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Abstract Nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) could be used to reduce nitrogen (N) loss and improve N use efficiency in agroecosystems. However, the DMPP effect on N dynamics at the microscale remains largely unknown. A microcosm experiment was conducted to evaluate the effects of DMPP and fertilizer application method on N fate, including 15NH 4 +-N, (15NO 3 −+15NO 2 −)-N, MB15N and N losses at the centimeter-scale. The isotope labelled 15N-urea was applied to soil with or without DMPP. Two fertilizer application methods were compared, including mixed with soil (mix-application) or concentrated on the soil surface (spot-application). After 28 days of incubation at 28 °C, DMPP amended with urea significantly increased soil pH and 15NH 4 +-N concentrations but decreased (15NO 3 −+15NO 2 −)-N concentrations in both horizontal and vertical directions compared with urea application alone. Such effect was more obvious within 0–2 cm and weakened with increasing distance from the fertilizer zone. DMPP addition significantly increased N losses compared with urea application alone, which is mainly due to the increased ammonia volatilization caused by high pH and NH 4 + concentrations. The application method of urea and DMPP also had different effects on N performance, depending on the distance and spatial directions of microsites. And the N losses in the mix-application treatment (32%) were significantly lower than in the spot-application treatment (37%) when urea was applied alone. We concluded that DMPP addition significantly slowed down nitrification processes, and urea mixed with soil is better than concentrated on the soil surface in reducing N losses when urea was applied alone. Highlights • DMPP increased NH 4 +-N but decreased (NO 3 − + NO 2 −)-N concentrations at the microscale. • Nitrification inhibition was more evident within 0–2 cm from fertilization zone. • The efficiency of DMPP was weakened with the increasing distance. • Urea mixed with soil was better than spot on the soil surface in reducing N loss. [ABSTRACT FROM AUTHOR]

Nematodes exert top-down control on the microbially-mediated processes of decomposition and nutrient cycling due to their position in the soil food web. Fertilization of agricultural soils can increase substrates for nematode populations, but whether the nematode community response to fertilization is consistent under anaerobic and aerobic soil conditions is not known. Our study investigated how soil nematode abundance and community structure responded to fertilization of a double-cropping system with paddy rice, representing anaerobic soil conditions due to flooding, followed an upland wheat phase that was rainfed and predominantly aerobic. We examined nematode communities twice a year from 2011 to 2013 at the ripening stage of rice (October) or wheat (June). Five fertilizer treatments were compared, including control (CK), chemical fertilizer (CF), compound pig manure-chemical fertilizer (MCF), straw plus chemical fertilizer (SCF) and pig manure plus straw plus chemical fertilizer (MSCF). Total nematode abundance increased by fertilization consistently in the rice and wheat cropping phases, and straw addition (i.e. SCF and MSCF) showed higher increment than manure addition (i.e. MCF) and CF treatments. However, dominant nematode genera respond to fertilization differently, depending on the crop phase. This is because dominant genera in the anaerobic soils of the rice phase were the plant-feeding nematode Hirschmanniella and algae-feeding nematode Rhabdolaimus , whereas dominant genera in the aerobic soils of the wheat phase were the fungal-feeding nematode Filenchus and bacterial-feeding nematodes Cephalobus , Eucephalobus and Acrobeloides . The manure addition (i.e. MCF) significantly raised Hirschmanniella abundance (by 133–616%) but sharply reduced the Rhabdolaimus population by 115–774% in the rice phase. In addition, straw addition (i.e. SCF and MSCF) increased Filenchus numbers (18–118%) but decreased the Acrobeloides population (49–145%) in the wheat phase. Since the MCF, SCF and MSCF fertilizers supply organic substrates for microbes and nutrients for plants, both of which are consumed by nematodes, this implies that food resources are the key determinant of total nematode abundance, the population size of all trophic levels. Our findings show that the nematode community structure is distinctive for each crop grown under a particular soil moisture regime, and that food resources derived from fertilizer inputs act as a bottom-up modulator of nematode population size in paddy rice–upland wheat systems. [ABSTRACT FROM AUTHOR]