传统稻鱼系统生产力提升对稻田水体环境的影响

如何在提升传统农业系统生产力的同时又不破坏其内涵、还对环境不产生负面影响,是一个受到研究者持续性关注的挑战性课题。本研究以具有1 200年历史的全球重要农业文化遗产稻鱼系统为例,研究稻鱼系统鱼的放养密度对生产力和环境的影响,探讨能够显著提升稻鱼系统生产力且又不破坏其传统性(产品优质、环境友好)的途径。研究表明,传统稻鱼系统(RF)(田鱼目标产量375 kg.hm 2)与水稻单作系统(RM)水体的化学需氧量(COD)、总氮(TN)、总磷(TP)及铵态氮(NH4+-N)含量均没有显著性差异。随着田鱼养殖密度提高(鱼产量由750 kg.hm 2提高到3 000 kg.hm 2)和饲料投入的相应增加,稻鱼系统的生产力和经济产出大幅度提高(稻鱼系统的净经济收入增加25.2%~101.4%),但稻鱼系统(RF)水体的COD值及TN、TP和NH4+-N含量均呈现增加的趋势,尤其是当鱼目标产量增至3 000 kg.hm 2时,水体TP含量和COD值显著提高,面源污染风险增加。分析还表明,鱼放养目标产量为2 250 kg.hm 2时,稻鱼系统经济效益最佳,此时净经济收入比传统稻鱼系统增加55.9%,并且不会对水体环境质量产生负面影响。

Effects of improved traditional rice-fish system productivity on field water environment

World agriculture currently faces great challenges in producing sufficient food while minimizing negative environmental effects of crop cultivation, requiring us to rethink current agricultural production processes. Traditional agricultural systems based on local species diversity and interactions have contributed to food and livelihood security throughout the world for centuries. As human population increased, however, traditional agricultural systems faced daunting challenges in food demand and supply due to the lower economic benefits of the systems. Thus improving the productivity of traditional agricultural systems in a sustainable way has been of great concerned to producers and decision-makers. To determine the feasibility of increasing traditional agricultural productivity without corresponding increase in negative environment impacts, two experiments were conducted at a traditional rice-fish co-culture site that had been operated for over 1 200 years in southern Zhejiang Province. In the first experiment, three treatments without pesticide, including rice monoculture (RM), rice-fish co-culture (RF) and fish monoculture (FM), were compared. In addition to measured rice yield (in RM and RF), fish yield (in RF and FM), and surveyed input-output economics, focus was put on total nitrogen (TN), total phosphorus (TP), total ammonia nitrogen (NH₄⁺-N) and chemical oxygen demand (COD) in field water. Four fish density treatments, including with target fish yields in rice-fish co-culture fields of 750 kg·hm^-2 (RF750), 1 500 kg·hm^-2 (RF1500), 2 250 kg·hm^-2 (RF2250) and 3 000 kg·hm^-2 (RF3000), were designed in the second experiment. Rice and fish yields, input and output of economics, and TN, TP, NH₄⁺-N and COD were measured in the field water. The first experiment showed no significant difference in rice yield between RM and RF. There was also no significant difference in fish yield between RF and FM in the experiment. However, total and net income of the system were higher in RF than in RM and FM. Field water contents of TN, TP, NH4+-N and COD were not significantly different between RF and RM. The second experiment showed that rice yield, fish yield, and total and net economic output increased with increasing fish stock density and fish feed input. Increase in fish stock density increased target yield of fish by 1 500 kg·hm^-2 (50%), significantly increased net income of rice-fish co-culture systems by 25.2%~101.4%, and also increased COD, TN, TP and NH₄⁺-N content in field water. When target yield was 3 000 kg·hm ^-2, TP and COD contents became significantly higher than in other treatments; which enhanced risk of environmental pollution. Economic analysis indicated that target fish yield of 2 250 kg·hm^-2 gave higher economic income and with little impact on field water environment.