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Cropping systems and fertilization have important effects on soil organic carbon (OC) and nitrogen (N) turnover and availability; however, little information exists about the interaction of cropping system and fertilization. Herein, we analyzed the dynamics of soil OC and N in a 31-year experiment in a highland agroecosystem to understand how the effects of fertilization vary with cropping systems. The experiment included different cropping systems, and each system included various fertilization treatments. The cropping systems were continuous alfalfa (Medicago sativa L.), continuous winter wheat (Triticum aestivum L.), and grain-legume rotation of winter wheat + millet (Panicum miliaceum L.) - pea (Pisum sativum L.) - winter wheat. The fertilization treatments were the control (CK), phosphorous (P), P and nitrogen (NP) and NP and manure (NPM). A bare fallow treatment that did not receive any crop and fertilizer was designed to compare the effects of the cropping systems. The soil samples were collected at different times of the experiment. The contents of OC, N, and labile OC were measured, and the carbon management index was calculated. When averaged across the experimental periods, soil OC, N, labile OC and carbon management index were significantly higher in the pure legume (i.e., continuous alfalfa) system than in the bare fallow and nonlegume system (i.e., continuous winter wheat) due to the higher C and N inputs from root biomass. The NP and NPM significantly increased these soil variables, and the effects of NPM were greater than those of NP due to the higher supplying of C and N in NPM treatment than NP treatment. However, the effects of NP or NPM on soil OC and N contents were similar among the cropping systems. The effects of P were greater in the continuous alfalfa system but smaller in the continuous winter wheat system in comparison with those in the grain-legume rotation system. Therefore, at the conditions of our study, legume-included cropping systems with large root biomass and manure combined with chemical fertilizers have the potential to increase OC and N and their availability in highland soils, which could be important strategies for improving soil fertility and quality and sequestrating C in soils. Moreover, P fertilizer was recommended for the legume-included cropping systems. • We studied the effects of fertilization on soil OC and N in three cropping systems. • Continuous legume, continuous winter wheat and a grain-legume rotation were tested. • Legume increase soil OC and N and their availability. • Effects of NP or NP combined with manure were similar among cropping systems. • Effects of chemical P fertilizer on soil OC and N varied with cropping systems. [ABSTRACT FROM AUTHOR]

Estimating regional carbon (C) stocks and understanding their dynamics is crucial, both from the perspective of sustainable landscape management and global change feedback. This study combines remote sensing techniques and a coupled GIS-CENTURY model to estimate regional biomass C stocks and SOC dynamics for Guiera senegalensis shrub communities in Senegal''s Peanut Basin. A statistical model relating field-measured shrub aboveground biomass C at training plots to satellite image-derived shrub abundances was developed and used to estimate regional biomass C across a major part of the Basin. Regional SOC dynamics were modeled by coupling the CENTURY model and GIS databases. Significant correlation (r =0.73; p =0.05) was observed between aboveground biomass C and satellite image-derived shrub abundance at the training plots. Aboveground biomass C stocks ranged from 0.01 to 0.45Mgha−1 with an approximate total of 247,000MgC for the 3060km2 study area. CENTURY model predictions indicate that C sequestration in these systems is contingent on long-term effectiveness of non-thermal management of shrub residue and that the actual rates depend strongly on soil type and scenarios of future land management. Compared with the traditional “pruning-burned” management practice, returning prunings for 50 years would increase soil C sequestration by 200–350% without fertilization, and increase soil C sequestration by 270–483% under a low (35kgha−1 Nyr−1; 20kgha−1 Pyr−1) fertilization regime, depending on soil type and climate conditions. These results indicate that altered land management could contribute to transforming these degraded semiarid agroecosystems from a source to a sink for atmospheric CO2. [Copyright &y& Elsevier]