Effects Of Organic Fertilizers On The Root Growth And Nutrient Absorption Of Rice And Emission Of Greenhouse Gases From Paddy Field

Rice is one of the most important food crops. Organic fertilizers play an important role in crop production in China. However, little is known about the interaction between nitrogen (N) fertilizer management and organic fertilizers on root growth and nutrient absorption of rice, soil properties and emission of greenhouse gases from paddy fields. In this study, japonica rice cultivar Yangjing4038and Yangfujing8were used and four kinds of organic fertilizers including maize straw (MS), compost made from maize straw (MC), maize residue of methane-generating (MR), and black carbon made by maize straw (BC) were applied to the paddy field before rice transplanting, with no organic fertilizer application as control (CK). Effects of each organic fertilizer on grain yield, root growth, nutrient absorption of rice, soil properties and emissions of greenhouse gases from paddy fields were investigated under both no N application (ON) and site-specific N management (SSNM). The main results are as follows:1. Grain yield ranged from5.9t ha-1to10.8t ha-1under different treatments. At the ON level and when compared with the control (CK, no organic fertilizer application), grain yield was increased by32.2%,13.6%and25.4%, respectively, for MS, MC and MR in2011, and by32.2%,33.9%and35.6%, respectively, in2012, and the differences were significant. Under the SSNM, grain yield was increased by9.5%,4.8%,10.7%and-1.2%in2011, and by9.9%,18.7%,13.2%and16.5%in2012, respectively, for MS, MC, MR and BC when compared with respective ON treatments.2. Compared with respective CK, application of organis fertilizers increased root dry weight, root length, root diameter, total absorbing surface area and active absorbing surface area of roots, root oxidation activity, amount of root bleeding sap, and contents of hormones in roots, zeatin (Z)+zeatin riboside, indole-3-acetic acid (IAA), gibberellins (GA1+GA4), and abscisic acid (ABA). SSNM increased root growth, such as increase in root dry weight, root length, amount of root bleeding sap, and Z+ZR and IAA contens in roots, relative to the ON treatment. At the ON level, the increase in root growth was the most for MR and the least for BC. When N was applied, the increase in root growth was the most for MC and the least for MS.3. Application of organic fertilizers increased contents of organic matter, available nutrients in soil and enhanced soil respiration. The MS treatment reduced soil bulk density under either ON or SSNM. The soil bulk density was decreased under the ON, whereas it was increased under SSNM, for MR, MC, and BC treatments.4. The emission of methane (CH4), carbon dioxide (CO2), or nitrous oxide (N2O) from the field exhibited a similar trend during the whole rice growing season under all the organic fertilizer treatments. Application of organic fertilizers significantly increased the emission of each greenhouse gas and global warming potential (GWP) except the N2O emission which was not increased under the BC treatment, relative to that under CK. Under the same organic fertilizer treatment, SSNM increased emissions of all the greenhouse gases and GWP, whereas decreased GWP per unit grain yield (amount of GWP/grain yield), when compared with ON.The results indicate that application of organic fertilizers, such as MS, MC, and MR, could increase grain yield and improve physical and chemical properties in the soil, but also enhance emissions of greenhouse gases from the paddy field. Both higher grain yield and higher environmental efficiency would be achieved by the adoption of SSNM and the application of MR or MC fertilizer.