滴灌施肥对甘蔗土壤碳固持与温室气体排放的影响及其机理

Irrigation and fertilization not only affect crop yield and quality, but also play important roles in soil organiccarbon sequestration and greenhouse gas emission. Drip fertigation, as an efficient technique of irrigation and fertilization management, is widely applied in Guangxi and other regions of China. However, very limited information is available in terms of the effects of drip fertigation on soil organic carbon sequestration and greenhouse gas emission. In this project, we will investigate the effects of drip fertigation on soil carbon sequestration and greenhouse gas emissions in sugarcane field of Guangxi, where the planting area of sugarcane accounts for more than 60% of the national total.Firstly, we will investigate the effect of drip fertigationon soil organic carbon pool dynamics and unravel the underlying mechanism in combination with soil organic carbon fraction and microbial indices, including soil microbial biomass carbon and nitrogen, soil microbial community structure and enzyme activities.We will also measure soil CO2, CH4 and N2O fluxes.The underlying mechanism of drip fertigation on greenhouse gas emission will be assessed. The net global warming potential will be determined by considering both soil organic carbon storage and the fluxes of greenhouse gases.In addition, we willestimate the water and nutrient use efficiency under different water and fertilizer management. The results of the study will contribute to understand the carbon sequestration and greenhouse gas emissionafter implementation of drip fertigationin sugarcane fieldof Guangxi, and provide scientific support for irrigation and fertilization management of sugarcane in Guangxi or China.

水肥管理不仅影响作物产量与品质，也对土壤有机碳固持与温室气体排放具有重要作用。滴灌施肥作为一种高效的水肥管理技术正被广西及全国其它地区重点推广，然而目前对其固碳效应与温室气体排放的认识还很不足。项目以广西典型区域的甘蔗地为研究对象，采用野外控制实验结合室内分析等手段，首先研究滴灌施肥对土壤有机碳库的影响，结合不同稳定性有机碳组分与微生物指标，探讨滴灌施肥对土壤有机碳库的影响机制，同时将研究滴灌施肥对土壤CO2、CH4和N2O通量的影响，并结合土壤生物与非生物因子分析滴灌施肥影响温室气体排放的机理。在此基础上，综合土壤有机碳储量与温室气体排放通量评估滴灌施肥对甘蔗土壤净增温效应的影响，以及估算不同水肥管理下水分与养分利用效率。研究结果将有助于深入理解广西甘蔗实施滴灌施肥的固碳效应与温室气体排放，为广西或中国甘蔗水肥管理提供科技支撑。

滴灌施肥对甘蔗增产具有一定的积极意义，合理的滴灌施肥模式有利于甘蔗高产和温室气体减排，本研究滴灌施肥对甘蔗土壤碳固持与温室气体排放的影响及其机理，结果得出：（1）在滴灌条件下，W300F120处理（灌水量：180 m3·hm-2；施肥量：商品有机肥15000 kg hm-2、N 300 kg hm-2、P2O5 180 kg hm-2、K2O 240 kg hm-2）甘蔗产量（124 t hm-2）和产糖量（19.66 t hm-2）最高；W2DF120处理（土壤水分：苗期和成熟期为70%~80% θf （田间持水量），分蘖期和伸长期为80%~90% θf；施肥量：商品有机肥15000 kg hm-2、牛粪7500 kg hm-2、N 300 kg hm-2、P2O5 180 kg hm-2、K2O 240 kg hm-2），F55（氮肥基追比5:5）下W1（70% ~ 80%θf）和W2（80% ~ 90%θf）处理、F12（N 300 kg·hm-2、P2O5 180 kg·hm-2、K2O 240 kg·hm-2）下W75（45 mm）和W100（60 mm）处理均是提高甘蔗产量和产糖量的较优滴灌水肥供应模式。（2）土壤总有机碳（TOC）、可溶性有机碳（DOC）、微生物量碳（MBC）、易氧化有机碳（ROC）以及转化酶、过氧化氢酶、纤维素酶和淀粉酶活性均在分蘖期相对较高；W300F120处理土壤DOC含量和土壤转化酶、淀粉酶和纤维素酶活性较高，W2DF120处理土壤MBC和纤维素酶活性较其他处理高，而土壤CH4和CO2排放通量均较低；蔗田土壤CH4排放通量与土壤DOC，土壤TOC与转化酶活性，土壤ROC与纤维素酶和转化酶活性，土壤MBC与转化酶、纤维素酶和过氧化氢酶活性；蔗地N2O排放通量与土壤氨基酸态氮含量、亚硝酸还原酶、脲酶活性、嗜酸单胞菌和亚硝化螺菌属丰度均呈显著正相关关系；蔗田N2O通量与土壤铵态氮含量、脲酶和硝酸还原酶活性以及中慢生根瘤菌属丰度之间均呈显著负相关。（3）灌溉和施肥显著影响土壤微生物群落结构组成和丰度，水肥一体化蔗田土壤中反硝化细菌（放线菌纲和变形菌纲为主）在土壤氮素转化以及N2O排放等方面发挥重要作用。