Seasonal Changes in Soil Organic Matter and Biomass and Labile Forms of Carbon as Influenced by Crop Rotations

Abstract

Recent concerns about the role of carbon (C) in climate change and the implications about soil organic matter (SOM) for sustainable use of soils have underlined the need to examine the role of SOM in cropping systems, particularly in fragile ecosystems. Accordingly, we examined the changes that occur in total SOM and in its more reactive fractions, labile and biomass C, within a long-term, cereal-based crop rotation trial. The rotations were wheat (Triticum turgidum var durum) grown after vetch (Vicia sativa), medic (Medicago sativa), chickpea (Cicer arietinum), lentil (Lens culinaris), fallow, a summer crop, melon (Citrullus vulgaris), and after wheat (i.e., continuous wheat). Secondary treatments involved nitrogen (N) fertilizer application and variable grazing intensity. Uncropped microplots were established in the main rotation plots, and in the fallow and medic ones with variable grazing. Total SOM and labile and microbial biomass C were periodically measured in the rotations throughout the cropping season. Medic and vetch were highest in the three C forms, with fallow always lowest. All forms changed with sampling time throughout the season. Organic matter decreased from 1.48% in February to 1.15% in August after cropping. Although labile C followed a similar pattern, with a large falloff between the May and August sampling, biomass C increased initially, remained stable for a few months, and decreased at the last two samplings. Although all three C forms were highest in the zero-grazing in the fallow and medic rotations, the effect of grazing was not significant. Thus, although organic C can be built up in the soil to varying extents

Seasonal Changes of Soil Quality Indicators in Selected Arid Cropping Systems

“…The SOM and POXC, which are indicators of the soil organic carbon, were the highest in winter and fall, and may have accumulated because of a low soil temperature, lack of soil disturbance that would expose the organic matter to oxidation, and lower microbial activity resulting in less consumption of soil organic products for energy. This result is confirmed by other studies that have found a significantly higher SOM and microbial biomass carbon in winter compared with summer [10,11]. Although the decomposition rate is slower during this period, the enzyme and microbial activities in early fall, and the plant carbon inputs and litter chemistry in winter may have increased the soil's carbon concentration [26][27][28].…”

“…Previous studies have shown the variability that could exist, as soil quality indicators are sampled during the different months of the year within a given growing season [8][9][10][11]. Moebius et al [8] studied the temporal variations of many soil physical quality indicators within a season, in different tillage and crop rotation trials, and found that the indicators vary significantly with the sampling dates and in the different soil types.…”

“…They also found that the microbial biomass carbon was the highest in winter and the lowest in the summer. Ryan et al [10] studied the changes in the total soil organic matter, labile carbon, and microbial biomass carbon during the season. They found that the organic matter decreased from 1.48% in February to 1.15% in August after cropping.…”

Climate Change and Food Security in West Asia and North Africa

“…Further, cereal-legume rotations, while being biologically and economically attractive, also improve soil quality and advance agronomic sustainability in the harsh dryland conditions of the WANA region . The labile fraction decreased from 1,746 mg kg −1 in February to 1,275 mg kg −1 in August, and the MBC from 107 mg kg −1 in February to 71 mg kg −1 in August (Ryan et al 2009 ). The SOM concentration in the surface and sub-soil respectively, was 1.4 % and 1.1 % in medic ( Medicago spp.)…”

“…A long-term experiment at Tel Hadya, Syria showed that soil physical properties indicated parallel trends with increasing concentration of SOM . Ryan et al ( 2009 ) observed that the SOM concentration decreased from 1.48 % in February to 1.151 % in August after cropping. Kapur et al ( 2007 ) assessed the impact of several cereal-based rotations on soil quality in Aleppo, Syria.…”