Efficiency of Compost-Fertilizer Blends Compared With Fertilizer Alone

Combining composts with sufficient fertilizer to meet crop requirements has several benefits over the use of compost as a sole N source, including reduced accumulation in soils of heavy metals, salts, or P. The objective of this research was to find blends of compost and fertilizer that would equal the yield and N uptake of N fertilizer. Biosolids compost-fertilizer blends made to equal 100 mg available N kg−1 were compared with urea or NH4NO3 fertilizer. Zero to 50% of the blend's available N came from biosolids compost; the remainder came from fertilizer. 15N-labeled fertilizer was used to determine the proportion of N uptake attributed to fertilizer. Fescue (Festuca arundinacea Schreb.) was used as the indicator plant. Compost did not increase the efficiency of NH4NO3 fertilizer. The amount of available N provided by urea-compost blends was less than the amount provided by NH4NO3-compost blends. Urea-compost blends that had 17 to 50% fertilizer equivalents from compost equaled 100% urea. Blends of 50% NH4NO3 and 50% biosolids compost available N or 67% NH4NO3 and the equivalent of 33% biosolids compost N produced greater yields and N uptake by fescue. 15N analysis suggested that NH4NO3 fertilizer stimulated soil and/or compost mineralization producing more N than predicted from incubation studies of compost N mineralization rates. However, previous studies showed that soil mineralization was not affected by compost, which leads to the conclusion that fertilizer stimulated compost mineralization. Urea did not affect compost similarly, possibly because of a larger active N pool in urea compost blends compared with NH4NO3 compost blends.