Nutrient and trace element budgets of fields in organic farming– examples from Austria

Abstract 

In organic farming, the C and N budget in the soil can be improved by growing clover grass to increase the levels of humus and nitrogen soil content. Other elements may be supplied through organic fertilization as well as the recycling of straw and organic waste. Three case studies attempting to close nutritional cycles on site are presented, to avoid input of external fertilizers. The first case study examined an inter-farm exchange of organically grown clover grass for conventional cattle manure and organic cattle slurry of about equal total nitrogen contents. In this cooperation the farm providing the clover grass lost K, while receiving a surplus of all other elements analyzed (Ba, Ca, Cu, Li, Mg, Mn, Na, P, Sr, Zn). In the second case study, input of cattle slurry versus output of barley grains and straw was examined. Cattle slurry containing about equal amounts of N, K and P found in summer barley grains plus straw per hectare was applied, increasing Ba, Cu, Li, Mg, Mn, Na, Sr, and V on site, whereas Ca and Mo decreased. At half the concentration of slurry, in addition to Ca and Mo, the levels of Ba, Cu, K and Mg decreased as well. If straw was left on the field, all of the elements investigated increased. The third case study analyzed the fertilization effect of digestate from alfalfa-based biogas production on a non-legume cover crop mixture followed by summer barley. Fertilization with liquid digestate led to higher amounts of dry matter and higher contents of Ca, K, Na, P and Sr in cover crop biomass per hectare but had no effect on the yields of the following summer barley. Analysis of soil nitrate before, during and after the cover crop period showed no signs of nitrate leaching. Therefore, the fertilizer N could successfully be stored in plant biomass over the critical winter period for the following crop. 
The three case studies show that innovative methods of clover grass use can successfully close nutrient cycles on stockless organic farms so they can subsist without a need for external supplies.