Search

Abstract: The effect of earthworms on humus composition and humic acid (HA) characteristics was studied in a rice–wheat rotation agroecosystem. Experimental plots in the rotation had five treatments, i.e., incorporation or mulching of maize residues with or without added earthworms and a control. Compared with the control, the application of maize residues to soil either alone or in combinations with earthworms strongly affected the humus composition and HA characteristics. In the presence of earthworms, the carbon ratio of HA to fulvic acid (FA), and the alkyl C/O-alkyl C and hydrophobic C/hydrophilic C ratios of HA were slightly higher, while the aliphatic C/aromatic C ratio of HA was slightly lower following maize residue incorporation than the same treatment without earthworms. In contrast, these ratios generally remained almost constant following maize residue mulching. Thus, earthworm activity following maize residue incorporation was more favorable for the HA formation, and was associated with a decrease in aliphaticity of HA, and an increase in its degree of humification and hydrophobicity. [Copyright &y& Elsevier]

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]

Abstract: The effect of earthworms on soil hydrolases (protease, urease, invertase, and alkaline phosphatase) and dehydrogenase activities was investigated in maize residue amended rice–wheat rotation agro-ecosystem. Experimental plots in the rotation had five treatments, i.e. incorporation or mulching of maize residues with or without added earthworms and an untreated control. The application of maize residues to soil without earthworms significantly enhanced the five soil enzyme activities compared with the control treatment during rice and wheat cultivation. The presence of earthworms further significantly enhanced protease activity in the soils with both incorporated and mulched maize residues during two cultivation seasons, but only significantly increased alkaline phosphatase activity in the soil with incorporated maize residue during the rice cultivation season. Invertase activity was significantly enhanced by the presence of earthworms in the soil with maize residue incorporation during two cultivation seasons. There were no changes in dehydrogenase activity when earthworms were present. Additionally, the five enzyme activities in earthworm casts were significant higher than those in the surrounding soil, especially dehydrogenase and invertase activities. Whatever the treatment, the values obtained for the enzyme activities in both soil and casts, except for dehydrogenase activity in earthworm casts, were significantly higher under wheat than those in rice-cultivated soil. These results indicate that the presence of earthworms strongly affected soil enzyme activities, depending on the method of organic residue application, and the enhanced enzyme activities of earthworm casts probably contributed to the surrounding soil enzyme activities. [Copyright &y& Elsevier]