Discussions On Carbon Cost Of Agricultural Production And Application Of Biochar-Based Compound Fertilizers

Reducing greenhouse gas emission to alleviate global warming has become hotspot of the international community recently. To clear the trend of greenhouse gas emission, clear the ways of emission reduction and develop the corresponding emission reduction technology of agricultural production, I have done research on the following aspects. First, we evaluated the carbon footprint of greenhouse vegetable production based on questionnaire survey in Nanjing and seeked for the key factor that impacted agricultural carbon footprint; then we studied the effect of biochar-based compound fertilizers on rice according to the survey results to develop the key mitigation technologies, the main results are as follows:(1) A questionnaire survey of material and management inputs in production of five typical kinds of greenhouse vegetables from Nanjing was conducted. Carbon cost and C emission intensity involved in these vegetable productions were evaluated using life cycle analysis methodology. Results showed that the total C inputs in a single growing season of the studied5types of greenhouse vegetables ranged from867.1±240.6kgCE·ha-1to2039.4±163.3kgCE·ha-1. While the material input possessed a poredominant proportion in the total C cost, fertilizers and agricultural films were found in a proportion of58%-82%and of12%-29%, respectively. Furthermore, there were significant differences in the C intensity either per hectare or per ton of production between the vegetable types. Above all, reducing C input in the growing of vegetables and better application techniques to improve nutrient uptake and choosing suitable greenhouse vegetable varieties would be an effective measure to increasing carbon sequestration and emission mitigation in soil.(2) Rice shoot dry weight of HWF treatment was significantly higher than that of BBF treatment or had a higher trend at tillering and jointing stage, which provided a basis for crop nutrient uptake and yield increase. Biochar-based fertilizer treatments had great influence on rice root/shoot ratio during the growth period before or at jointing stage while had no obvious effect after the stage. The rice root/shoot ratio of biochar-based fertilizer was higher than that of BBF treatment in early stage of rice when there was no significantly difference between different treatments in the medium and latter stages.(3) With the N application rate reduced by20%than CF treatment, the BCF treatments increase rice economic yield by more than9%,when the BCF of wheat straw has the best efficiency of yield increased up to23%. Among all the yield component factors, the factor of single panicle weight and grain number per panicle made the greatest contribution. Rice plants of BCF treatments could still maintain or even more than the production level of conventional chemical fertilization when the N application rate reduced by20%than CF treatment. The results showed that BCF application could reduce nitrogen fertilizer application amount.(4) At the same time, the BCF treatments promoted the distribution of nitrogen to grain, increasing mass ratio of grain nitrogen and stem and leaf nitrogen by30%-69%, BCF treatments increased nitrogen partial factor productivity (NPFP) by74%-33%, nitrogen harvest index(NHI) and nitrogen grain production efficiency(NGPE) of rice also improved significantly.Rice grain phosphorus accumulation、stem-and-leaf phosphorus accumulation and plant phosphorus accumulation of HWF treatment was significantly higher than those of BBF treatment; Rice grain potassium accumulation、stem-and-leaf potassium accumulation and plant potassium accumulation of WSF treatment was significantly higher than those of BBF treatment and MSF treatment. The results showed that the BCFs could promote rice N, P, K nutrient absorption and improve nitrogen utilization.(5) The ammonium nitrogen content of BBF treatment was lower than that of BCF treatments after jointing stage though top dressed more nitrogen fertilizer at tillering stage compared with the BCF treatments. The nitrate nitrogen content of BBF treatment was significantly higher than that of HWF and WSF treatments in10～20cm soil layer at jointing stage, significantly higher than that of MSF、PHF and HWF treatments in10～20cm soil layer at heading stage, significantly higher than that of HWF treatment in10～20cm soil layer at mature stage, significantly higher than that of WSF、MSF、PHF and HWF treatments in40～60cm soil layer at mature stage,but there were no significant difference between BBF treatment and bochar-based compound fertilizer treatments in other soil layers at other growing times. The experiment demonstrated that the BCFs could reduce the nitrate-nitrogen leaching risk, meet the demand of rice growth for ammonium nitrogen nutrient in the medium and latter stages and improve soil nitrogen supply ability so paddy soil could achieve stable nitrogen supply.