areas in Guangdong province and comprehensive evaluation was performed from the aspects of landform environment,climatic environment,atmospheric environment,water environment,soil environment,biological environment and human environment,respectively,to provide a reference basis for comprehensive understanding the eco-environmental quality of the rice planting areas in Guangdong province.The results showed that:?1?The topography in Guangdong province is complex,and the area of mountain, hilly,plain and terrace occupies the total area of Guangdong is 31.7%,28.5%,23.7%and16.1%,respectively.And most of the areas in Guangdong are suitable for rice planting.The comprehensive evaluation level of terrain environment and the paddy field is higher,and the first-class paddy field area is 182.18×10⁴ hm²,occupies 71.2%of the total paddy field area;the second-class paddy field area is 23.48×10⁴hm²?9.2%?;the third-class paddy field area is 31.58×10⁴ hm²?12.3%?;the fourth-class paddy field area is 14.37×10⁴ hm²?5.6%?;the fifth-class paddy field area is 3.67×10⁴ hm²?1.4%?;the sixth-class paddy field area is 0.60×10⁴hm²?0.3%?.?2?Guangdong province belongs to the East Asia monsoon region and it presents as central subtropical climate,south subtropical and tropical climate from north to south.It is one of the regions of the most abundant of light,heat and water resources in China and simultaneous heat and moisture.Except that the north Guangdong mountainous area is not suitable for double rice planting,the climate in the other 95%area in Guangdong is suitable for double rice planting.?3?The atmospheric environment quality in Guangdong has been improved significantly in recent years and the pH value of precipitation increases year by year while the acid rain frequency decreases.The annual variation range of the six pollution indicators of air quality in Guangdong is small,the average concentration gradually decreases with the years,and the overall target rate reaches 90%.More than 70%of the province's area of the atmospheric environmental quality achieved good level.Atmospheric environmental factors and the comprehensive evaluation level of paddy field is higher,the first-class paddy field area is 118.76×10⁴hm²,occupies 46.4%of the total paddy field area;the second-class paddy field area is 71.73×10⁴hm²?28.0%?;the third-class paddy field area is 65.39×10⁴hm²?25.6%?.?4?Rice irrigation is mainly composed of surface water irrigation in Guangdongprovince,which almost accounting for 95%,and the irrigation water is relatively abundant and can meet the need of rice irrigation.However,the waste water pollution is quite serious,and the total amount of waste water discharge increased by 6.868 billion tons from 1990 to2016.In recent years,the cross section's water quality is?^?class quality remained around 50%,which mainly include the total phosphorus and oxygen organic matter,etc.?5?The pH value of soil in Guangdong province is about 5.48,indicating that the soil in Guangdong is mainly acidic and weakly acidic soil.The soil nutrient quality reaches the medium level in more than 50%region in Guangdong,which can provide good soil condition for rice growth.However,heavy metal pollution is more serious throughout the whole province,especially in the Pearl River Delta region.The comprehensive evaluation grades of soil environmental and paddy field is general.The first-class paddy field area is12.97×10⁴hm²,occupies 5.0%of the total paddy field area;the second-class paddy field area is 32.06×10⁴hm²?12.5%?;the third-class paddy field area is 87.24×10⁴hm²?34.1%?,the fourth-class paddy field area is 80.35×10⁴hm²?31.4%?,and the fifth-class paddy field area is 43.25×10⁴hm²?17.0%?.?6?During the process of rice planting,the diseases and insect pests of rice present a volatility increasing trend and the occurrence degree belongs to moderate and some serious level.The total area of rice diseases and insect pests was 1.59×10⁸hm²·times from 1992 to2016,and the rice insect pests occurrence area is significantly heavier than the disease over the years.Furthermore,the proportion of the insect pests occurrence area increases while the disease reduces year by year.The order of actual loss of unit area from big to small is Xanthomonas oryzae>Pyricularia oryzae>Rhizoctonia solani>Nilaparvata lugens>Scirpophaga incertulas>Cnaphalocrocis medinalis.The Grass,the Mouse and the Screw,the occurrence degree belongs to moderate to serious level.The actual loss caused by the Grass,the Mouse and the Screw is 31.28%?61.41%and 7.71%,respectively.?7?Rice planting in Guangdong province is significantly affected by human activities.Fertilizer application amount per planting area increased from 286.36 kg/hm²in1990 to 540.32 kg/hm²in 2016,which is higher than the warning line of 225 kg/hm²putting forward by the government.The total pesticide application was increased by 30.08%and the dosage per unit area increased by 40.42%.During the 1995-2016,the total amount of agricultural film and mulching film increased by 17,900 t and 14,700 t,and the per-unit area using increased by 4.16 kg/hm²and 3.25 kg/hm²,respectively.From 2010 to 2016,the variation of pollutant emissions from open burning of rice straw was small,among which CO₂ emissions was the highest,while SO₂ emissions was the lowest.?8?From the comprehensive analysis of the terrain-the atmosphere-the soil and the paddy field,we can see that the comprehensive evaluation level is very high.And the paddy field area of optimal is 47.51×10⁴hm²,accounting for 18.8%of the total area of paddy field;the paddy field area of good grade is 98.21×10⁴hm²,accounting for 38.9%;the paddy field area of qualified is 86.55×10⁴hm²,accounting for 34.3%;and the paddy field area of lower grade is 20.37×10⁴hm²,accounting for 8%.