Soil Organic Carbon Dynamics under Short-term Conservation Agriculture Cropping Systems in Cambodia

Land degradation has been gradually expanded in Cambodia due to improper agricultural management practices. Conservation agriculture (CA) is a potential set of management practices to restore soil total N (STN), soil organic C (SOC) and SOC labile fractions (i.e., particulate organic C-POC, hot-water extractable organic C-HWEOC, permanganate oxidizable C-POXC), to increase soil enzyme activities and to enhance soil aggregation. This study aims at quantifying the changes in soil organic C, nitrogen, labile-C fractions, enzymatic activities and soil aggregation under conventional plow-based and no-till cropping systems for a Red Oxisol in Cambodia.

Three randomized block design experiments were implemented in 2009 at the Bos Khnor experimental Station (Kampong Cham province, Cambodia, 12°12′33″N and 105°19′19″E,  119 m asl), and each trial is dedicated to one rainfed staple and commercial crops of the region: cassava (Manihot esculenta), soybean (Glycine max), and rice (Oryza sativa). Maize (Zea mays), cropped on more than 300,000 ha in Cambodia is also included in the rotational sequence. Each experiment comprises seven tillage systems, implemented on 8.0 × 37.5 m plots (300 m2), according to a randomized complete block design, with three replicates, covered a total area of 2.5 ha. Four treatments were selected for former studies and consisted in: (1) conventional tillage based systems where the key crops are conducted in annual succession for rice and soybean (i.e., mungbean/rice – CT-R, sesame/soybean – CT-S) and mono-cropping for cassava (CT-C), (2) DMC based systems where key crops (i.e., rice, soybean, and cassava) are grown in a one year frequency pattern (NT1-R, NT1-S, NT1-C), and (3) DMC based systems where key crops are grown in bi-annual rotations with maize, the 2 plots in these bi-annual rotations being NT2-R, NT3-R for rice, NT2-S, NT3-S for soybean and NT2-C, NT3-C for cassava. In NT1, NT2 and NT3, Stylosanthes guianensis is used as cover crop and grown in association with the main annual crop. Conventional tillage (CT) is operated prior to each crop with a 7 discs plow pulled by an 80 horse power (HP) tractor.









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