Soil loss and surface runoff from farmland under coffee trees with different weed managements were investigated in Lampung, South Sumatra, Indonesia during rainy seasons from 1996 to 1999. Three treatment practices investigated were as follows : coffee without cover crop ; coffee with Paspalum conjugatum sp. as cover crop, and coffee with natural weeds. Weed management was done every two week by clearing all the weeds in coffee plot, and cutting the weeds around the coffee trees with diameter 1 m for the weedy plots. The results showed that the maximum daily rainfall and intensity based on 10 minutes observation were 82 mm/day and 120mm/h, however, only 14.2% of rainfall intensities was greater than 25 mm/h (classified as erosive rainfall intensity). A relationship between erosivity index (R) and daily rainfall(X) was found as follows : R =1.624 (X-10.9), where R : daily erosivity index (m2-t/ha/h) and X : daily rainfall (mm/day). The runoff ratio for clean-weeded coffee ranged from 7.0 to 15.9%, and decreased after the second year because of the coffee canopy growth. The presence of Paspalum conjugatum had reduced runoff until zero after the third year, whereas in natural weeds plot, runoff became zero after the fourth year. The highest soil loss was found in clean-weeded coffee which reached 22.7 t/ha in the second year of experiment. The use of cover crop could suppress soil loss until zero after the third year in Paspalum plot and after the fourth year in natural weeds plot. However the good management of weeds as cover crops is necessary due to the bad performance of coffee growth at both weedy plots. The average soil loss from clean-weeded coffee plot was 1.24 mm per year which was below the soil formation rate in Indonesia.
In acid sulfate soils, the material which causes heavy acidity is sulfate ; mainly pyrite (FeS2), produced from the sediments in the sea that contain a lot of organic matter and sulphuric acid and subjected to heavy reductive conditions. In the process of sulphuric acid production, particularly in the primary acidity stage, chemical acidity and bacterial acidity act together. These bacteria (Thiobacillus ferrooxidans and Thiobacillus thiooxidans) contribute a major role as catalysts. The purpose of this study is to investigate the relationship between the acidification process and the temperature and water content conditions through an incubation experimentation. Results are listed as follows :
(i) In 10-50°C temperature conditions, the soil was acidified more strongly at high temperature by chemical oxidation accompanied by high evaporation rate. The acidification was stopped when the quantity of evaporation became lower than the level of soil moisture.
(ii) When keeping the water condition with almost no evaporation, the speed of acidification is slow but continuous. At 30°C and at around —31.0 kPa, the acidity is extremely strong. The above results show that the speed of evaporation influences the acidification process and microstructure of the soil matrix. Drying is also an important factor that influences acidity due to bacterial activity.
Sediments transported from various land uses and entrapped by natural vegetative filter were measured from January to November 1999 in a hilly humid tropical area of Lampung, South Sumatra, Indonesia. A very simple sediment trap made from a PVC pipe with diameter of 10.9 cm was designed for measuring the sediment yield. Five types of land uses were chosen as follows : (a) coffee garden in multistrata system followed by rain-fed agriculture and grass filter, (b)mixed-coffee garden followed by short shrub filter, (c) clean-weeded coffee garden followed by long shrub filter, (d) clean-weeded coffee garden, and (e) secondary forest followed by new forest remnant. The measurement during eleven months showed that the mixed-coffee garden produced the highest sediment yield (719.7g/m2), and the lowest sediment yield was derived from secondary forest area (0.08g/m2). The sediment yield from clean-weeded coffee system was around 93.4-279.7 g/m2, and multistrata system indicated a low sediment yield (2.3 g/m2). Although mixed-coffee garden showed a very high yield of sediment, natural vegetative strips entrapped 99.7% of the sediment. The vegetative filter zone covered with grass (1.5 m long) and short shrubs (3 m in length) could entrap 93.5% and 99.7% of sediment respectively, and the long shrub filter (12 m in length) could entrap only 52.5% of the sediment due to the concentrated flow in the longer slope. The surface cover condition of the land use system and farming activities (weeding, tillage, fertilizer application) indicated a high contribution on sediment yield than the other erosion factor.
Effects of different initial moisture conditions on the formation of wetted soil volume under micro-irrigation were investigated in a layered soil having a plow layer and a subsoil layer with macropores. Water was applied at a constant rate of 100 cm3 min1 for 720 minutes using a perforated tube covered with vinyl mulch. Water application efficiency was also evaluated from soil water storage and infiltration loss caused by bypass flow. In the case of initially dry condition, the wetting front was spread in an elliptical shape with the major axis in the downward direction. In the case of wet condition, however, the horizontal boundary between the plow layer having high saturated hydraulic conductivity and the subsoil layer having low one affected infiltration. Water reached to the boundary flowed horizontally and infiltrated into the plow layer from the bottom. The amount of water infiltrated vertically was more than that of horizontally infiltration in an imaginary main root zone. Infiltration loss beyond the root zone due to bypass flow was accounted for 89% in dry condition and 75% in wet condition for 720 min respectively. After 70 min irrigation, the rate of storage was unchanged in both the dry and the wet conditions. In view of water application efficiency, irrigation period exceeding about 70 minutes is inadequate.
In acid sulfate soils, the heavy acidity is caused by the oxidation of sulfate, mainly pyrite (FeS2). In the primal acidify stage chemical and bacterial acidify work together. These bacteria (Thiobacillus ferrooxidans, Thiobacillus thiooxidans) have a huge role as a catalyst. This studies were examined the effects of drying on bacterial acidification, mainly on Thiobacillus ferrooxidans, and the formation of iron in the soil by the incubate experimentation. Five water content stages were set (1.30〜0.25kg/kg) by drying process in the incubator at 30°C for water adjustment. After the treatment, these samples were contained in the each bottles and started to culture at 30°C. Thiobacillus ferrooxidans propagated rapidly in the water content of Liquid Limit (LL)〜Plastic Limit (PL). Near the water content of PL, the propagation of the bacteria became slow, and they became decline near by the water content of Shrinkage Limit (SL). Amorphous - free - iron increased at the primal of acidification and changed for crystallized - free - iron. Around SL, the water content that the soil pH was stable, the propagation of the bacteria became slow, and the formation of iron became stable. In the range of water content 1.00〜0.70kg/kg (LL〜PL), the samples acidified strongly.