Soil testing and plant analysis for small-scale farmers
Overuse of chemical fertilizer is a common problem all over the Asian and Pacific region. Another problem is that fertilizer applications are often unbalanced. In particular, too much nitrogen fertilizer is often applied at the expense of other nutrients.
Soil testing is the basis for good fertilizer management that maintains the productivity of soil and improves the quality of crops. It promotes more efficient fertilizer use at a lower cost, and prevents environmental pollution from excess fertilizer. Crops which are provided with the nutrients they need at the required rates are stronger, and more resistant to pests and diseases.
This seminar was held in order to discuss the access by farmers in the region to soil testing and plant analysis services, and ways in which they might gain improved access to such services. In this way, farmers will be able to achieve a better match between the fertilizer requirements of their crops, and the type and quantity of fertilizers they apply.
In the early days of soil testing in the region, soil diagnosis was needed mainly to identify nutrient deficiencies of the soil. This is still a very important function of soil testing. In all crops, the growth of the plants is limited by the nutrient element present in the smallest quantity, even if all other nutrients are available in adequate amounts ("the Law of the Minimum Nutrient").
However, in Japan and several other Asian countries, farmers have been applying large amounts of chemical fertilizer for decades. As a result, the soil nutrient status is high. Soil nutrient problems are as likely to involve toxicity (excess) as deficiency.
Surplus nitrogen can contaminate groundwater and rivers, in the form of nitrate and nitrite. Excessive fertilizer can also cause quality problems in the harvested crop, especially fruits and vegetables. In the case of fruit, too much nitrogen may cause the growth of too much vegetation, and poor flowering and fruit set. Applying abundant nitrogen to rice may cause problems of rice blast, and also promote infestations of plant hoppers. The soil nitrogen balance is showing a surplus in most developed countries, but with the help of soil testing, this surplus is now becoming smaller.
The first stage of a soil testing service consists of soil surveys and field trials, so that standard fertilizer recommendations can be established for important crops growing in different types of soil. Initially in Asia, the focus is generally on rice production. Later on, recommendations are developed for other crops.
All countries represented at the seminar provide standard recommendations based on crop type and soil type. In Indonesia, for example, a national program conducted since 1970 has carried out soil testing and soil surveys. The results serve as the basis for fertilizer recommendations, and also for monitoring fertilizer quality.
Accuracy and flexibility may be improved by the use of expert systems. In Malaysia, an expert system known as FERTO (Fertilizer Recommendation Tool) has been developed for high-yielding rice production.
A further step is soil testing and plant analysis for individual farmers. The cost of soil testing is high in relation to farm incomes in Asia, and soil testing for small-scale farmers is usually supported by government funding. The service is either free to the user or heavily subsidized.
In Japan, soil testing services have a three-tier structure. Simple soil testing services are carried out by agricultural cooperatives, which provide their members with information on major chemical properties of soil such as the pH and the available phosphorus (P). More detailed soil testing is carried out by agricultural extension offices, which can analyze the major elements and important physical properties. The most sophisticated level of analysis, including trace elements and microbial characteristics, is carried out by the agricultural experiment stations.
In Taiwan, a similar soil diagnosis network is operated by the Taiwan Agricultural Research Institute (TARI) and the various district agricultural improvement stations. Soil samples are collected by farmers and extension staff, and sent to TARI for analysis. The interpretation of the results and fertilizer recommendations are computerized. The recommendation sheets are sent back to the district stations, and after confirmation are distributed to farmers. This soil testing service is free of charge to farmers.
In Korea, soil testing is carried out by county agricultural research centers, under the Provincial Governments. The National Institute for Agricultural Science and Technology (NIAST) has also developed an on-line soil information system, which provides detailed soil management information using GIS technology via the Internet. This gives farmers information about the fertility status of their farm, the management history, the soil type, and fertilizer recommendations, as well as recommendations for land use.
Traditional soil testing methods often involve a considerable time delay between sending in the samples and receiving the results. This means that the results often cannot be used as a guide for fertilizing the growing crop. There is a growing interest in real-time plant nutrition analysis, using samples taken from intact plants growing in the field (using e.g. some of the petiole, or juice taken from the plant). In this way, analysis can be carried out in the field, and farmers can decide within a day whether top-dressing is needed.
One program which is attracting considerable interest is Thailand's program of vans which serve as mobile soil testing laboratories. These visit villages in rural areas, analyze soil samples and make fertilizer recommendations. The program is operated by the Department of Land Development (DLD).
The "Dr. Soils" are farmers selected from each village who are trained in the basic soil testing program and land development techniques. After ten years of operations, there are now 63,000 Dr. Soils from 67,000 villages. The Dr. Soils programs is now serving farmers all over Thailand.
Farmers are taught how to take soil samples, several weeks in advance so the samples have time to dry before they are tested. On the day when the mobile laboratory is scheduled to visit their village, farmers take their soil samples to the van at some central point, such as the local temple or school. While farmers are waiting for the samples to be analyzed, DLD staff take the opportunity to educate farmers about soil testing and fertilizer use.
