MINERALIZATION AND PLANT AVAILABILITY OF NITROGEN IN SEAFOOD WASTE COMPOSTS IN SOIL

Nitrogen availability to plants from seafood waste composts must be de termined for composting to be adopted as a means of seafood waste disp osal and for utilization of the compost, In a a-year study, the availa bility of N to silage corn in the year of application and the residual availability in the following year were evaluated under field conditi ons for four composts made from sawdust and seafood wastes, A broad ra nge of compost rates was used to facilitate the study of the residual N availability, The composts were: HGF (groundfish waste with hemlock/ fir sawdust); AGF (groundfish waste with alder sawdust); HCS (chitin s ludge with hemlock/fir sawdust); and ACS (chitin sludge with alder saw dust), In the composts made with alder sawdust, the fraction of total N that was in inorganic form was smaller than that in the composts mad e with a hemlock/fir sawdust mixture, In the year of compost applicati on, corn yields and N uptake were affected by the type of compost and rate of compost addition, and the rate effect varied with the compost type, The amount of inorganic N added in the composts was better than the organic N or C:N ratios of the composts at predicting corn yields and N uptake in the year of compost application. None of these compost -related characteristics was closely correlated with residual N availa bility in the next year. The soil inorganic N concentration, which ref lects the overall effect of composts and environmental conditions on N transformation, accounted for most of the variability in corn yield a nd N uptake during the a-year period, Although the mineralization pote ntial of the organic N fraction in the HGF was low in a laboratory inc ubation, a sizable reduction of total N and organic C concentrations i n the soils amended with this or other composts under field conditions suggests that considerable mineralization during the subsequent year occurred in this region, which is characterized by mild temperatures a nd high rainfall in the winter, Because of the limited residual N avai lability of the HGF, AGF, or HCS, annual addition of the composts at l ow rates sufficient to sustain the soil productivity is more appropria te than less frequent addition at high rates.