Biochar is purported to provide agricultural benefits when added to the soil, through changes in saturated hydraulic conductivity (K_sat) and increased nutrient retention through chemical or physical means. Despite increased interest and investigation, there remains uncertainty regarding the ability of biochar to deliver these agronomic benefits due to differences in biochar feedstock, production method, production temperature, and soil texture. In this project, a suite of experiments was carried out using biochars of diverse feedstocks and production temperatures, in order to determine the biochar parameters which may optimize agricultural benefits. Sorption experiments were performed with seven distinct biochars to determine sorption efficiencies for ammonium and nitrate. Only one biochar effectively retained nitrate, while all biochars bound ammonium. The three biochars with the highest binding capacities (produced from almond shell at 500 and 800 ^∘C (AS500 and AS800) and softwood at 500 ^∘C (SW500)) were chosen for column experiments. Biochars were amended to a sandy loam and a silt loam at 0 % and 2 % ($w/w$), and K_sat was measured. Biochars reduced K_sat in both soils by 64 %–80 %, with the exception of AS800, which increased K_sat by 98 % in the silt loam. Breakthrough curves for nitrate and ammonium, as well as leachate nutrient concentration, were also measured in the sandy loam columns. All biochars significantly decreased the quantity of ammonium in the leachate, by 22 % to 78 %, and slowed its movement through the soil profile. Ammonium retention was linked to high cation exchange capacity and a high oxygen-to-carbon ratio, indicating that the primary control of ammonium retention in biochar-amended soils is the chemical affinity between biochar surfaces and ammonium. Biochars had little to no effect on the timing of nitrate release, and only SW500 decreased total quantity, by 27 % to 36 %. The ability of biochar to retain nitrate may be linked to high micropore specific surface area, suggesting a physical entrapment rather than a chemical binding. Together, this work sheds new light on the combined chemical and physical means by which biochar may alter soils to impact nutrient leaching and hydraulic conductivity for agricultural production.

中文翻译：

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生物炭改变两种农业土壤的导水率并影响养分浸出

据称，当将生物炭添加到土壤中时，通过改变饱和导水率（K _sat) 并通过化学或物理方式增加营养保留。尽管兴趣和调查增加，但由于生物炭原料、生产方法、生产温度和土壤质地的差异，生物炭提供这些农艺效益的能力仍存在不确定性。在该项目中，使用不同原料和生产温度的生物炭进行了一系列实验，以确定可以优化农业效益的生物炭参数。用七种不同的生物炭进行吸附实验，以确定铵和硝酸盐的吸附效率。只有一种生物炭有效地保留了硝酸盐，而所有生物炭都结合了铵。结合能力最高的三种生物炭（由杏仁壳在 500 和 800  ^∘C（AS500和AS800）和软木在500  ^∘ C（SW500））被选择用于柱的实验。生物炭被修改为砂壤土和粉砂壤土，分别为 0 % 和 2 % ($瓦/瓦$)，并 测量了K _sat。生物炭将两种土壤中的K _sat降低了 64%–80%，但 AS800 除外，它增加了K _sat98% 在粉砂壤土中。在砂壤土柱中还测量了硝酸盐和铵的突破曲线以及渗滤液养分浓度。所有生物炭都显着降低了渗滤液中铵的含量，从 22% 到 78%，并减缓了其在土壤剖面中的移动。铵保留与高阳离子交换能力和高氧碳比有关，表明生物炭改良土壤中铵保留的主要控制是生物炭表面与铵之间的化学亲和力。生物炭对硝酸盐释放的时间几乎没有影响，只有 SW500 使总量减少了 27% 到 36%。生物炭保留硝酸盐的能力可能与高微孔比表面积有关，这表明是物理捕获而不是化学结合。一起，