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The maximum power tracking of Proton Exchange Membrane Fuel Cells (PEMFC) is important for the optimization of fuel cell system design. It is necessary to operate a fuel cell at maximum power to ensure full efficiency. This study presents a novel Fractional Order Incremental Conductance Algorithm (FOINC) with variable step size control which can be used for maximum power point tracking in the design of fuel cells. The method has high maximum power point tracking speed and good steady-state response, and does not require extra sensing elements for different fuel cell equipment. When compared to the traditional Incremental Conductance (INC) and Perturbation and Observation (P&O) methods, the system simulation results show the method to be feasible and effective.

Revegetation facilitated by legume species introduction has been used for soil erosion control on the Loess Plateau, China. However, it is still unclear how vegetation and soil resources develop during this restoration process, especially over the longer term. In this study, we investigated the changes of plant aboveground biomass, vegetation cover, species richness and density of all individuals, and soil total nitrogen, mineral nitrogen, total phosphorus and available phosphorus over 11 years from 2003 to 2013 in three treatments (natural revegetation, Medicago sativa L. introduction and Melilotus suaveolens L. introduction) on the semi-arid Loess Plateau. Medicago significantly increased aboveground biomass and vegetation cover, and soil total nitrogen and mineral nitrogen contents. The Medicago treatment had lower species richness and density of all individuals, lower soil moisture in the deep soil (i.e., 1.4-5m), and lower soil available phosphorus. Melilotus introduction significantly increased aboveground biomass in only the first two years, and it was not an effective approach to improve vegetation biomass and cover, and soil nutrients, especially in later stages of revegetation. Overall, our study suggests that M. sativa can be the preferred plant species for revegetation of degraded ecosystems on the Loess Plateau, although phosphorus fertilizer should be applied for the sustainability of the revegetation.

Many studies have reported evidence describing the effects of K2SO4 fertilizer on crop productivity, but there is scant information about the yield-increasing mechanisms when influencing soil properties by K2SO4 application in calcareous and alkaline soils. In this study, one field and incubation experiments were conducted to investigate the effects of K2SO4 fertilizer on crop yields and soil properties in calcareous and alkaline soils on the Loess Plateau of Northwestern China. In field experiments, four K2SO4 treatments were applied to potato (Solanum tuberosum L.) in 2007 and spring wheat (Triticum aestivum L.) in 2008: (1) CK: no K2SO4; (2) T1: K2SO4 @ 100 kg ha−1 in 2007 and 50 kg ha−1 in 2008; (3) T2: K2SO4 @ 200 kg ha−1 in 2007 and 100 kg ha−1 in 2008; and (4) T3: K2SO4 @ 300 kg ha−1 in 2007 and 150 kg ha−1 in 2008. In 2007, potato yield increased by 17.4% in T2 and 21.5% in T3 compared with CK, but did not significantly increase in T1. In 2008, spring wheat yields increased by 10.0%, 15.8% and 18.7% in T1, T2 and T3 treatments, respectively, compared with CK. Stepwise regression (P ≤ 0.05) revealed that soil-available K at tuber formation and starch accumulation stage, and available P at starch accumulation stage correlated well with potato yield. Soil available P before sowing and at anthesis correlated well with spring wheat yield. Soil available P content was mostly higher in T1, T2 and T3 than in CK from June 2007 to August 2008 when the same dose P fertilizer was applied in all plots. Applying K2SO4 decreased soil pH. Soil available P was significantly negatively correlated with soil pH (R = –0.5721, P = 0.0015). In an incubation experiment, the four K2SO4 treatments were designed: (1) CK: no K2SO4; (2) S1: K2SO4 @ 0.44 g kg−1 dry soil; (3) S2: K2SO4 @ 0.88 g kg−1 dry soil; (4) S3: K2SO4 @ 1.32 g kg−1 dry soil. The results also showed that addition of K2SO4 significantly decreased soil pH and increased available P in calcareous and alkaline soils. Our study suggests that K2SO4 is desirable for improving crop productivity by increasing soil P availability via decreasing soil pH in calcareous and alkaline soils besides K effect in a low input dryland agroecosystem.