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- Effects of Cropping History on Soil Erodibility of Kaingin Farms in...
Effects of Cropping History on Soil Erodibility of Kaingin Farms in Mt. Makiling, Laguna, Philippines
Thesis Abstract:
Erosion is a major problem of kaingin farming, The study aimed to better understand the soil and other characteristics of kaingin areas of different cropping ages that affect erodibility. In the process, two other objectives were achieved: establishment of the relationship between kaingin land use and soil erodibility and assessment of the effectiveness of the raindrop impact technique in determining soil erodibility.
Erosion plots were established at the slopes of 36 percent, 50 percent, and 70 percent gradients of the secondary forest (zero age cropping), new kaingin (three-year-old cropping), and old kaingin (five-year-old cropping) areas. Runoff and sediment load were monitored in relation to various soil properties, vegetation cover, and climatic factors. Soil samples were collected for testing with the raindrop impact technique.
Results of the investigation showed that the significance of cropping age on erosion depended primarily on vegetation cover and organic matter. There was a sharp decline in organic matter from the secondary forest to the new and old kaingins. A leveling trend, however, was observed in the new and the old kaingins. This was attributed to the kaingineros' ability to shift their cropping and cultural practices to those that could maintain the soil organic matter level. Consequently, the resulting erosion from the new and old kaingins did not differ much.
Analysis of the data showed the primary importance of vegetation cover and organic matter in protecting the soil against erosion. In the raindrop impact technique determination of soil erodibility, organic matter was found to be the most important strengthening factor against breakage even under wet conditions where the soil peds were much weaker than those under either air-dried or oven-dried conditions.
The other soil characterisitcs such as bulk density, percent porosity, percent sand, percent silt, and percent clay did not show definite trends in relation to different cropping ages. Though showing interactive relationships with each other and with organic matter, these factors, when taken individually, did not significantly influence erosion with the exception of soil texture in some cases.
The dynamics of runoff was shown to be different from that of sediment load with runoff influenced more by climatic factors while sediment load, more by soil factors. Total rainfall, rainfall intensity, and wind velocity was the only significant climatic factor. Sediment load, however, was strongly influenced by runoff.
The general trend of soil erodibility at various cropping ages as determined by the raindrop impact technique showed similarity to that determined by actual field monitoring using erosion plot. The difference was attributed to some inherent weaknesses of the raindrop impact technique such as its inability to account for effects of factors such as vegetation cover and slope and variability due to effects of ped size and shape.