Spatial and Temporal Variability of Soil Organic Matters in Se-rich Areas of Hainan Island in Recent 30 Years

[Objectives] The aim was to reveal the distribution of soil organic matter content in cultivated land in the Se-rich areas of Hainan in 1980and 2010, so as to provide reference for the study on the evolution of soil organic matter content.[Methods] With the combination of field investigation with indoor analysis, the characteristics of organic matter content in the Se-rich areas of Hainan in 1980 and 2010 was revealed by means of spatial analysis, and the differences were analyzed.[Results] In the last 30 years, the proportion of 20-30 g/kg of soil organic matter content in the Se-rich areas of Hainan was reduced, but the content of soil organic matter in the area generally increased. The average value of the content of organic matter in the area was increased from 25.3 g/kg in the 1980s to 28.1 g/kg, but its spatial distribution was uneven.[Conclusions] The farmers should be guided to change the fertilization structure, and attention should be paid to the application of organic fertilizer, so as to improve the soil organic matter content.

Hainan; Nandu River; Soil nutrient; Spatial distribution

[Objectives] Within a research area on basin scale, soil nutrient distribution characteristics and main causes were analyzed, to provide a basis for soil nutrient management on basin scale.[Methods] With the Nandu River Basin of Hainan Island as the research area, by means of geostatistics and spatial analysis methods, the distribution available of soil pH, organic matter, alkali-hydrolyzale nitrogen, available phosphorus, available potassium and available trace elements were studied.[Results] The cultivated land in the Nandu River Basin of Hainan Province is overall acidic, with an average pH of 5.2. The soil organic matter content is overall lower, and its spatial differences are also significant. Soil alkali-hydrolyzable nitrogen, exchangeable calcium and exchangeable magnesium content are at a medium level, but the soil lacks available phosphorus and available potassium.[Conclusions] The differences in pH within the research area might be related to parent materials distribution and fertilizer applications. The main reasons for the low soil organic matter content are inadequate and uneven input of organic fertilizer and high-temperate rainy climate. The lack of soil phosphorus and potassium is mainly caused by unreasonable fertilizer application and climatic and terrain factors.

Distribution of Soil Nutrients in Se-rich Areas of Hainan Island

[Objectives] The aim was to reveal the distribution of soil nutrients in Se-rich area of Hainan and to clarify their specific contents, so as to provide references for the development of Se-rich area agriculture in Hainan.[Methods] With the se-rich area in Hainan as the object, field investigation and indoor analysis were combined to elucidate the nutrient status of cultivated soil in the area and analyze its nutrient distribution.[Results] The soil in the se-rich area in Hainan province was generally acidic with the average soil pH value of 5.0. The difference in soil pH between different landforms and different altitudes was not significant, ranging from 4.9 to 5.3. Soil available P and available K contents were low to intermediate, and the soil available N content was moderate. The farming system, chemical fertilizer application structure and meteorological factors were the main causes of the distribution of soil nutrient elements. The soil exchangeable calcium and magnesium content was rich, and the distribution of trace elements in the arable soil of different terrains and elevations was closely related to the distribution of soil parent material in the region. The increase of soil organic matter content in arable land could be achieved by increasing the application of organic fertilizer and guiding the farmers to enhance the application of straws to fields.[Conclusions] The application of soil N, P and K fertilizers should be combined with the application of soil organic fertilizers to improve the soil fertility of cultivated land.