University of Khartoum

Soil Organic Matter Fractions under Rain-fed and Irrigated Long-term Cropping Systems in the Vertisols of Sudan

Soil Organic Matter Fractions under Rain-fed and Irrigated Long-term Cropping Systems in the Vertisols of Sudan

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Title: Soil Organic Matter Fractions under Rain-fed and Irrigated Long-term Cropping Systems in the Vertisols of Sudan
Author: Abdalla, Mubarak Abdelrahman
Abstract: The content of soil organic matter (SOM) in the soil is one of the important indices of soil quality. Attempts to fractionate (either by size or density) SOM in the vertisols of Sudan have never been carried out. Our objectives were to determine dry matter weight (DM), C and N contents of particulate organic matter (POM) in different long term (> 40 years) cropping systems. Soil samples (0-20 cm) were collected from: (1) continuous alfalfa (Medicago sativa L.) (CL) (2) a rotation of faba bean (Vicia faba) or wheat (Triticum aestivum) (in winter) and sorghum (Sorghum bicolor L.) in summer (W/F-S) (3) a rotation of cotton (Gosypium hirsuturn) - wheat- groundnut (Arachis hypogaea)— sorghum - fallow (C-W-G-S-F) and (4) a rain-fed area, mainly: continuous sesame (Sesamum indicum) (CSe), continuous sorghum (CSo.) and a rotation of sesame with sorghum (Se-So). Samples from native vegetation (NV) were .also.collected (reference) from rain-fed and irrigated areas. A wide level disc was the only tillage implement used in the rain-fed areas compared to conventional tillage (disc plough, disc harrowing, levelling and ridging) in the irrigated areas with sub-soiling in a 5 year period. Results showed that, in the irrigated fields, content of POM under NV management system (23.16-27.70 gke) was significantly (F`50.01) higher than that reported under cultivated land (6.09 —8.25 gke). However, in rain-fed areas, the rotation of the Se-So had a significantly higher POM (6.9 gkg-I) compared to NV (5.53 gke) and CSe or CSo (2.77— 2.78 gke). Content of POM under irrigated cropping systems (7.25 gke) was almost doubled compared to its content in rain-fed areas (4.15 gkg-1). Generally, cultivating the soil (under rain:fed or irrigation) significantly decreased POM content from 18.8 gkg1 to 5.7 gke (i.e. by 70%). Contents of N and C of POM were significantly higher under NV management systems compared to cultivated land. It could be concluded that, to improve the quality of vertisols in the semi-arid tropics with fast decomposition of added organic matter (low rate of C sequestration), it is necessary to increase return of crop residues to the soil for better build of soil organic matter.
URI: http://khartoumspace.uofk.edu/123456789/22235


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