Use of reactive phosphate rock for the rehabilitation of anthropic savannah in Indonesia.

During the past decades, the agricultural sector in Indonesia has made substantial progress that permitted the achievement of self-sufficiency in rice production in 1984. This has come through successful intensification programmes in the lowlands.

The government of Indonesia to improve food production and to face an increasing demand for non-rice food initiated transmigration and agriculture extension to the outer islands like Sumatra, Kalimantan, and Sulawesi.

There are millions of hectares of former forest land in Indonesia now covered by unproductive grasslands and savannah and referred to as Olahan tiduru (sleeping land). A large proportion of this land has only slight topographic limitations whilst climate (solar radiation, rainfall and temperature) is nearly optimal for large crop yields. The main constraint to sustained large yields is poor soil fertility and the lack of appropriate management techniques to minimize soil erosion.

Improper soil management due to the lack of appropriate technology resulted in severe soil degradation in the uplands, and a large part of these lands have been abandoned and have now become grass cover lands consisting of Alang-Alang (Imperata cylindrica).

From 1988 to 1994, the World Phosphate Institute (IMPHOS) with a close collaboration of the Center for Soil and Agroclimate Research (CSAR), the Potash and Phosphate Institute (PPI), and the American Phosphate Foundation (APF), conducted an important project in Indonesia on "The Use of Reactive Phosphate Rock for the Rehabilitation of Alang-Alang land".

The project was implemented in PT. Gunung Madu Plantation, and in Terbanggi, both sites in Lampung Province. This project demonstrated that a single heavy dosage (1 ton per hectare) of reactive rock phosphate is the most economic and effective technology for rehabilitating abandoned land.

Soil rehabilitation involved the following steps : burning first weakened Imperata Cylindrica and the regrowth sprayed with glyphosate herbicide. Phosphate and calcium (Ca) deficiency was then corrected by a single large application (1 t ha-1) of reactive rock phosphate (RPR) or the equivalent (in monetary value) in the form of triple super phosphate (TSP) and lime.

P.RESIDUAL EFFECT ON 5 SEASONS CUMULATIVE FARM. INCOM, INDONESIA 1989-91

The results of this work suggest that at least 9 million hectares of degraded land (sleeping land) in Indonesia could be rehabilitated and produce at least 5t grain equivalent per hectare and per year, or 45 Mt total grains equivalent. Clearly, substantial improvements in soil fertility are first required, but before a large-scale adoption of soil fertility amelioration can take place, several factors must be changed or modified.
The attached figure 1 summarizes the importance of this technology, in economic term.
At Terbanggi, the beneficial effect of P fertilization over five cropping seasons was valued at US 3086/ha or USD 2130 more than where no P was added. With a different cropping sequence at Gunung Madu, P addition resulted in an income of US$ 2276 representing an increase of US$ 1681 more than what was realized in the absence of P.

* Rehabilitation of Alang-alang infested land using a combination of living mulch
  (Mucuna ssp.) and P application
** One time application per ha of 400 kg TSP + 1 t lime or
*** 1000 kg of reactive rock phosphate (RP).

Table 1 : Effect of Phosphorus Application from Different Sources on the Available P Content in Top Soil ( 0-20 cm) at Terbanggi, Lampung (1988 - 1992).
As shown in the table 1, one time initial applications of TSP + Lime or rock phosphate had marked residual effects on available soil P.
The Agronomic Effectiveness of RP was comparable to TSP and persisted over 7 cropping seasons after the initial P application.
A large initial application of P on acid upland soils has been argued repeatedly in the literature (World Bank, 1994) and this work has shown some of the returns from such an investment. Economic evaluations of a capital investment in phosphorus fertilizer should not focus on immediate financial gains alone (Fox, 1988) but also on the positive externalities associated with increased agricultural productivity in remote areas, which are the current focus for poverty alleviation and environmental conservation.