ABSTRACT
Summary The experiment was designed to determine the effects of land spreading of animal manures on the nutrient content of surface runoff water and infiltrating soil water. This report deals only with nitrogen (N) and attempts to quantify the losses through runoff, leaching, and volatilization of ammonia (NH3) as well as N uptake in the grass over a 3-year period. Experimental plots sited on grassland, on two soil types (a moderately drained loam and an impermeable gley), were equipped to collect surface runoff water. Ceramic probes were installed in each plot at 15-, 30-, 60-, and 100-cm depths to extract infiltrating soil water. Pig slurry was applied at three different rates three times each year. Inorganic fertilizer and control plots were included. Volatilization of NH3 and nitrification were determined by daily analyses of soils following slurry application. Grass was harvested three times each year. The results indicate that 40%-80% of the slurry ammonium nitrogen (NH4 + - N) was lost through volatilization of NH3 within ~ 7 days of application. In the moderately drained soil, nitrification of the remaining N occurred as shown both by soil analyses and by subsequent appearance of nitrate nitrogen (NO3 - - N) in the soil water. The leaching losses increased as rate of slurry application increased and were estimated to account for ~ 5 % of the total applied N at the lowest rate of slurry application and ~ 13% at the highest rate. Leaching losses from fertilizer were comparatively higher than from slurry. At the impermeable site NO3 - - N was absent from the soil water of slurry treatments during the first 2 years of the experiment. It was not clear whether nitrification was inhibited in the waterlogged soil, but there was evidence to suggest that nitrification in the top few centimeters of soil may have been followed by rapid denitrification in the anaerobic subsurface soil. Rainstorms causing runoff did not occur for several weeks following most of the treatment application dates, and therefore losses in runoff were small. The highest recorded loss was ~ 8 % of the (NH4 + - N) applied when rainstorms occurred soon after application at the impermeable site in November 1978.
348Nitrogen uptake in grass from slurry was very poor, ranging from 20% to 24% recovery from the low rate to 14% to 17% from the high rate. Uptake from fertilizer was 52%-55% in the same period. The results show clearly that spreading animal slurry on grass is a very inefficient method of recycling its nitrogen content. Improved efficiency would depend on alternative methods of land spreading, such as injection, where losses through volatilization of NH3 would be greatly reduced.
