| Straw returning, considered to a necessary method of maintain the soil sustainable productivity, is a common fertilizer-applying measure, which has a long history in China. Being charred from biomass by pyrolysis under complete or incomplete absence of oxygen condition, biochar is a highly aromatic and low density carbonized solid matter with infusibility. It has been shown that biochar has effects of carbon sequestration, increasing soil organic matter, promoting the crop yield. High temperature and rainy climate of Hainan formed the high acidity and poor fertilizer retention ability of soil, which also determines the low utilization ratio of nitrogen. Straw and biochar has a huge potential of amending the soil acidity and enhancing soil fertility ability,and may affect the utilization of nitrogen. N2O is an important greenhouse gas. Changes of soil properties affect the formation and emission of N2O. The changes of soil properties caused by the addition of straw and biochar can affect the N2O emission, however studies about effects of straw and biochar on N2O emissions from papaya plantation soils have not been reported. Papaya is an important cash crops in the tropics. It needs to applied plenty of nitrogen fertilizer and water during the growth period. The experiment chooses papaya plantation soils as study object. The effects of straw and biochar on soil properties, soil N2O emission from papaya plantation and papaya agronomic were studied in this paper with field experiment and incubation experiments. There were 6 treatments in field experiment:urea+20 t/ha of biochar (C1), urea+40 t/hm2 of biochar (C2), urea+20 t/hm2 of biochar+20.12 t/hm2 of straw (CS), urea+40.23 t/hm2 of straw (S), single urea (CK) and no urea (NO). Four treatments in incubation experiment including no organic material addition (CK),1% biochar addition (1%C),2% biochar addition(2%C) and 2.75% straw addition (2.75%S). The main research results are as follows:1?The comparative experiments indicate that the application of straw and biochar could promote improve the physical and chemical characters and fertility of soil. Incubation experiment showed that straw and biochar amendment significantly increased organic carbon, available phosphorus, available potassium, soil total nitrogen concentration, soil pH and CEC. The effect of biochar was better than that of straw, and the improvement effects increased with biochar dosage. Field experiment showed that straw and biochar amendment significantly increased soil pH and CEC, increased organic carbon, available phosphorus, soil total nitrogen concentration, decreased soil bulk density.2?In incubation experiment, biochar promoted biochar nitrification, shortened nitrification time, reduced soil ammonium nitrogen, accelerated nitrate accumulation, and with biochar application dosage was positively correlated. Early in the straw into the soil can significantly reduced the amount of soil mineral nitrogen, the latter can contribute nitrification to carry out. In field trials, straw and biochar can promoted nitrification, reduced soil ammonium nitrogen content in not significantly degree, straw and biochar soil nitrate accumulation was not observed in straw and biochar soil, it may have occurred nitrate leaching or absorbable by crops.3?In incubation experiments, biochar could stimulate soil produced N2O emissions peak at the beginning of the cultured stage. Biochar reduced emissions of N2O in late culture period significantly, the N2O cumulative emissions of 1%C and 2%C decreased by 55.18% and 43.08% respectively, compared to CK. Straw significant decreased 86.19% N2O emissions during the initial stage of the experiment, and significant increased by 150.21% N2O emissions in the late experiment. Field experiment showed that biochar could reduce N2O emissions, straw promoted N2O emissions. The N2O cumulative emissions of C1?C2 and CS was 6.91 kg N2O-N/hm2,6.47 kg N2O-N/hm2 and 6.12 kgN2O-N/hm2, compared with CK decreased 23.15%,29.21% and 33.55% respectively, the difference was not significant. The N2O cumulative emissions of S was 10.66 kgN2O-N/hm, higher than other treatments, and increased by 15.61% compared to CK.4?There was no correlation neither between N2O emissions and WFPS of 5 cm soil or temperature of 5 cm soil. A significant positive correlation was found between N2O emissions and amounts of fertilization or pH.5?The results showed that straw and biochar application increased plant height, stem circumference, leaf number and crop yields. The papaya yields of C1?C2 and CS compared with CK increased 21.25%,16.58% and 30.55% respectively, and significant difference was observed between S and CK.The application of biochar can improve soil fertility as well as soil properties, reduce emissions of N2O and increase yield of papaya, provide economic and environmental benefits and marketing spread potential in tropical soils. |
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