This thesis presents the results of field experiments on soil, water and nutrient conservation and measurement. The main objective of this research was to identify suitable technology to minimise soil loss and improve soil fertility in farmers' fields involving local knowledge and farmers' participation in the research. The experiments were conducted at different agro-ecological sites in the middle hills of Nepal.
Nayatola was selected, a representative site for sloping land cultivation system and low to medium rainfall in the middle hills. The altitude of the area in which experiments were conducted is ranged from 11 00 to 1400 m asl and annual rainfall is 800-1400 mm.
Farmers have adopted a maize-based cropping system with farmyard manure application and a small area of ginger with mulching practice as a cash crop in sloping bari lands. Landruk was selected, a representative site for bench terracing system and high rainfall.
Experiments were conducted at the altitude ranging from 1400-1600 m asl where maize/millet and maize/wheat or barley are main cropping systems receiving 3000-3600 mm annual rainfall. Bandipur was another site selected, a representative for citrus growing pocket areas. This site receives 1000-2000 mm annual rainfall and having bench terracing system with maize and upland rice based cropping systems and citrus orchards. The altitude of experimental site is ranged from 900 to 1100 m asl.
Results indicate that a low proportion of rainwater flows into runoff compared with infiltration in the soil in all sites. However, some erosive rainfall events occurred during the early season resulting in heavy soil loss.
Ginger strip with mulch alternating with maize strips across the slope reduced soil loss from 144 - 1756 kg/ha/yr to 58 - 281 kg/ha/yr in the maize-based cropping system on the sloping bari lands at Nayatola. A legume crop such as soybean in strips alternating with maize strips also reduces soil loss from 867-1756 kg/ha to 555-865 kg/ha and improved soil fertility in the bari lands.
Run-on diversion reduced soil loss from 886 - 7256 kg/ha/yr to 4 78 - 4653 kg/ha/yr from bench terraces under high rainfall conditions at Landruk. Grass planted in terrace risers can also reduce soil loss from cultivated terraces once roots have been established. Setaria aneps is a suitable species for cultivation in terrace risers in Landruk and Bandipur areas.
However, it requires 2-3 years for establishment in risers and repeated planting in the early years. Native grass species dominated for the first few years. After three years Setaria covered whole risers, produced more grass and minimised soil loss compared to risers dominated by native grasses. The planting operation accelerated soil erosion during the first two years.
The narrow-terraced maize-based system is more sensitive to soil erosion compared to the wide-terraced maize-based system. The narrow-terraced maize-based system lost higher amount of soil (812 - 2804 kg/ha/yr) than the wide-terraced maize-based system (222 - 745 kg/ha/yr) in Bandipur. An intercrop of legume was found to reduce soil erosion in areas of citrus cultivation. Organic carbon is the most important element lost in sediment. 8.5 - 56.9 kg/ha/yr organic carbon was lost in the control plot at Nayatola, 69.6 - 182.1 kg/ha/yr was lost in the control plot at Landruk and a maximum of 14.5 kg/ha/yr organic carbon was lost at Bandipur. These losses were reduced to 1.1 - 15.2 kg/ha/yr with ginger and maize strip cropping at Nayatola and 35.2 - 83.3 kg/ha/yr with run-on diversion at Landruk. Young citrus orchards with an intercrop lost the least organic carbon (3.0 -7.6 kg/ha/yr) at Bandipur.
Total nitrogen lost in sediment ranged from 0.1 - 18.1 kg/ha/yr. Nitrogen loss in sediment was higher at Landruk compared with Nayatola and Bandipur. Available P content was higher in sediments (30-162 mg/kg) than in soils (12-52 mg/kg) at all sites. Sediment loss therefore has an effect on the available P in the soil.
With low soil loss there was less loss of carbon, P and N in the sediment. However, there was a huge amount of NO3-N and K lost in leachate. Strip cropping of ginger and maize and diversion of run-on encourage nutrient loss via leachate. Diversion of run-on minimised soil loss and enhanced water infiltration in the soil. Dissolved N, P and K were not lost
in significant quantities in runoff.
Therefore, strip cropping of maize and ginger with mulch and maize and legume is beneficial to minimise soil and nutrient losses from sloping bari lands in the middle hills.Run-on diversion followed by fast growing grass planting in terrace risers is beneficial to minimise soil and nutrient loss in bench terraced high rainfall areas. lntercropping of legumes in citrus orchard is found the best practice to reduce soil and nutrient losses in Bandipur, a pocket area of citrus cultivation.