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Carbon pools and soil biochemical properties in manure‐based organic farming systems of semi‐arid New Mexico

Jacinthe, P.‐A., Shukla, M. K., Ikemura, Y.
Soil use and management 2011 v.27 no.4 pp. 453-463
Gossypium arboreum, ammonium nitrate, animal wastes, carbon sequestration, carbon sinks, correlation, cotton, irrigated farming, land application, microbial biomass, nutrients, organic production, production technology, soil biological properties, soil microorganisms, soil organic carbon, soil respiration, urea, New Mexico
The economic benefits of organic agriculture and its wide adoption are well documented, but the impact of that practice on soil C dynamics in irrigated croplands of semi‐arid regions is less well understood. In manure‐based organic production systems, land applications of animal wastes not only provide nutrients but could also contribute to soil carbon sequestration. A study was conducted in irrigated cotton (Gossypium arboreum L) agro‐ecosystems of New Mexico (USA) under conventional (CONV; 100 kg N/ha as urea and NH4NO3) and organic farming practices (OF for 3–9 yr; 50 Mg dry manure/ha) to assess the effect of OF on soil C stocks (organic, inorganic) and biochemical indices [microbial biomass C (MBC); respiration; metabolic quotient (qCO2)]. In the plough layer (0–30 cm), soil organic carbon (SOC) stocks tended to be higher (although not statistically) under OF (35.9 Mg C/ha) than CONV (33.5 Mg C/ha). However, when the entire 100‐cm soil profile was considered, the total SOC under CONV exceeded that under OF by 39.8 Mg C/ha, but this may be influenced by other factors. Accounting for 52% of the total C stock, inorganic C was significantly higher under CONV than OF and was positively correlated with soil respiration and the H/C ratio of soil organic matter. While OF duration had no consistent effect on soil biochemical properties, MBC was significantly higher (1.5 times) and the qCO2 (3–6 times) was lower in the organically fertilized soils than under CONV. These results suggest the development, under OF, of a soil microbial community that is larger and processes added C substrates more efficiently compared with the community present in CONV practices.