Nutrient Characteristics And Quality Assessment Of Low-yield Paddy Soils In South China

The low-yield paddy soil in south China has a large potential of increasing crop production because of its various types and large area. The improved knowledge of soil quality assessment involving nutrient characteristics and limiting factors is crucial to designing more effective farming systems and thus improving rice production. Many previous studies evaluated soil quality status using physico-chemical properties, but rarely focused on soil biological properties. Moreover, little information is available for a systematic research of soil quality assessment involving high-, medium-and low-productivity paddy soil at a regional-scale. Therefore, the present study focuses on evaluation of low-yield paddy soils including yellow clayey paddy soil, acid sulfate paddy soil, water-logged paddy soil, albic soil and gleyed paddy soil, and the key soil physical, chemical and biological properties were measured to make the soil quality assessment more comprehensively and accurately, and find out the constraints limiting the rice production. The main results and progress are listed as follows:(1) The paddy fields in south China have following characteristics:soil organic matter (SOM) and total nitrogen (TN) exhibit high levels in soils; the concentrations of alkali-hydrolyzable nitrogen (AN) and available zinc (AZn) are significantly higher than their critical levels, indicating an obvious surplus; a large area of southwest China shows a deficiency of available phosphorus (AP)(<10mg kg-1); Soil pH、available potassium (AK), cation exchange capacity (CEC) and available silicon (ASi) exhibit the similar trends in spatial distributions with high concentrations in the southwest China and low concentrations in the southeast. Paddy fields in southeast China are characterized by severe AK deficiency and low status of pH and CEC.(2) The refined minimum data set (MDS) for soil quality assessment of yellow clayey paddy soil included the following indicators:TN, AK, ASi, microbial biomass carbon (MBC) and arbuscular mycorrhizal fungi (AMF). The whole study area is characterized by sufficient AP, ASi and AZn, but deficiency in AK. Low levels of TN, AK and ASi are considered to be the major constraints limiting the rice production of yellow clayey paddy soil.(3) The refined MDS for soil quality assessment of gleyed paddy soil included the following indicators:TN, AK, MBC, β-glucosidase, total bacteria (TB) and AMF. The whole study area shows a surplus of AN and AP, but deficiency in AK. Low levels of TN, AK and soil microbial activity are considered as the primary constraints limiting the productivity of gleyed paddy soil.(4) The refined MDS for soil quality assessment of acid sulfate paddy soil included the following indicators:MBC, AZn, pH, ASi and TN. The whole study area is sufficient in AP and AZn, but deficiency in AK and ASi. Low levels of pH, ASi and TN are regarded as the important constraints limiting the productivity of acid sulfate paddy soil.(5) The refined MDS for soil quality assessment of albic soil included the following indicators: dehydrogenase, TN, pH, SOM and AMF. The whole study area is characterized by high concentrations of AP, ASi and AZn, but deficiency in AK. Low levels of pH, TN, SOM and ASi are considered to be the major constraints limiting the rice production of albic paddy soil.(6) The refined MDS for soil quality assessment of water-logged paddy soil included the following indicators:TN, TB, AP, phosphatase and AMF. The whole study area is rich in AN, ASi and AZn, but deficiency in AP. Low levels of TN, AP and AK are considered as the major constraints limiting the rice production of water-logged paddy soil.