LAUSR

935 Green manure is a crop residue that releases N for subsequent cash crops such as vegetables, potato (Solanum tuberosum L.), cereals, and oilseeds (ThorupKristensen, 1993; Vyn et al., 2000; Entz et al., 2001; Sincik et al., 2008). On average, the N released from green manure provides 17% of the crop N requirements during the growing season (Gardner and Drinkwater, 2009) improve the N recovery use efficiency from green manure, it is important to know how much mineral N (NH4 + plus NO3 –concentrations) will be released from the residues, when net N mineralization occurs after the plow-down event, and how much mineral N is acquired assimilated by the subsequent crop. This can be evaluated in laboratoryand greenhouse-based studies on plant N uptake, or through non-plant testing methods. Methods to predict the amount of organic N mineralization after the incorporation of green manure residues often rely on analysis of mineral N in field soil cores through soil chemical extraction with 2 M KCl or 0.5 M K2SO4 solution. The disadvantage of soil chemical extraction is that removal of soil cores disrupts the sampling area, demands more time, and does not always reflects the nutrient release dynamic because cores are collected at discrete point in time. In contrast, IEM can be deployed in situ, their two-dimensional nature allows a better contact with the soil matrix and causes minimal soil disturbance, and act as a sink for NH4 + and NO3 – ions, similar to plant roots, while showing similar responses to the environmental conditions and edaphic factors that affect plant N uptake (Qian and Schoenau, 2002; Zebarth et al., 2009). This was by León Castro and Whalen (2016a), who showed that the concentration of IEM-NO3 ––N was sensitive to arugula N uptake and ambient variables (i.e., rainfall, soil temperature, and soil moisture) in a field planted with green manure, before and after the green manure plow-down occurred. The reliability of IEM as an indicator of N release can be validated by correlating mineral N concentration, IEM-NH4 +–N and IEMNO3 ––N values during crop residue decomposition. Nitrogen Supply from Green Manure Enhanced with Increased Tillage Frequency: A Note