In-row tillage, or iras-iras as it is more commonly called locally, is a minimum tillage system where only about 60 percent of a field is cultivated. It is practiced in Southern Cebu where hillside farms are of heavy limestone (rocky and dry). the technology is also especially applicable to easily erodible areas, i.e., steep to moderately steep slopes. It is not suitable in unstable and loose soils. The iras-iras minimizes erosion, at the same time gradually builds up the soil and ultimately increases yields.
1. Measure a contour baseline on the upper portion of the farm using an A-frame. Develop this line into a contour drainage canal, thick hedgerow or rockwall to protect the lower portion of the Farm from runoff water.
Constructing the rockwall on the contour baseline
2. Measure 100 cm below the baseline and lay out a contour line using an A-frame.
3. Below the contour line, dig a furrow, 40-60 cm wide and as deep as possible.
Marking the contour line and digging the furrow
4. Loosen but do not remove the in the furrow. Remove rocks and place them on the lower side of the furrow.
5. Tamp the soil on the lower side of the furrow.
6. Measure 1 m below the preceding contour line and construct a second furrow as in step 3. Then, develop three more furrows down the slope following the steps previously indicated.
7. Eighty (80) cm below the contour line of the fifth furrow, make another SO cm-wide furrow and develop it into a thick hedgerow or rockwall to further stabilize the hillsides.
8. Repeat procedures 2-7 until the whole farm has been covered.
9. Plant the main crop on the furrows. The uncultivated spaces in between should be planted with cover crops to stabilize them. (Important: organic fertilizers on the furrows two to three weeks before planting.)
MAINTENANCE OF IRAS-IRAS
1. Replant gaps in the hedgerows and repair damaged rockwalls.
2. Replant uncultivated strips between furrows with cover crops to prevent soil from falling into the furrows.
3. Before the iras-iras becomes stable, the soil keeps moving downward. It is necessary to widen furrows. Spread the soil that accumulate on them.
4. Do not pull the weeds that grow as this will loosen the soil and stones on the strips. Just cut the weeds close to the ground.
5. Use the cut weeds and crop wastes/residues as mulch to help preserve the soil moisture.