Chapter 4
Agroforestry

4.4 Annual crops and intercropping

4.4.1 Site improvement for acid infertile soils

Suggest if:

• Soils are acidic and infertile (Oxisols, Ultisols)

Imperata often occurs on very acid, infertile soils with not enough phosphorus (P) available for good tree growth and crop yields. On such soils, a heavy one-time application of rock phosphate (1 ton/ha) can improve the site greatly and help agriculture and agroforestry to succeed.

Soil pH should be tested and a trial should be made of this method before it is applied over a wide area. If rock phosphate is unavailable, triple super phosphate and lime can be used instead. On land that is low in available P but has a pH greater than about 5.5, a soluble P fertilizer such as triple phosphate can be used alone. Where rock phosphate is unavailable or too costly for the farmers, it would be appropriate to seek outside assistance with credit or procurement.

This procedure is best combined with legumes and green manure as in the following example.

Rock phosphate and leguminous cover crop system in Indonesia

Farmers may prefer to plant food crops immediately after the heavy fertilization. In that case, contour hedgerows may be planted instead of the leguminous cover crop.

Rock phosphate and contour hedgerows

Farmers grow upland rice and other crops on very infertile, acidic, hilly soils in East Pasaman, West Sumatra, Indonesia. Yields have become lower over the last 40 years as fallow periods shortened from 15 years to 5-6 years. An extension project assisted them to:

• Clear Imperata and plant contour hedgerows of Flemingia macrophylla

• Broadcast 1 ton/hectare rock phosphate

• Plant peanut and beans in the first year, with fertilizers

• Plant improved varieties of upland rice and rubber seedlings

• Use Flemingia trimmings as mulch and for livestock fodder as needed

High yields of annual crops were achieved. Investment in Imperata rehabilitation was profitable after one year, even with working capital borrowed at 20% interest rates.

4.4.2 Intercropping annual crops with trees

Annual crops can be intercropped with trees to provide short-term income. As the annual crops are planted and weeded, Imperata is kept out and the area has less fire hazard. Fruit, rubber, and other tree crops are an important investment, so cultivation

practices for the annual crops should be careful not to damage or cause competition with the trees. If done correctly, the weeding and fertilizing of annual crops will benefit the tree crop. For example, fertilized chili peppers are a good intercrop for rubber trees.

The farm family may only have enough labor to handle one to two hectares of annual crops. For establishing additional tree plantings, the family may rely on cover cropping (Section 4.3), herbicides and weeding, pressing and fuelbreaks.

To reduce fire hazard, the annual crops should be:

• Less flammable than Imperata.

• Maintained by weeding or mulching to keep Imperata out.

• Followed with another crop or groundcover so that Imperata does not return.

• Productive and profitable enough to make it worthwhile for farmers to maintain the intercrop.

Common intercrops include upland rice, sweet potato, beans, peanut (groundnut), tomato, peppers, squash, and ginger.

To establish an annual crop as an intercrop:

1. Plan for erosion control. On lands over 5% slope, plan to use some form of vegetative barrier on the contour (Section 4.1). On all lands, use mulching and cover crops (Section 4.3) wherever possible.

2. Prepare the field. The companion manual Imperata Management for Smallholders (Chapters 5 & 6; see Appendix A) provides more detail for Imperata control in fields, especially on the use of control herbicides and combinations of techniques.

Field preparation

3. Plant trees. Lay out the rows of trees along the contour. On flat land, make rows from east to west. Use rectangular spacing to make the strips between lines wider and easier to manage for the intercrop. Mark tree planting positions with stakes so that they can be seen while the work is being done on the intercrop. Plant trees after cultivation or spraying is completed. (See Sections 4.6 and 4.7 for more information on tree crops.)

4. Fertilize. Many legume crops can fix their own nitrogen using root nodule bacteria (rhizobia). On lands that have been under pure Imperata for a long time, legumes may do better if inoculated with rhizobia. Get rhizobium inoculant from an agricultural extensionist, or mix soil obtained from a location where the crop has been growing vigorously with the seed before it is planted.

5. Plant annual crops. Do not plant annual crops closer than 1 m away from the tree base, or under the crop canopy.

6. Control Imperata during the life of the crop. Uproot, apply herbicide, or mulch.

7. Harvest the annual crops.

8. Continue to control Imperata. Try relay-cropping (planting a second crop before the first is harvested). Otherwise, follow the crop immediately with another crop, a leguminous cover crop (Section 4.3), or ring-weed the tree crop. Maintain a fuelbreak around the field.

9. Be careful of trees when cultivating the field for additional crops. Stake trees so they can be seen. Do not cultivate closer than 1 m from the stem, or under the canopy of the tree. Cultivation under the tree's canopy will damage the tree's roots.