Improved soil management on rainfed vertisols in Nusa Tenggara

• University of Mataram, Indonesia
• Balai Pengkajian Teknologi Pertanian, Indonesia

Vertisol soils are characterised by their high clay content. They are difficult to manage for agriculture. If they are tilled when dry, then they can form large clods that are difficult to break down. On the other hand, if tilled when too wet, they smear and become impenetrable to water and plant roots.
Vertisols occur over about 320 million ha of land across the world, with 70 million ha in Australia. In Indonesia, they occur mainly in Java and in the Nusa Tenggara provinces, covering about one million ha. The soils here are potentially productive, but difficult to manage under the prevailing wet-dry climate.
In West Nusa Tenggara, the Indonesian 'gogorancah' cropping system is used on the vertisol soils. This is characterised by early sown rice, dry conditions during its early growth, followed by the wet season. After rice harvest, a secondary crop can be grown on the residual soil water. However, the problem is the heavy tillage required to prepare the dry vertisol for sowing the rice before the rains. This is strenuous work requiring many days of labour.
The project therefore sought alternatives to the gogorancah system. It studied one possibility- the use of permanent raised beds for cropping - that could reduce the work required for tillage as well as increase soil organic matter and prevent the soil from baking hard (thereby furthering root growth). The work was modelled on a system just coming into practice for non-horticultural crops in southern Australia.

The project combined study in Lombok and Sumbawa (in Nusa Tenggara) with vertisol cropping in Australia to test whether productivity increased when soil structure and water supply improved. The work also sought a greater understanding of the mechanisms by which organic matter softens and stabilises vertisols, and examined ways to improve agricultural productivity through better alternatives to the tillage and cropping systems existing in Lombok and Sumbawa.

The project started with a review of the literature to benchmark crop yields on vertisols with limited water. Using knowledge from this, crops were selected for use in pilot experiments on replicated plots in Lombok and Sumbawa. The plots were divided into four parts - one kept the gogorancah system as a control, and the remaining three undertook studies on varieties of permanent raised beds. For comparative analysis, costs and labour for each of the four treatments were recorded, along with yields and profits. The scientists also measured soil physical conditions, water status, and run-off.
A separate sub-project concentrated on complementary, smaller experiments to test the effect of different types of mulch, the rates of their decay, the best size for the raised beds, the optimum conditions for seed germination, and the effects of varying sowing depth, sowing techniques and sowing time.
The fourth phase of the work consisted of laboratory and glasshouse experiments in Australia to understand why and how the biological and structural health of vertisols worsens when they are tilled, continuously flooded or when organic matter is destroyed. This work helped to determine the mechanisms by which vertisols become massive under the gogorancah cropping system, and become soft and friable under unflooded permanent beds and minimum tillage.

In field experiments at two rainfed sites in southern Lombok the growth and yields of staple crops were compared - for rice (wet season) and soybean (dry season), on both permanent raised beds (PRBs) and flat land. The yield of rice, but not soybean, was lower on PRBs than on flat land. However, due to good drainage in the wet season, and harvested water for irrigation in the dry season, the research team found that profitable vegetable crops could be grown on PRBs - both out of season in the wet season.
Hence they developed the ACIAR Cropping Model (ACM), where valuable vegetables are grown on 1/3 ha on PRBs (1.2 metres wide) out of season in the wet season, while rice and soybean are grown on 2/3 ha on flat land. During the dry season water is efficiently used to grow one or two sequential vegetable crops on PRBs. Economic analysis showed that vegetables or fruit grown using the ACM are more profitable than rice grown under gogorancah.
Groups of participating farmers at three sites set up the ACM on demonstration farms. These farmers had access to water either from an embung (dam), from groundwater from a well, or from illegal (but tolerated) access to water from the irrigation scheme. Crops on PRBs were irrigated from furrows or with water poured from a cup. The Local Team used the demonstration farms for the following reasons:
to introduce the ACM to a wide range of rainfed farmers
to discuss problems raised by farmers
to help farmers to improve all management on their farms, and to plan their cropping.
The ACM has doubled farmers' incomes and improved their nutrition, with less hard labour than those employing gogorancah. One big advantage of the ACM is that farmers can produce three crops per year, whereas without the ACM they can only produce a maximum of two crops per year.
To increase the adoption of the ACM the Local Team negotiated with local and international seed companies, central and local governments, local banks and restaurants. This led to help for farmers through better prices for crops, prices advertised daily in the local press, more markets, cheaper and easier bank loans, one-off payments when crops fail and increased water supply and storage capacity. Originally 24 participating farmers set up the demonstration farms, but many other farmers from several villages (including on soils other than Vertisols) have now adopted the ACM and others are keen to learn. Farmers who previously would not sacrifice some of their farm for storage capacity for harvested water now see the benefit.
A Vendor System was developed for farmers, whereby suppliers of agricultural inputs are not paid until after harvest, and traders make it easier for farmers to sell their crops. Following surveys of four major fresh markets, agricultural extension officers can now specify which vegetable crops, and when, farmers should sow. This will avoid oversupply of certain crops at certain times of the year. New markets include restaurants in villages and in Mataram (the capital of Lombok), Open days at the university, and the seed companies.
Water is the major limiting factor for the ACM. A separate study (SMCN/2002/033) is using modelling to report on the full impact of harvested water on the irrigation scheme on Lombok, and is undertaking a cost/benefit analysis of the whole irrigation scheme. Modelling of climate data in this project showed that because of drought, no excess water could be harvested in the wet season in about one in four years. As well, on average only half the water needed for full irrigation in the dry season could be harvested to allow crops in the dry season to be well established and partially irrigated to produce reasonable yields.
Linkage of this project with SMCN/2002/033 has led to the establishment of the Research Centre for Water Resources and Agroclimate (RCWRA) at University of Mataram. The research team of the RCWRA brings together all the scientists involved in the two ACIAR projects, as well as key external collaborators. This enhanced capacity has positioned Uni Mataram to work towards a potential follow-on project involving Japanese universities.