Nitrate and ammonium losses from surface-applied organic and inorganic fertilizers

SUMMARY Animal manures are a valuable resource, providing readily available plant nutrients; however, runoff from lands receiving animal manure has been shown to contribute to water pollution. Understanding the loss of nutrients from slow release fertilizers, such as animal manure, after application is critical in determining and designing practices to reduce and/or control the temporal availability and potential offsite transport of NO 3 -N and NH 4 -N after application. A block study was designed to compare and contrast the temporal losses of NO 3 -N and NH 4 -N from three slow release fertilizers (sulphur-coated urea, composted dairy manure, and poultry litter) and one fast release fertilizer (ammonium nitrate) applied to bermudagrass ( Cynodon dactylon L. Pers.) turf. Cumulative NO 3 -N loss from plots receiving application of the manufactured (NH 4 NO 3 and sulphur-coated urea) products was significantly ( P <0·05) greater than the measured losses from plots receiving application of natural products (composted dairy manure and poultry litter). The cumulative NO 3 -N recovered in the runoff expressed as a proportion of applied N was 0·37 for ammonium nitrate, 0·25 for sulphur-coated urea, 0·10 for composted dairy manure, and 0·07 for poultry litter during the 10-week study period. Cumulative NH 4 -N recovery fractions were an order of magnitude less than the cumulative NO 3 -N fractions and no significant differences ( P >0·05) were measured across treatments. Significant differences ( P <0·05) in NH 4 -N and NO 3 -N loss through time were measured for the four treatments. The findings of the present study indicate that land-applied animal manures are less susceptible to initial losses of N when compared to manufactured fertilizers.