Eficiencia de uso del Nitrógeno por forrajeras abonadas con estiércol de bovinos lecheros en la región Pampeana, Argentina

Intensification of animal production systems, and therefore the increase in livestock stocking rate, increases the amount of excreta that can be used as a nutrient source for forages crops. The purpose of this study was to compile and compare a) effluent quality results from different dairy production areas of Argentina and b) results from studies carried out in two different environments, on nitrogen (N) use efficiency of dairy cattle manure used as fertilizer of forage and grain crops. Analytical information of 36 manure samples from stocking piles or solid separator treatments in the different regions (dry matter (%DM), nitrogen (%N), and phosphorus (%P)) was systematized by using the same sampling methods in the North of Buenos Aires (BA) and Center of Santa Fe (SF). Information was compiled regarding soil, weather conditions, manure quality, doses and application strategies, and productivity of 13 studies, five studies carried out in BA and eight in SF. The forages and crops were: alfalfa, oats, corn, Hungarian millet, annual ryegrass, polyphitic pastures, sorghum for both grazing and silage, and wheat. In order to compare results, the N Use Efficiency indicators were used, both for total N (EUN) as for plant available N (EN-NDP),in relation to the control treatment. It was expressed as kg DM·(kg applied N or NDP)-1. NDP is obtained with international information to estimate the expected mineralization, a priori, during the year of application. Manure quality presented variable characteristics in both zones (%DM from 16.3 to 56.0, %N from 2,9 to 19, and %P from 0.1 to 0.8). These are in accordance with international studies, and attributed to different water management practices, type of manure, solid separation technique, and diet components. Values for EUN varied from 2,3 to 51,8 kg DM.Kg N-1, varying from crop and soil and weather conditions. Temperature and rainfall variables had a greater incidence on EUN, over soil and manure variables, such as prior management, moment and division of the applied total dose. That is to say, with moderate temperatures and adequate moisture, better mineralization conditions are expected which in turn increase EUN of these organic nutrient resources. These sources require very specific conditions for their nutrients to become available for crops. In the different areas of the Pampa Region, cattle manure could be used as a nitrogen source, improving aerial biomass accumulation by its reuse.