Kudzu for restoring soil fertility and controlling cogon in cogon-infested areas

Cogon areas are usually fallow lands, which are considered marginal lands characterized by poor soil fertility and declining crop yields. They are called cogon areas because they are dominated by Imperata cylindrica (L.), locally known as “cogon.” Local people Imperata by crushing it down with a 2-m long, 10-cm wide and 5-cm thick wooden plank, made either of coconut trunk or any straight cylindrical pole. This indigenous control method was observed to be more effective than clearing or cut-and-burn, or grazing animals. Dela Rosa and Itumay (ViSCA) confirmed the effectiveness of the said indigenous method through a study conducted in an Imperata-infested upland area planted to coconut and fruit trees in Baybay, Leyte; and further enhanced the control of Imperata by growing kudzu (Pueraria sp.), a leguminous cover crop, in the Imperata-infested area. Besides being a control measure, the modified method with kudzu restored the fertility of marginal fallow lands.

Findings

• The method consisted of broadcasting kudzu on a cogon-infested area and crushing down the Imperata together with the kudzu and other weeds, six months after the emergence of kudzu, or when the kudzu started to creep over the Imperata. Complete eradication of Imperata was accomplished after three to four repetitions of the crushing operation, at a six-month interval, in a period of two years or less.
• The eradication of Imperata was attributed to the ability of kudzu to creep and twine, thus covering and smothering the Imperata with a blanket of leaves, preventing light to penetrate through, eventually outgrowing and killing the Imperata. However, precaution must be taken to control the overgrowth and encroachment of kudzu on the main crops.
• In addition to controlling the growth of Imperata, the kudzu cover enhanced the decomposition of crushed Imperata and other vegetation.
• The biomass and nutrients released from the decomposing Imperata and other vegetation contributed to the build-up of organic matter as well as the fertility of the fallow land.
• The plots with kudzu gave higher soil organic matter (OM) content, with an average of 4.10% for a five-year period, as compared with the plots without the kudzu, with an average OM content of 2.67%.
• Kudzu, being a leguminous plant, increased the soil’s nitrogen content as indicated by the higher average nitrogen content of 0.19%, as compared with plots without kudzu, which gave 0.12% nitrogen content average during the five-year period.
• The improved soil fertility levels were manifested in the increased number of coconut fruits, i.e., from 2 to 16 nuts/tree, four years after implementing the method. Although, for some other reason this yield level declined. For Szinkum citrus trees, yields were increased from an average of 32.94 kg/tree to 53.13 kg/tree in four years.
• In terms of costs, the “crushing with kudzu” method was relatively cheap, with an estimated cost of P950/ha per year for two operations, with 2 ½ days/operation. On the other hand, the “cutting” method cost was about P2,250.00/ha per year for three operations, with five days/operation.

Source: PCARRD, 2001. Highlights 2000, Los Banos, Laguna.

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