Fruit production is becoming increasingly important in many countries in Asia, including Vietnam. Vietnam has developed detailed fertilizer recommendations for various kinds of fruit trees growing on a range of soils. A common problem is that growers apply too much nitrogen fertilizer at the expense of other nutrients, while phosphorus deficiency is common.
Since fruit trees are a perennial crop, their performance in any one year is partly determined by the level of fertilizer they received in previous years. The higher the yield in any one year, the more nutrients are needed in the following year. Trees also need more fertilizer as they grow in age and size.
Both leaf analysis and soil testing are being used in the Philippines as the basis for fertilizer recommendations covering a range of perennial crops. Calcium deficiency is a common problem in fruit crops. The availability now of local data for soil and plant analysis is likely to encourage fruit farmers to use location-specific fertilizer recommendations.
Plant growth abnormalities indicate one or more constraints, in terms of unfavorable growing conditions. These may be a lack or excess of an essential plant nutrient. Several papers discussed the visible symptoms in the growing plants of nutrient disorders. However, similar symptoms may also be caused by unfavorable conditions (such as an environment with temperatures which are too high or too low, or soil with a pH which is too high or too low).
If soil testing detects a nutrient deficiency, this can be immediately remedied by applying the nutrient in fertilizer. However, detailed soil testing for a range of nutrients is expensive. Several participants at the seminar recommended the application of organic fertilizers such as composted chicken manure as part of an effective fertilizer management program. Organic fertilizer not only improves the soil physical properties, but supplies a range of micronutrients. While each of these is needed by the crop only in very small amounts, the absence of any one of them will have a very damaging effect on crop performance.
In all countries, soil diagnosis is intended, not just to improve crop performance, but also to improve long-term soil productivity. Korea has developed a system of integrated soil management, adapted to the different kinds of major paddy soils. For example, compost application is particularly important for clay soils with limited soil reduction. Phosphorus applications are also important for such soils. Silica applications are recommended for sandy soils, highly productive soils, and poorly drained soils. Sandy soils are also given remedial applications of clayey earth from hillsides, and applications of lime, while four-split applications of nitrogen are recommended.
An interesting aspect of Korea's system of integrated soil management is that relative yield increases were most marked when climatic conditions were unfavorable. In other words, integrated soil management seems to give rice crops more resistance to cold weather. The benefits of integrated soil management were seen throughout the country, regardless of the soil type.
The main constraint to the widespread use of soil testing services in Asia is the cost. Average farm size in Asia is small: in Indonesia, the average farm size is only 0.5 hectare. Generally, small-scale farmers are not able to afford the cost of soil testing. This means that soil diagnosis services for individual farmers are generally limited to industrialized countries which can afford to provide a free national testing service. Participants felt that the "Dr Soils" program in Thailand is an effective way of giving small-scale farmers better access to soil testing services, by means of mobile soil testing vans which visit villages.
Participants were agreed on the importance of teaching farmers to take proper soil samples. If the sample is not taken properly, all subsequent analysis is useless. Farmers also need more information about the effect of plant nutrients on crop growth, and a knowledge of the fertilizer requirements for the particular soil type(s) of their farms.
It is common for soil maps to be used as the basis for fertilizer recommendations, supplemented by field testing. However, many agricultural soils in Asia have been cultivated and fertilized for hundreds of years. One paper presentation from Thailand suggested that in the case of Thai soils, past management and land use have more effect on soil fertility than the soil type. This may well be true of other parts of Asia with a long history of agriculture.
One of the aims of soil testing is sustainable agriculture which improves the environment. Fertilizer applications which are environmentally friendly are lower than those which give the maximum yield. The result of 90 field experiments carried out in Korea showed that the level of nitrogen fertilizer for environmentally friendly agriculture was only 95% of that for maximum yield. This yield gap means that farmers must bear a financial loss if they practice environmentally friendly fertilizer management, unless market forces can somehow be adapted to give their produce a relatively higher price. In Japan, labeling and pricing of agricultural products, especially fruit and vegetables, is beginning to reflect methods of production, including the reduced use of chemical fertilizer and the quality of the fruit such as the Brix.
Micronutrient deficiencies are easily corrected, but difficult and expensive to diagnose. Applications of chicken manure seem to be a low-cost and effective method of correcting micronutrient deficiencies, while improving the physical properties of the soil.
Held at the International Technical Cooperation Center (ITCC), Rural Development Administration, Suwon, Korea, on August 11-15.
No. of countries participating: 9 (Indonesia, Japan, Korea, Malaysia, Philippines, Taiwan ROC, Thailand, USA, Vietnam)
No. of papers presented: 15
No. of participants: 20 plus observers
Co-sponsor: Rural Development Administration, Korea
Figure 1 The "DR. Soils" Program. Mobile Soil Testing Laboratory Which Visits Rural Villages, Thailand
Figure 2 Thai Farmers Waiting to Hand in Their Soil Samples
Figure 3 The Scientific Team Analyzing Soil Samples in Village