Growth of tall fescue in compost/fertilizer blends

Composts are considered low-analysis fertilizers because their N and P content is from 1 to 2% and the N mineralization rate is near 10%. If compost is added to agricultural land at the N requirement of grain crops (40 to 100 kg ha), application rates approach 40 to 100 mt ha. Much lower rates may be advisable to avoid accumulation of constituents such as heavy metals found in some composts. Combining low-amendment rates of composts with sufficient fertilizer to meet crop requirements is an appealing alternative which (i) utilizes composts at lower rates than those needed to supply all of the crop N requirement, (ii) reduces the amount of inorganic fertilizer applied to soils, and (iii) reduces the accumulation of nonnutrient compost constituents in soils. A study was conducted to compare the effects of blends of biosolids compost (C) with urea (U) or NH4NO3(N) fertilizers with fertilizer alone on tall fescue (Festuca arundinacea L.) growth and N uptake. Blends that provided 0, 16.7, 33, or 50% of the 100 mg N kg application rate as compost N and 100, 83.3, 67, or 50% as fertilizer N were added to Sassafras soil (Typic Hapludults). Fescue was grown on the blends in a growth chamber for 109 days. Fescue yields decreased linearly with decreasing fertilizer level for both NH4NO3 and urea and with or without compost. Nitrogen uptake by fescue was different for fertilizer- than for compost-amended pots, depending on the rate of fertilizer added. Paired comparisons based on cumulative 109-day data indicated yields from NC67 (67% NH4NO3-N, 33% compost N) and NC83 equaled the yield of N100. Similarly for blends containing urea, UC67 yield was equal to U100. Nitrogen uptake from NC83 was equal to N100, but N uptake from NC67 was significantly less than from N100. Nitrogen uptake by UC67 was significantly less than U83 which had a greater mean N uptake than N100. The data suggest that compost N can replace one-third of the fertilizer N required by fescue without decreasing yield. Because the mineral N plus the mineralization of organic N that comprises the compost N portion of the blends did not equal that of the corresponding fertilizer alone, constituents other than N contributed to yields from the compost fertilizer blends.