Accelerated phosphorus accumulation and acidification of soils under plastic greenhouse condition in four representative organic vegetable cultivation sites

Organic vegetable cultivation under plastic greenhouse conditions is expanding rapidly in the suburb of big cities in China due to the increasing demand for organic, out-of-season green vegetables and the sustainable development of agriculture. Phosphorus (P) is not only an important plant nutrient, but also a major contaminant in the water environment. However, information on the accumulation and distribution of P in organic vegetable soils under plastic greenhouse conditions is limited, relative to the open cultivation systems. Therefore, twenty-six plastic greenhouse vegetable soils (PGVS) were selected randomly from four representative organic vegetable cultivation sites located in the suburb of Nanjing, China. For comparison, 15 open vegetable soils (OVS) near the PGVS with similar soil and cultivation practices were selected. Soil pH, organic matter (OM) and the various P accumulation characteristics were investigated. We found that soil pH in PGVS were significantly decreased by 0.57-1.17 unit with obvious signs of acidification, compared with that in OVS. Soil OM was different for different sampling locations, but in general it was higher in PGVS than OVS. Soil total P (TP), inorganic P (Pi) and Olsen-P of PGVS were higher than those in the OVS. Olsen-P of all soil samples were far above the recommended optimum value of 20 mgkg(-1) for field crops, and over 60% soil samples were considered excessive (>150 mg kg(-1)) in the PGVS and OVS. There were significant correlations between total P, available P and soil pH in those vegetable soils. Al-P/Fe-P ratio was also significantly correlated with vegetable soil pH (Y-pH = 7.44-1.32 XAl-P/Fe-P, r = -0.705, p < 0.01). Soil total P-i was negatively correlated with soil pH in vegetable soils (r = -0.328, p < 0.05), but the interactive effect of soil various P-i and soil pH need to be further investigated through a series of controlled tests. Our results suggest that the rapid P accumulation and acidification make the current plastic greenhouse vegetable production in the study area unsustainable and better organic manure management practices need to be implemented to sustain crop yields while minimizing the impact of vegetable production on the environment. (C) 2015 Elsevier B.V. All rights reserved.