Author : Navarro, Alfredo A.

Summary : The effects of weed management on the leaching loss of nitrogen (N) and on the leachability of N from ammonium sulfate and urea as N sources applied to Lipa clay soil which was planted to corn were studied in two croppins. The first crop was grown from 23 November 1979 to 18 January 1980 while the second crop was grown from 26 February to 13 April 1980. Effect of seed clipping on the leaching loss of N in the first cropping was not significant. However, through weed clipping around 41 mgm N/pot was conserved. Unclipped or undisturbed weeds significantly reduced leaching loss and about 91 mgm/pot of nitrogen was conserved. Result of the second cropping echoed the result of the previous cropping. No significant difference was obtained between weed-free and weed-clipped treatment on the leaching loss of N. Weeds undisturbed significantly reduced leaching loss. Result of the first cropping showed that nitrogen from ammonium sulfate was more easily leached than nitrogen from urea. Only about 6 percent of the applied N from urea was leached while around 13 percent was leached from ammonium sulfate. In the second cropping, no significant difference in the leachability of nitrogen was obtained between ammonium sulfate and urea as sources. Leaching loss decreased with growth period. An inverse relationship between the amount of N leached from both sources and growth period (days after planting) of crops was observed in the second cropping. Result of the first cropping did not show this relationship as the trend was disrupted 27 and 30 days after planting due to heavy rainfall. Nitrogen uptake by corn and weeds in the first croppign was significantly higher when urea was used. Result of the second cropping was different from the previous one as higher N uptake by corn and weeds was obtained when ammonium sulfate was used as N source than urea. Nitrogen uptake by corn was significantly reduced when weeds (R. exaltata) were allowed to grow undisturbed.