BAR TODAY || Official Quarterly Publication of the Bureau of Agricultural Research

It's no dead-end for the Imperata grassland
by Ma. Lizbeth J. Baroña

July-September 2003
Volume 5 No. 3

www.wssa.net

Did you know that the vast, rolling grasslands that make excellent ground for reflective moments, are truly vast, rolling wastelands? Given the resistant nature of the dominant grass species in these areas, Imperata cylindrica or cogon grass, making decision on the productive use of these lands is not easy.

Finding a way to make these wastelands productive was the aim of the joint study by the SEAMEO Regional Center for Graduate Study and Research in Agriculture (SEAMEO-SEARCA), and the Australian National University Centre for Resource and Environmental Studies (ANU-CRES). It was conducted to determine the biophysical and economic effects of land-use change from Imperata grassland to maize cropping and Gmelina tree plantation.

Persistent, resistant Imperata
Cogon grass, is the dominant grass species in these grasslands. Its enduring and competitive growth is due to its fire climax nature. Fire climax refers to the property in a plant life where fire plays a role in encouraging its growth. Imperata grasslands represent a soil quality that is acidic, degraded, dry, and has low level of organic matter. This is the type of soil that is susceptible to erosion, making it useless except for pasture use. Revegetating the Imperata grassland is also difficult because of its resistance to pests and diseases, and burning.

Models for a lucrative conversion
Pure grasslands occupy 1.8 million hectares of the country's land area.

Conversion of Imperata grasslands into upland crop farms has been proliferating at a fast rate. The obvious reasons for this rapid land conversion are pressure from needs of an increasing population, dwindling resources, and migration of farmers from the lowlands to the uplands.

An upland farming system in Salindingan, Isabela, is an example of a successful conversion of a grassland. The conversion was aided by factors like demographic pressure, land tenure, and easy access of farmers to financial assistance in the form of credit. A similar pattern of conversion was also observed in Misamis and Bukidnon in northern Mindanao.

Apart from turning grasslands into corn or rice farms, planting trees in these areas is also an option. Planting multi-purpose tree species or MPTs, can also be an effective means to revegetate and rehabilitate an area for higher productivity. Tree planting is an effective bio-control for Imperata. The grass may have fire climax properties, but it needs full light to survive. The shade from the trees kills the grass.

The study used three land use models: the Imperata grassland, maize cropping, and Gmelina plantation. The Imperata grassland model is simply an uncultivated and unburned grassland area. Maize cropping refers to the grassland converted into a traditional upland farming system where the soil is cultivated before planting maize seeds, and the Gmelina plantation model, an area where 833 trees of Gmelina arborea, a fast growing tree species were planted per hectare and grown for seven years.

To determine the economic soundness of the land-use systems, the Net Present Value (NPV) of the system is computed using the cost-benefit framework. Products from the land-use systems are bundles of Imperata leaves used a roofing material, maize grain from maize cropping, and fuel and timber from Gmelina. What were costed in creating the systems were tree establishment, pruning, weeding, harvesting, and log processing for the tree plantation; labor, land preparation, and harvesting in maize cropping; and labor in cutting, cleaning, harvesting, and packing of Imperata leaves into bundles, for the grassland.

To determine the biophysical component of the models, the Soil Changes Under Agroforestry (SCUAF) model was used. SCUAF is a simple model that predicts crop yield given changes in soil carbon, nitrogen, and phosphorus content.

The system that worked best
Results of the biophysical component of the study showed that the predicted amount of harvest from the Imperata grassland decreased continuously. The same results were observed for the harvested maize, which also declined throughout the simulation period. As for the Gmelina, there was no annual harvest during the six-year growth. Among the three systems, the Gmelina showed the least decrease in yield. Soil loss was lowest in the Gmelina plantation Continuous cultivation and planting in the maize farm caused the greatest soil loss among the three systems.

In all three systems, the soil carbon decreased throughout the simulation period, the slowest decrease being in the Gmelina plantation. The maize system had the highest rate of deceasing soil carbon, followed by the Imperata grassland. As to the nitrogen content of the soil the Gmelina plantation showed a steady level of nitrogen. The maize system showed the highest rate of decreasing nitrogen in the soil. The same is true with the phosphorus content of the soil, with the maize system losing the most soil phosphorus, and the Gmelina exhibiting the least rate of loss.

Using cost-benefit analysis, the predicted annual income of the Imperata grassland and maize farm was positive, but declined throughout. In contrast, the Gmelina plantation gave no positive returns in the first six years. But the net profit it brought in the 7th year outweighed the deficit it suffered in the preceding years, since the trees were harvested in the 7th year.

Using models to study long term impact of land use change is an important tool for decision making. In this case, options regarding the use of grasslands have widened.

Source: Modelling the Environmental and Economic Impacts of Land-Use Change in Tropical Imperata Areas by: Damasa B. Magcale-Macandog, Canesio D. Predo; and Patrick Rocamora, SEAMEO Regional Center for Graduate Study and Research in Agriculture (SEAMEO-SEARCA) and Australian National University Centre for Resource and Environmental Studies (ANU-CRES)