Abstract
Certain farms in Japan, namely unfertilised farms (UFs), have been able to maintain high productivity for over 40 years without applying fertilisers or composts. This study aimed to characterise the physicochemical, biological and micromorphological properties of soil in UFs compared with control farms in Eniwa and Nariita and to identify characteristics that are associated with crop productivity. In UFs, no plough pan was observed. The thickness of the effective soil depth (ESD) of UFs was greater than that of CFs. The concentrations of soil organic carbon, total nitrogen and nitrate-nitrogen in ESD of UFs were higher than those in ESD of CFs. Soil microstructure observations indicated the strong development of a granular microstructure with large amounts of void space and a high fractal dimension in both surface and subsoil horizons of UFs. Dry yield had a strong correlation with ESD thickness and fractal dimension of voids. Thus, the management of unfertilised cultivation promoted the development of soil aggregation in both A and B horizons. The increase in ESD, soil pore spaces and complexity with the development of subsoil structure improved the productivity of unfertilised cultivation.
Highlights
Problems such as groundwater and river nitrogen pollution have occurred in Japan (Hojito et al 2003; Kumazawa 1999; Yamaki et al 2013), and sustainable low-intensity agriculture is attracting increasing attention (Mander 1999)
According to the World Reference Base for Soil Resources (WRB; IUSS Working Group 2014), E-unfertilised farms (UFs) and E-control farms (CFs) are classified as vitric andosols and N-UF and N-CF are classified as silandic andosols (Table 1)
Our results show that UFs have very thick effective soil depth (ESD)
Summary
Problems such as groundwater and river nitrogen pollution have occurred in Japan (Hojito et al 2003; Kumazawa 1999; Yamaki et al 2013), and sustainable low-intensity agriculture is attracting increasing attention (Mander 1999). The specific method is as follows: (1) no agricultural chemicals, fertilisers or manures (nitrogen, phosphorus or potassium fertilisers, composts, animal manure, minerals, etc.) are applied; (2) in-house seeds are used; (3) continuous cropping of the same crop is maintained; (4) the soil surface is covered to a depth of approximately 1 cm with mulch, which incorporated to a depth of approximately 10 cm using a rotary tiller after harvesting and (5) weeding is Nakatsuka and Tamura SpringerPlus (2016)5:283 done two or three times per year (Ishii 2010; Oda and Hosen 2011). A study of the effect of soil characteristics on productivity in those farms may give pointers for increasing crop productivity in lowinput agriculture
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