PURE AND MIXED PERENNIAL BIOMASS CROPS FOR A CONSTRAINT MARGINAL LAND IN NORTH-CENTRAL SPAIN (A 6-YEAR STUDY)

Growing energy crops in marginal lands is frequently encouraged by policy makers to minimize landuse competition with food crops. The term "marginal land" is referred to lands with low economic competitiveness where farm margin of traditional mono-cropping agriculture has been below opportunity costs. The aim of this study is to evaluate the biomass production and the energy content of different C-3 perennial grasses grown on a marginal Spanish area under rain-fed conditions. Yields of pure and mixed C-3 grasses were evaluated in a 6-year study utilizing traditional farming techniques. Productivity ranged 2.6-4.4 Mg DM.ha(-1).y(-1), being tall wheatgrass cultivar Alkar the one that yielded the highest productivity. Pure tall wheatgrasses (var. Alkar, Jose and generic) as well as tall wheatgrasses mixed with rye or tall fescue clearly showed higher productivity than that achieved with siberian wheatgrass, crested wheatgrass, or mixtures of tall wheatgrass with sweet clover. Over a range of 6 years, the energy content provided by crops of tall wheatgrasses (89 GJ ha(-1).y(-1)) was 38% higher compared to than the energy content of siberian and crested wheatgrasses (58 GJ ha(-1).y(-1)).