Straw production potential for biofuel generation by grain crops in the Pampas

H.S. STEINBACH, R. ALVAREZ

Conferencia; 19th ISTRO Conference; 2012

Crop residue is an alternative for biofuel generation but it use determines a lower carbon input to the soil and a higher nutrient extraction from the agroecosystem. Our objectives were to estimate: 1) straw production by common pampean rotations and their energy equivalence, and 2) nitrogen extraction by residue harvest. The Pampean Region was divided into six subregions according to geomorphological, climate and soil differences, and historic statistics at county level were used for estimating common rotations and crop yield for the 2006-2010 period. Using results from 130 local field experiments we calculate average grain/shoot ratio and nitrogen content of post harvest straw. An efficiency of 20 % was assumed for straw harvest and biomass conversion to energy was performed. The energy cost of returning the nitrogen harvested in residues was also assessed. Main pampean crops are soybean (Glicine max), wheat (Triticum aestivum), corn (Zea maiz) and sunflower (Helianthus annus). Soybean is the principal crop accounting for 37 to 73% of cultivated surface depending on the subregion. Straw production and nitrogen extraction by residue harvest varied in the order corn>wheat>sunflower>soybean. In the humid and the semiarid portions of the Pampas harvested straw is 3.8 and 2.4 t DM ha-1 yr-1 respectively. Nitrogen harvested in residues varied from 20 kg ha-1 to 13 kg ha-1. Transforming the whole pampean harvested biomass production into energy (1.11 EJ yr-1) it is equivalent to ca. 200 Mbarrels yr-1 fosil fuel. The cost of returning harvested nitrogen is round 2 % of the harvested energy.