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Effect of Weed Management on the Leaching Loss of Nitrogen in Lipa Clay Soil
Thesis Abstract:
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 croppings. The first cropping was grown from 23 November 1979 to 18 January 1980 while the second crop was grown from 25 February to 13 April 1980.
Effects of seed clippings on the leaching loss of N in the first cropping was not significant. However, around 41 mgm N/pot was conserved through weed clipping. Unclipped or undisturbed weeds significantly reduced leaching loss and about 91 mgm N/pot was conserved.
The 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 undistributed significantly reduced leaching loss. The result of the first cropping showed that N from ammonium sulfate was more easily leached than N from urea. Only about six 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 N was obtained between ammonium sulfate and urea as sources. Leaching loss decreased with growth period. An inverse relationship between the amount of N leaching from both sources and growth period (days after planting) of crops was observed in the second cropping. The 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 weeds in the first cropping was significantly higher when urea was used. The result of the second cropping was different from the previous one as higher N uptake by corn and weeds was obtained when ammonium sulfate instead of urea was used as N source. Nitrogen uptake by corn was significantly reduced when weeds (R. exaltata) were allowed to grow undistributed. About 26 percent reduction of N uptake by corn was observed in the first cropping and around 50 percent N uptake reduction was obtained in the second cropping. Weed clipping significantly reduced N uptake in the second cropping but not in the first cropping.