ABSTRACT

Humic substances are increasingly used as biostimulants in agriculture because of their supposed effects on nutrient uptake and crop yield. The objective of this study was to assess the effect of fulvic acid (FA) and humic acid (HA) addition with and without fertilization (N, P, K, S, and Ca) on (i) grass yield (Poa trivialis) and nutrient uptake and (ii) composition of soil porewater and 0.01 M CaCl₂ soil extracts. Therefore, a pot experiment was performed using a loamy soil and a non-calcareous sandy soil. Fertilization increased N and P uptake and grass yield but there was no effect of FA or HA application (200 mg C kg⁻¹ soil) regardless of whether N or P was the growth limiting nutrient. Nutrient availability was assessed in soil pore water samples extracted by centrifugating moist soil and by 0.01 M CaCl₂ extracts of oven-dried soil. HA and FA had no effect on the availability of NO₃ or ortho-P, neither in soil porewater nor in 0.01 M CaCl₂ soil extracts. Fertilization led to an increase in 0.01 M CaCl₂-extractable ortho-P but, remarkably, to a decrease in ortho-P and Dissolved Organic Carbon (DOC) concentrations in soil pore water samples. This discrepancy was explained by the higher ionic strength of pore water in the fertilized soils, which caused the pH to drop by 0.2 to 0.4 units and thereby stimulated adsorption of ortho-P and DOC to reactive soil minerals. Such salt-induced effects do not occur in 0.01 M CaCl₂ soil extracts where the ionic strength is nearly constant.

摘要

腐殖质越来越多地用作农业中的生物刺激剂，因为它们对养分吸收和作物产量有影响。本研究的目的是评估在施肥和不施肥（N、P、K、S 和 Ca）的情况下添加富里酸 (FA) 和腐植酸 (HA) 对 (i) 草产量（Poa trivialis）和养分吸收和 (ii) 土壤孔隙水和 0.01 M CaCl ₂土壤提取物的组成。因此，使用壤土和非钙质沙土进行盆栽试验。施肥增加了 N 和 P 的吸收和草产量，但 FA 或 HA 的应用（200 mg C kg ^-1土壤），无论 N 还是 P 是生长限制养分。在通过离心潮湿土壤和烘干土壤的0.01 M CaCl ₂提取物提取的土壤孔隙水样品中评估养分有效性。HA 和 FA 对 NO ₃或邻磷的有效性没有影响，无论是在土壤孔隙水中还是在 0.01 M CaCl ₂土壤提取物中。施肥导致 0.01 M CaCl ₂增加-可提取的邻磷，但显着地降低了土壤孔隙水样品中的邻磷和溶解有机碳 (DOC) 浓度。造成这种差异的原因是施肥土壤中孔隙水的离子强度较高，这导致 pH 值下降 0.2 至 0.4 个单位，从而刺激了原磷和 DOC 对活性土壤矿物质的吸附。在离子强度几乎恒定的0.01 M CaCl ₂土壤提取物中不会发生这种盐诱导的影响。