Purpose

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 methods

There 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 discussion

The 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.

Conclusions

Corn 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.

目的

腐殖质是总有机碳（TOC）的组成部分，会影响土壤质量。该研究旨在调查腐殖质和非腐殖质级分是否表现出早期，一致和可测量的变化，并在用玉米芯生物炭改良的热带沙壤土中影响TOC敏感性和储存。

材料和方法

在随机完整区组设计中建立了四次重复的四种治疗方法。复合土壤样品取自无生物炭（CT）的地块，掺有15 t生物炭ha ^-1（BC-15）和30 t生物炭ha ^-1的无或有磷肥的地块（BC-30和BC-30 + P）。确定每种处理的土壤有机碳的TOC以及腐殖质，腐殖酸（HA）和黄腐酸（HA）的分数。用分光光度法测量无土壤提取物的光密度（400-700 nm）；使用在465和665 nm处测得的密度来计算E ₄₆₅ / E ₆₆₅比值。

结果与讨论

BC-30和BC-30 + P图记录了最高的TOC，腐殖质，腐殖酸（HA）和富里酸（FA）含量，而CT值最低。相对于CT，在所有生物炭处理过的样地中，总可交换碳分层明显更高。谱分析表明的较高的值ë ₄₆₅ / ë ₆₆₅分别（5.02和5.15）在CT和BC-15处理过的土壤中，与和BC-30和BC-30 + P-修正土壤相比ë ₄₆₅ / ë ₆₆₅比分别为2.76和2.98。

结论

玉米芯生物炭应用于热带沙质壤土：

•增加HA和FA的浓度，导致TOC分层增加，与FA相比，对HA的作用更强；

•在30 t ha ^-1的高生物炭施用率下，E ₄₆₅ / E ₆₆₅显着降低，这意味着高分子量类腐殖酸类物质占主导地位，TOC的芳香度增加。