Carbon accumulation in cotton, sorghum, and underlying soil as influenced by tillage, cover crops, and nitrogen fertilization

Abstract

Soil and crop management practices may influence biomass growth and yields of cotton (Gossypium hirsutum L.) and sorghum (Sorghum bicolorL.) and sequester significant amount of atmospheric CO₂in plant biomass and underlying soil, thereby helping to mitigate the undesirable effects of global warming. This study examined the effects of three tillage practices [no-till (NT), strip till (ST), and chisel till (CT)], four cover crops [legume (hairy vetch) (Vicia villosa roth), nonlegume (rye) (Secale cerealeL), hairy vetch/rye mixture, and winter weeds orno covercrop], and three N fertilization rates (0, 60–65, and 120–130 kg N ha ⁻¹) on the amount of C sequestered in cotton lint (lint + seed), sorghum grain, their stalks (stems + leaves) and roots, and underlying soil from 2000 to 2002 in central Georgia, USA. A field experiment was conducted on a Dothan sandy loam (fine-loamy, kaolinitic, thermic, Plinthic Kandiudults). In 2000, C accumulation in cotton lint was greater in NT with rye or vetch/rye mixture but in stalks, it was greater in ST with vetch or vetch/rye mixture than in CT with or without cover crops. Similarly, C accumulation in lint was greater in NT with 60 kg N ha ⁻¹ but in stalks, it was greater in ST with 60 and 120 kg N ha ⁻¹ than in CT with 0 kg N ha ⁻¹. In 2001, C accumulation in sorghum grains and stalks was greater in vetch and vetch/rye mixture with or without N rate than in rye without N rate. In 2002, C accumulation in cotton lint was greater in CT with or without N rate but in stalks, it was greater in ST with 60 and 120 kg N ha ⁻¹ than in NT with or without N rate. Total C accumulation in the above- and belowground biomass in cotton ranged from 1.7 to 5.6 Mg ha ⁻¹ and in sorghum ranged from 3.4 to 7.2 Mg ha ⁻¹. Carbon accumulation in cotton and sorghum roots ranged from 1 to 14% of the total C accumulation in above- and belowground biomass. In NT, soil organic C at 0–10 cm depth was greater in vetch with 0 kg N ha ⁻¹ or in vetch/rye with 120–130 kg N ha ⁻¹ than in weeds with 0 and 60 kg N ha ⁻¹ but at 10–30 cm, it was greater in rye with 120–130 kg N ha ⁻¹ than in weeds with or without rate. In ST, soil organic C at 0–10 cm was greater in rye with 120–130 kg N ha ⁻¹ than in rye, vetch, vetch/rye and weeds with 0 and 60 kg N ha ⁻¹. Soil organic C at 0–10 and 10–30 cm was also greater in NT and ST than in CT. Since 5 to 24% of C accumulation in lint and grain were harvested, C sequestered in cotton and sorghum stalks and roots can be significant in the terrestrial ecosystem and can significantly increase C storage in the soil if these residues are left after lint or grain harvest, thereby helping to mitigate the effects of global warming. Conservation tillage, such as ST, with hairy vetch/rye mixture cover crops and 60–65 kg N ha ⁻¹ can sustain C accumulation in cotton lint and sorghum grain and increase C storage in the surface soil due to increased C input from crop residues and their reduced incorporation into the soil compared with conventional tillage, such as CT, with no cover crop and N fertilization, thereby maintaining crop yields, improving soil quality, and reducing erosion.