ABSTRACT

Rice cultivation and ruminants are the top two sources of methane (CH₄), a potent greenhouse gas, in agriculture. The supplementation of ruminants with cashew nut shell liquid (CNSL), a by-product of the cashew nut industry, can reduce CH₄ production through alteration of the rumen microbiota. To assess the effects of CNSL addition and its rate on rice growth and CH₄ emissions from a paddy soil, we carried out four experiments. CNSL was added at 0 (control) to 1000 ppm by volume in water or agar. In 3-week in vitro anaerobic incubation of two soils, Fluvisol and Andosol, CNSL significantly (P < 0.05) reduced CH₄ production dose-dependently, by 54–61% at 1000 ppm relative to the control. In 7-day seed germination testing, CNSL concentration did not affect the final germination percentage (96–99%). In 19-day early seedling growth, CNSL significantly increased the maximum root length by the same amount at all concentrations. In addition, the number of root hairs notably increased with increasing CNSL concentration. In pot culture of rice, the seasonal total CH₄ emission was not affected by CNSL concentration. However, mixing CNSL at 1000 ppm with soil before transplanting tended to reduce the initial 30-day CH₄ emission by 41%, whereas addition to surface water after plant establishment had no effect. Rice plant growth and dry matter production in pot cultivation were not affected by CNSL concentration. Altogether, the results indicate that CNSL addition can reduce CH₄ production in a flooded paddy soil without major harm to rice growth. It is necessary to develop an effective method for the application of CNSL to paddy fields for enhancing the inhibitory effect of CNSL on soil CH₄ emission.

摘要

水稻种植和反刍动物是农业中甲烷 (CH ₄ )（一种强效温室气体）的两大来源。向反刍动物补充腰果壳油 (CNSL) 是腰果工业的副产品，可以通过改变瘤胃微生物群来减少 CH _{4 的}产生。为了评估 CNSL 添加及其速率对水稻生长和稻田CH ₄排放的影响，我们进行了四个实验。在水或琼脂中以 0（对照）至 1000 ppm（体积）的方式添加 CNSL。在Fluvisol 和Andosol 两种土壤的体外厌氧培养3 周中，CNSL 显着( P < 0.05) 降低了CH ₄产生剂量依赖性，在 1000 ppm 时相对于对照增加 54-61%。在 7 天种子发芽试验中，CNSL 浓度不影响最终发芽率（96-99%）。在 19 天的早期幼苗生长中，CNSL 在所有浓度下显着增加了相同的最大根长度。此外，根毛的数量随着 CNSL 浓度的增加而显着增加。在水稻盆栽中，季节性总 CH ₄排放不受 CNSL 浓度的影响。然而，在移栽前将 1000 ppm 的 CNSL 与土壤混合往往会降低最初 30 天的 CH ₄排放量增加了 41%，而植物建立后添加到地表水没有影响。盆栽栽培中的水稻植株生长和干物质产量不受 CNSL 浓度的影响。总之，结果表明添加 CNSL 可以减少淹水稻田中CH _{4 的}产量，而不会对水稻生长造成重大危害。有必要开发一种有效的方法将CNSL应用于稻田，以增强CNSL对土壤CH ₄排放的抑制作用。