REGULATING FARMING ON SLOPING LAND

Transcription

1 REGULATING FARMING ON SLOPING LAND A PRESENTATION ON THE NEED FOR MANAGEMENT PRACTICES AND SOIL AND WATER CONSERVATION MEASURES AND MISTAKES TO AVOID IN THEIR ADOPTION PREPARED BY THE SUSTAINABLE AGRICULTURAL DEVELOPMENT COMPONENT OF THE UDP 28 FEBRUARY 2006

2 UNSUSTAINABLE LAND USE Photo 1: Excessive rates of soil loss (> 400 t/ha/yr) can be expected from cultivating long slopes of bare soil without SWC measures. A change in land use from corn to perennial crops is advisable ((Brgy Amsipit, Sitio Tahakayo, Maasim, Sarangani)

3 UNSUSTAINABLE LAND USE Photo 2. Natural Vegetative Strips (NVS) and hedgerows cannot control erosion on long steep slopes. This 55%+ slope should have been left under natural forest. It should be planted with a mixture of perennial crops (bananas and fruit trees) to reestablish a multi-storey tree cover. Direct planting of fruit tree seeds followed by field-grafting is a cheap, low risk option

4 UNSUSTAINABLE LAND USE Photo 3: (Photo by Ben Hur Viloria) Growing potatoes on ridges aligned down this very slope will result in massive rates of soil erosion. As the soils get shallower each season there are fewer options for growing other crops, even fruit trees. Eventually the agricultural potential of the farm will be zero. (nr Cablon, Tupi, South Cotabato)

5 UNSUSTAINABLE LAND USE Photo4. Mudslide from cultivating annual crops on very steep slopes. Contour ploughing is only effective on slopes <18% and should be backed up with NVS or hedgerows. This slope needs a permanent tree cover to remain productive.

6 UNSUSTAINABLE LAND USE Photo 5: The end result of inappropriate land use. All this land will produce are land slides and floods (Photos by KRS Proud) Photo 6. Severe moisture stress in young coconut trees growing in soil made shallow by intercropping with maize on steep slopes.

7 UNSUSTAINABLE LAND USE Photo 7. Slopes with rapidly steepening convexity are high susceptible to erosion, and are best left under natural forest cover. Growing of short-term crops should be restricted to the hill tops protected with SWC measures, and the slopes planted with perennial crops from seeds.

8 UNSUSTAINABLE LAND USE Photo 8: Estimated soil losses in excess of 1,500 t/ha/yr are expected from growing cassava on 80% slopes. This is equivalent to a reduction soil depth of 11 cm per year. The soil is only 50 cm deep so there is no future for this farm.

9 UNSUSTAINABLE LAND USE Photo 9: Severe rill erosion on 55% slopes from growing spring onions on unmulched soil. Ploughing removes soil from the base of the hedgerow which intercepts eroded soil from above forming a step. This increases the erosive energy of run-off. A more productive use of this slope is to plant seeds of fruit trees followed by field-grafting of scions.

10 LAND MANAGEMENT TO IMPROVE THE SUSTAINABILITY OF AGRICULTURE ON SLOPES Photo 10: Improved land use. Cross-slope barriers such as Natural Vegetative Strips (NVS) or hedgerows planted on the contour, using an A-frame, can be effective in controlling erosion provided slopes are not too steep or too long and rainfall events are not too high. SALT hedgerows are not effective for SWC on slopes >25% (Brgy Amsipit, Sitio Tahakayo, Maasim, Sarangani)

11 LAND MANAGEMENT TO IMPROVE THE SUSTAINABILITY OF AGRICULTURE ON SLOPES Photo 11: If the seasonal rainfall is not too high, NVS can maintain the productivity of the slopes. Basing the spacing between NVS on soil depth and slope steepness avoids exposing infertile subsoil at the back of the terrace. Better distribution of fertile soil across these terraces would have been achieved if the above terraces were half their current width and the NVS were 2-m wide (not 0.5m). Planting bananas in 2-m wide NVS can increase income. (Brgy Amsipit, Sitio Tahakayo, Maasim, Sarangani)

12 MISTAKES TO AVOID WHEN ADOPTING LAND MANAGEMENT PRACTICES ON SLOPES Photo 12. These uneven terraces resulted from the farmer using the carabao s back method of contouring, as it was quicker and cheaper. Run-off concentrating at the low points will become erosive. Always use an A-frame to determine the contour lines do not trust your eyes! It may take longer but the terraces spread run-off evenly reducing the erosion hazard. (Brgy Maibo, Magsaysay, Davao del Sur)

13 MISTAKES TO AVOID WHEN ADOPTING LAND MANAGEMENT PRACTICES ON SLOPES Photo 13. Hedgerows spaced too far apart for slope and soil depth give more land to cultivate but fertility gradients appear indicating an overall loss in productivity. The stunted growth of cassava over most of the terrace shows the topsoil has moved downhill to the NVS (left side of photo). The land would have been more productive if planted with bananas and fruit trees without any NVS or hedgerows. (Brg Lampitak, Sitio Melina, Tampakan, South Cotabato)

14 MISTAKES TO AVOID WHEN ADOPTING LAND MANAGEMENT PRACTICES ON SLOPES Photo 14: Hedgerows were a good idea BUT putting them in by eye created uneven hedgerows. Ploughing across the slope will channel run-off to the low points forming gullies. Restrict NVS and hedgerows to the upper slopes and hilltops. Planting cassava and sugar cane as hedgerows was not a good idea as they attracted rats. Removing them left partially-formed, unprotected, outwardly-sloping terraces which increases the risk of erosion. Only plants that will remain as permanent features of the landscape (e.g. Vetiver or Napier grass, Rinsonii etc) should be used as hedgerows.

15 MISTAKES TO AVOID WHEN ADOPTING LAND MANAGEMENT PRACTICES ON SLOPES Photo 15. A combination of lemon grass hedgerows, contour cultivation and water erosion reduced the original slope of 40% to 20% over 3 years. The 6-m between hedgerows means the current riser height of 1.2m could increase to 2.4 m. This may collapse if the soil on the exposed face of the riser dries out. Closer spacing of the hedgerows backed up by a 2-m wide NVS will reduce riser height and lower the risk of a fertility gradient forming on these deep soils. (Palo 19. S. Cotabato)

16 MISTAKES TO AVOID WHEN ADOPTING LAND MANAGEMENT PRACTICES ON SLOPES Photo 16: Planting NVS on long, steep slopes creates high unstable risers between terraces (3-m on this 55% slope).gaps in the clumps of grass allows the fine, fertile soil particles to wash off the hillside leaving infertile sands and gravels behind. Plant steep slopes with tree crops. (Brg Lampitak, Sitio Melina, Tampakan, South Cotabato)