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Can biochar mitigate nitrogen losses in organic farming systems?

机译：生物炭可以减轻有机耕作系统中的氮损失吗？

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摘要

Nitrogen (N) management represents a challenge for organic farming systems. In particular, sufficient N mineralization is not always achieved, timing of N release and plant uptake is often not synchronized, and subsequent N transformations of mineralized N may be lost as environmental pollutants (e.g., leached N and nitrous oxide (N2O) emissions). Biochar, the charcoal obtained from the thermal decomposition of biomass waste under limited oxygen supply, has the potential to alter soil physicochemical properties that regulate the retention of soil N. This dissertation evaluates biochar as a means to improve N management in organic farming systems by reducing environmental N losses and stabilizing N within the agricultural landscape. The following three experiments investigated these conditions using a multi-scale approach, including an on-farm trial and greenhouse experiments, high-frequency assessment of greenhouse gases (GHGs), 15N pool dilution techniques, and microbial analysis.;The first experiment examined the effects of a variety of biochar amendments on plant performance, soil properties and N transformation rates in a mesocosm representing an organic lettuce production system (Lactuca sativa ). N2O fluxes were monitored throughout the growing period as well as functional genes that encode nitrification (amoA) and denitrification (nirK, nirS, and nosZ) enzymes of bacteria. Findings from this study indicate that some biochars may accelerate N mineralization from organic fertilizer and increase net nitrification. Decreases in N2O fluxes were only observed for a short period, not leading to significant effects in total emissions. The second experiment examined whether biochar amendments reduce N losses from soils and improve plant performance and whether these effects are N level dependent. Fertilizer inputs, N output through harvest, leachate, and N2O emissions were used to assess N utilization and environmental losses of biochar-amended soils. These evaluations were carried out for two growing seasons in a mesocosm representing an organic lettuce production system. Analyses of plant performance indicate that biochar amendments did not provide any increases in plant biomass in soils that received less than commercial fertilization rates (225 kg N ha -1). At commercial fertilization rates, biochar increased N use efficiency (NUE) and decreased N losses via leaching, which lead to a significant decrease in ratio of N lost over N exported in biomass. N2O emissions were altered by biochar amendments only in soils that received 50% of commercial fertilization rates (112 kg N ha-1), which did not alter the ratio of N lost over N exported in biomass.;The third experiment provides an on-farm high frequency assessment of GHG emissions from biochar amended-soils in an organic walnut orchard, in addition to an estimate of the GHG savings from the conversion of orchard residue into utility grade energy. Despite observed short-term decreases, biochar alone or in combination with compost did not alter total CO2 and N2O emissions from soils; whereas, the conversion of orchard residue into energy and C sequestration through soil amendment lead to a carbon credit of 100.3 Mg CO2-Ceq per year.;In conclusion, biochar did not decrease total N2O emissions from soils, but occasionally reduced N losses via leachate and improved plant utilization of N. A larger long-term environmental benefit of biochar was found to occur when using orchard residue for energy generation and C sequestration in soils.
机译：氮（N）管理对有机耕作系统构成​​挑战。特别是，不能总是实现足够的氮矿化，氮的释放时间和植物吸收的时间通常不同步，矿化的氮的后续N转化可能会作为环境污染物（例如沥滤的N和一氧化二氮（N2O）排放物）丢失。生物炭是在有限的氧气供应下通过生物质废物的热分解而得到的木炭，具有改变土壤理化性质以调节土壤氮保留的潜力。本论文评估了生物炭作为通过减少有机耕作系统改善氮素管理的一种手段。农业环境中氮的环境损失和氮的稳定化。以下三个实验使用多尺度方法研究了这些条件，包括农场试验和温室实验，温室气体（GHG）的高频评估，15N池稀释技术以及微生物分析。在代表有机莴苣生产系统的中观中，各种生物炭改良剂对植物性能，土壤特性和氮转化率的影响。在整个生长期监测N2O通量以及编码细菌硝化（amoA）和反硝化（nirK，nirS和nosZ）酶的功能基因。这项研究的结果表明，某些生物炭可能会加速有机肥中的氮矿化并增加净硝化作用。 N2O通量的减少仅在短期内观察到，并没有对总排放量产生重大影响。第二个实验研究了生物炭改良剂是否能减少土壤中氮的损失并改善植物的生长性能，以及这些影响是否与氮水平有关。肥料投入，收获时的氮输出，渗滤液和一氧化二氮的排放被用于评估生物炭改良土壤的氮利用和环境损失。在代表有机生菜生产系统的中观世界中，在两个生长季节中进行了这些评估。对植物性能的分析表明，生物炭改良剂并未使土壤施肥量少于商业施肥量（225 kg N ha -1）时植物生物量没有增加。在商业施肥速率下，生物炭提高了氮的利用效率（NUE），并通过淋滤减少了氮的损失，这导致氮损失与生物质中输出的氮的比率显着下降。仅在获得50％的商业施肥率（112 kg N ha-1）的土壤中，通过生物炭修正改变了N2O排放，这并没有改变氮素损失与生物质中输出的氮素的比率。农场对有机核桃园中生物炭改良土壤的温室气体排放进行了高频评估，此外还估算了将果园残渣转化为公用事业级能源所节省的温室气体。尽管观察到短期减少，但单独使用生物炭或与堆肥结合使用不会改变土壤中CO2和N2O的总排放量。然而，通过土壤改良将果园残余物转化为能量和固存碳，每年可产生100.3 Mg的二氧化碳当量碳当量。总之，生物炭不会减少土壤中的N2O排放总量，但偶尔会减少渗滤液中的氮损失当将果园残渣用于土壤中的能量产生和碳固存时，发现生物炭具有更大的长期环境效益。

著录项

  • 作者

    Pereira, Engil Isadora Pujol.;

  • 作者单位

    University of California, Davis.;

  • 授予单位 University of California, Davis.;
  • 学科 Agriculture Soil Science.;Biogeochemistry.;Sustainability.
  • 学位 Ph.D.
  • 年度 2014
  • 页码 130 p.
  • 总页数 130
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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