Effect of varietal and species diversity on nitrogen fixation and nitrogen cycling in an organic faba bean spring wheat intercropping system

University essay from SLU/Department of Work Science, Business Economics, and Environmental Psychology

Abstract: This study was undertaken to evaluate the effect of varietal and species diversity of faba bean and spring wheat on N2 fixation and N cycling in an organic system. The field experiment was carried out at SLU Alnarp to quantify biological N2 fixation using 15N natural abundance method. The measurements were taken at two physiological stages of faba bean, at pod filling and at full maturity. In general N2 fixation, shoot N yield and soil N uptake increased at maturity while the proportion of N derived from fixation, %Ndfa and biomass yield decreased. No significant effect of diversity was found on N2 fixation but significant effect of diversity on %Ndfa was recorded at full maturity. Significantly positive correlation was found between the amount of N2 fixed and biomass yield, %Ndfa and N concentration. Soil N uptake positively correlated with shoot N yield but negatively with N2 fixation. The calculated biomass yield and N2 fixation per sown faba bean plant showed the increased advantage of varietal mixture and intercropping. The advantages also occurred in residual Nitrogen, Crop Harvest Index, Nitrogen Harvest Index, Nitrogen Balance and Nitrogen Utilization Efficiency. Significantly higher Nitrogen Utilization Efficiency was found in mixture of Alexia, Gloria and Wheat. Highest N balance was found in mixture of Alexia and Gloria. Crop Harvest Index was highest in mixture of faba bean varieties with spring wheat but the growth and development of wheat was highly suppressed in the mixture. The potential application of the study outcomes in practical farming situations was estimated by a questionnaire study with structural and semi structural questions. The questionnaire was sent to advisors working within the organization “Greppa Näringen” (Focus on Nutrients) program to increase farmers‟ awareness about agricultures‟ potential impact on climate change. The interest among responding advisors (13 out of 35 who received the questionnaire) on crop diversification was high. The diversity in cropping system including faba bean was perceived important by a majority of the advisors mainly for developing crop rotation that decrease the need to buy animal feed and industrial N. Marketing, harvesting and susceptibility to drought were the main concerns associated with diversification of faba bean crops. Based on the results from the empirical study and questionnaires I can conclude that diversification of cropping systems is a very important strategy from both environmental and agronomic aspects.

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