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Humic substances, which are integral components of total organic carbon (TOC), influence soil quality. The study aimed to investigate whether humic and non-humic fractions exhibit early, consistent, and measurable changes and affect TOC sensitivity and storage in a tropical sandy loam soils amended with corn cob biochar.
Materials and methodsThere were four treatments with four replicates established in a randomized complete block design. Composite soil samples were taken from plots without biochar (CT), from plots incorporated with 15 t biochar ha?1 (BC-15), and 30 t biochar ha?1 without or with phosphate fertilizer (BC-30 and BC-30+P). The TOC, and humin, humic acid (HA), and fulvic acid (HA) fractions of soil organic carbon were determined for each treatment. The optical densities (400–700 nm) were measured on the soil-free extracts by spectrophotometry; the densities measured at 465 and 665 nm were used to calculate the E465/E665 ratios.
Results and discussionThe BC-30 and BC-30+P plots recorded the highest TOC, humin, humic acid (HA), and fulvic acid (FA) contents with respect to the lowest in the CT. The total exchangeable carbon stratification was significantly higher in all the biochar-treated plots relative to the CT. Spectral analysis showed higher values of E465/E665 (5.02 and 5.15) in the CT and BC-15-treated soils, respectively, compared with the BC-30 and BC-30+P-amended soils with E465/E665 ratios of 2.76 and 2.98, respectively.
ConclusionsCorn cob biochar applied to a tropical sandy loam:
? increased the concentrations of HA and FA and led to increased stratification of TOC, with a stronger effect on HA compared with FA;
? significantly lowered E465/E665 at the high biochar application rate of 30 t ha?1, implying the dominance of high molecular weight humic acid-like substances, and increased degree of aromaticity of the TOC.
相似文献Grid sampling allows a variable rate of lime to be applied and has been marketed as a cost saver to producers. However, there is little research that shows if this precision application is profitable or not. Previous research on variable-rate lime has considered only a small number of fields. This paper uses soil sampling data from 111 fields provided by producers in Oklahoma and Kansas. The 5-year average net present values are compared between variable-rate and uniform-rate lime for grain-only wheat production, dual-purpose wheat grain and forage production, and a wheat–soybean rotation. Sensitivity analysis was done for varying grain prices as well as grain yield potential. When using historical average yields and recent prices for Oklahoma, variable rate was not profitable on average for these 111 fields for either a grain-only, dual-purpose, or wheat–soybean production. However, when yield or prices were above average, variable rate was profitable. Thus, variable rate liming can be profitable for these fields, but it requires either above average yields, a high value crop, or above average prices.
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