Abstract
Biodiverse legume-rich pastures (BLRP) have been recommended for extensive animal production since they can improve productivity and pasture quality. However, the consequences for the N balance within the agro-system, due to the increase in biological N 2 fixation, must be monitored. A field trial was carried out to evaluate the soil N availability in a BLRP in comparison with an adjacent unsown pasture. The field experiment consisted of growing tufts of nitrophilic species (turnip, Brassica campestris and rye, Secale cereale) in the pastures rounded by PVC rings. Soil inorganic-N levels were monitored during a period of one year. The potentially available soil N was determined by growing ryegrass (Lolium multiflorum) in a pot experiment and carrying out several chemical extraction methods. The mean values of N recovered by field-grown turnip and rye were, respectively, 30.6 and 31.1 kg ha–1 in BLRP, not statistically higher than that recovered in the unsown pasture. This is consistent with the very low levels of soil inorganic-N observed both in BLRP and the unsown pasture. Nitrogen recovered by ryegrass grown in pots was significantly higher in the soil collected from the BLRP than in soil from the unsown pasture. In this study, plant-available inorganic-N appeared as a strong limiting factor for the growth of the non-legume component. The BLRP seems to be currently environmentally sound, since the risk of N loss is practically non-existent. However, the potentially mineralisable organic N is increasing, which requires a further monitoring of the soil N dynamic as the pasture ages.
Highlights
The fertility of soils in most of the Portuguese territory is low, f irstly limited by soil shallowness
The field experiment consisted of growing tufts of nitrophilic species in the pastures rounded by PVC rings
The mean values of N recovered by field-grown turnip and rye were, respectively, 30.6 and 31.1 kg ha–1 in Biodiverse legume-rich pastures (BLRP), not statistically higher than that recovered in the unsown pasture
Summary
The fertility of soils in most of the Portuguese territory is low, f irstly limited by soil shallowness. The abundance of steep slopes in the landscape encourages soil erosion which counteracts pedogenesis, the process of soil formation. Extensive animal production is one of the most interesting possibilities of land use. Since native pastures are poor in terms of productivity and pasture quality, some farmers have increased the productivity of their lands by sowing subterranean clover-based pastures. In the last few years, biodiverse legume-rich pastures (BLRP) have been recommended to the farmers by Fertiprado, the biggest seed company in the country. It is expected that these multispecies and multi-varietal pastures will show high environmental plasticity, with each species exploiting different ecological micro-niches, increasing the productivity, the inter-annual production stability and the longevity of the pasture
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