Summary. Much of south-eastern Indonesia is mountainous
and characterised by a semi-arid tropical environment. Soil erosion is a
significant environmental problem facing the region, affecting both
productivity of the land and water quality. The challenge for the region is to
secure year-round food production in such a fragile environment. More than
90% of rain falls in a distinct wet season between November and April.
Therefore, cropping in this region is dependent on matching crop growth with
water supply. In particular, crop production depends on the efficient use of
rainfall during the wet season, including avoidance of waterlogging, and
efficient use of stored soil water during the dry season.
This paper summarises the results of a series of experiments undertaken in
West Timor, Indonesia, between 1993 and 1999 aimed at developing a raised-bed
cropping system. The objective of these studies was to better utilise the more
fertile alluvial soils that are often susceptible to waterlogging during the
wet season, allowing a range of crops to be grown in addition to rice.
Raised beds of height 0.2 m and width 1.5 m were constructed either manually
or with an 8.5 hp two-wheeled hand tractor. A range of crops including
soybeans, sorghum, maize, pigeon pea, yam bean and cassava were successfully
grown on raised beds in the wet season in addition to rice, indicating that
raised-bed technology overcomes the constraints of waterlogging in the wet
season. Soybeans grew particularly well on raised beds, with December-sown
crops producing almost twice the yield of January-sown crops (2.6
v. 1.4 t/ha). For rice and soybeans, early sown
crops were better able to match growth with water supply, thereby avoiding
end-of-season drought. Early sowing and harvesting of wet season crops enables
a drought-resistant crop such as sorghum to be planted in lateMarch or early
April, utilising the stored soil moisture for grain production and also
maintaining ground cover in the dry season.
It is argued that cropping systems based on permanent raised beds can reduce
erosion in 2 ways. First, raised beds are a permanent structure and, with the
inter-cropping and relay-cropping proposed, crops can provide all-year ground
cover in lowland areas. Second, if sufficient food and cash crops are grown on
raised beds to meet the basic needs of subsistence farmers, then upland
cropping on steep slopes can be replaced by a variety of tree species,
providing additional food, fodder, firewood and medicines. Together, these
strategies have the capacity to enhance food production and security in the
semi-arid areas of eastern Indonesia.
Rainfall, land use and woody vegetation cover change in semi-arid Australian savanna
