Effect Of Soil Surface Mulching On Carbon Fractions On Dryland

Rational mulching of soil surface becomes more and more important to elevate crop yields and maintain soil productivity. Plastic and sraw mulching has been found to be able to change soil water content, fertility, and gas and heat situations, and then affects soil organic carbon mineralization and immobilization. A long-term field experiments were carried out to take soil samples at main seasons of winter wheat to study the effect of soil surface mulching on carbon fractions in dryland soils. The crops were planted at 0, 120 and 240kg N /ha on the basal application of 100 kg P2O5 /ha, and under three cultivation patterns including the conventional no-mulching (CNM, no soil surface mulching and no supplemental irrigation), the plastic mulching (PM, mulching soil surface with plastic film over the entire growing season), the crop straw mulching (SM, mulching soil surface with crop straw over the entire growing season). Determination was performed on soil total carbon (TC), soil organic carbon (SOC), soil inorganic carbon (SIC), and light fraction organic carbon (LFOC) in different winter wheat growth season, soil surface mulching and N rates. The main purpose of this study was to heighten the immobilization capacity of organic carbon, maintain soil fertility and optimize cultivation patterns in dryland soil. The main conclusions are as follows:1. The PM treatment was found to enhanced the accumulation of TC and IC and decreased the accumulation of TOC and LFOC at 0-40cm soil layers by 0.6-5.2Mg C /ha and 104.2-221.9 Kg C /ha respectively compared to CNM treatment. SM treatment elevated SOC by1.0-5.5 Mg C /ha from pre-seeding to reviving and LFOC by 272.4-750.1 Kg C /ha in all winter wheat growth seasons, while the accumulation of SIC decreased at 0-40cm soil layers in all seasons. Seasonal changes of SIC are different with soil surface mulching. SIC decreased significantly at reviving and flowering stage under CNM and SM and have no change before at flowering stage under PM and decreased significantly at harvesting stage for all treatments at 0-40 soil layers. For all treatments, TC and SOC increased significantly at reviving or flowering stage, but decreased significantly at harvesting. LFOC decreased gradually from sowing to reviving stage and then increased gradually to harvesting. LFOC tended to be stable at wintering stage of low temperature, while fresh organic material were decomposed to light fraction organic matter with temperature increasing in the spring.2. The treatment of N application at 120kg/ha decreased accumulation of TC and IC at 0-40cm soil layers under CNM treatment, while increased N fertilizer rate don't affect them. N application increased obviously SOC accumulation. When applying N at 120 and 240 kg/ha, SOC increased by 2.0 and 2.1 Mg C /ha respectively compared to no N fertilizer under CNM treatment. Accumulation of LFOC was not affected by N rates at 0-40cm soil layers under CNM treatment. In the case of PM, TC and IC increased with applying N at 0-40cm soil layers, while SOC and LFOC decreased with the increase of N rates. When applying N 240 kg/ha, SOC and LFOC decreased by 5.3 Mg C /ha and 444.6 kg C /ha respectively compared to no N fertilizer application at 0-40cm soil layers. After N applied, the increase of TC attributed to IC enhancement, and the decrease of LFOC may be one of reasons, which resulted in the loss of SOC.3. When N supply was deficiency under SM treatment, accumulation of TC and IC increased by 2.2 and 2.8 Mg C /ha with applying N 120kg/ha and accumulation of TC decreased by 3.3 Mg C /ha with applying N 240kg/ha at 0-40cm soil layers compared to CNM treatment. When application of N, SOC had the increase trend under CNM treatment and decreased with the increase of N rates under SM treatment. SOC decreased by 2.8 Mg C /ha with applying N 240kg/ha compared to CNM. Whether applying N or not, mulching soil surface with straw increased LFOC mass in 0-10cm layers, meantime, also increased the accumulation of LFOC in 0-40cm soil layers. Therefore, the higher N application increased the above ground biomass and more residue material could enter into soil to enhance the mass of LFOC. Furthermore, crops need more nutrients to meet growth and result in SOC depletion and TC decrease.4. No matter what is the cultivation patterns and N rates, TC and IC had increase trend at each of 0-40cm soil layers and LFOC increased at 0-10cm layers, but decreased at each of 10-40cm layers at the fallowing stage. However, soil surface mulching and fertilizer N rates influenced the mass of SOC. In the case of CNM with applied N of 0, 120 and 240 kg/ha, the mass of SOC increased correspondingly by 1.6, 2.1 and 1.5 Mg C /ha at 0-40cm soil layers. Under PM and SM with applied N 240 kg/ha treatment, it increased by 3.1 and 1.1 Mg C /ha respectively.