Keywords: Dr. Soils, mobile soil testing laboratory, soil maps, soil samples, soil test kit, Thailand

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A SOIL TESTING SERVICE FOR FARMERS IN THAILAND,USING MOBILE LABORATORIES

Narong ChinabutOffice of Science for Land Development

Land Development Department, Ministry of Agriculture and Cooperatives,Bangkok 10900, Thailand

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The Land Development Department of the Ministry of Agriculture and Cooperatives, Thailand, hasbeen highly successful in transferring soil management technology to Thai farmers through the“Dr. Soils” project. The “Dr. Soils” are farmers selected from each village who are trained inbasic soil testing and land development techniques. The program has been operating for tenyears. There are now 63,000 Dr. Soils from 67,000 villages. Dr. Soils are volunteers, whorepresent LDD in their villages and act as channels of information between LDD and farmers.

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The soils of Thailand vary widely, dependingon the parent material, the climate, thevegetation and the topography. They areclassified into more than 360 soil series.Approximately 41% of the country is arableland, only 10% of which is irrigated. The soilswhich are well suited to agricultural productionmake up 14% of the total, while soils whichcan be used for agriculture but needimprovement and conservation make up 36%.

The Land Development Department (LDD)of the Ministry of Agriculture andCooperatives is responsible for soilclassification, soil conservation and soilimprovement for agriculture. The soil datacollected by LDD is available for the benefit ofall government organizations, as well as theprivate sector.

Results from the analysis of 83,600 soilsamples taken from farms between 1987 and1990 indicated that the chemical properties ofmost arable soils in Thailand are as follows.Ninety-four percent are very low inphosphorus, 92% have a very low organicmatter content, and 61% are very low to lowin potassium.

These properties are the result of severalfactors. First, many soils in Thailand arenaturally low in plant nutrients because theparent materials from which the soil were

formed are low in phosphorus (P). For thesame reason, many have a medium to lowpotassium (K) content. Secondly, the hightemperature and high rainfall cause the releaseof nutrients into groundwater, and leaching andrunoff of nutrients from fields, especially wherethey have been cropped continuously and thesurface has been allowed to erode.

The nitrogen (N) supplying capacity ofsoil is closely related to its organic mattercontent. This is very low in most soils,because of the rapid rate of decompositionunder high temperatures and rainfall.Practically all soils in Thailand must beimproved for optimum production.

In the past, recommendations forfertilizers and soil amendments in Thailand werebased on data and 1:50,000 soil maps.Intensive cropping over the past 30 years hasbeen accompanied by an increased use ofchemical fertilizer. Incorrect managementpractices and fertilizer use caused localvariations in soil fertility, especially invegetable fields and fruit tree orchards. Somenutrients became depleted while others built upin the soil, depending on the amount suppliedin fertilizers and the amount removed inharvested crops.

Most agricultural soils in Thailand havebeen in continuous production a for long time.Soil erosion control in sloping land has notbeen widely practiced on most farms. Some

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farms have been fertilized, but others havereceived little or no fertilizer and lime. Becauseof this history, past land use and managementpractices have more influence than soil type onsoil fertility.

The original soil survey data, based ononly one set of samples of the soil andsubsoil per square kilometer, does not giveadequate information about the soil propertiesof every farm. Fertilizer recommendationsbased on soil type are not suitable for Thaifarmers. Recommendations of how muchfertilizer and lime and other soil amendments toapply to particular crops on each farm shouldbe determined by individual soil tests.

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In 1964, LDD set up a central soil testinglaboratory. At this time, routine soil and plantanalysis was carried out in support of soilsurveys and soil classification projects, andresearch on soil amendments and soilconservation. Only a few soil samples wereanalyzed as the basis of fertilizer recommen-dations.

Problems of soil degradation led to anincreasing awareness that action had to betaken to increase crop productivity through theuse of fertilizers and soil amendments. In1992, LDD set up a smaller laboratory in eachof the 12 Land Development Regional Offices(LDRO). A year later, LDD launched a project“Improvement of Soils and Fertilizer TechnicalServices”. The main objectives were toemphasize the minimum use of chemicalfertilizer, increase the use of organic fertilizer,and conserve the land under a system ofsustainable agriculture.

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The Office of Science for Land Development,LDD, takes responsibility for the soil analysisservice, and provides farmers withrecommendations for soil improvements and soilconservation.

Soil samples sent from farms are routinelyanalyzed to determine their texture. They arealso given minimal chemical analyses to assessthe soil fertility. Recommendations are madeas follows:

Nitrogen (N)

LDD laboratories do not analyze soil Nas the basis for recommending how muchfertilizer N to apply. Scientists have beenunable to develop a reliable test fordetermining the ability of different soils tosupply nitrogen. The rate of N released foruse by crops is affected by the soil organicmatter content, the temperature, the soilmoisture content, the period of crop growth,and many other factors. All of these make itimpossible to predict the amount of N that willbe supplied by the soil to the growing crop.

Secondly, most soils in Thailand are lowin organic matter, and do not vary much intheir capacity to supply nitrogen. Therefore,nitrogen recommendations by LDD laboratoriesare based primarily on the crop requirementsand the length of time under cultivation. Theeconomic rates recommended should beadjusted periodically, according to experienceand field experiments.

Nitrogen fertilizer is generally notrecommended for legume crops, since theyobtain most of the N required for their growthfrom the air, which is about 80% N. A smallamount of 20-25 kg N/ha may be applied asthe starter fertilizer in plots planted in legumesfor the first time, especially if the seeds havenot been inoculated with rhizobium.

Phosphorus (P)

The phosphorus (P) content of practically allsoils of Thailand is inherently low.Phosphorus deficiency is a common limitationto the productivity of most Thai soils, and theapplication of P fertilizers is often necessary.Phosphorus recommendations made by LDDlaboratories depend on soil test values and theP buffer capacity. If soils contain largeamounts of oxy-hydroxides or are calcareous,more P fertilizer may need to be applied tomeet crop requirements.

Potassium (K)

The alluvial soils of the Central plain aredominated by clayey kaolinitic andmontmorillonitic soils, and are used for growingrice. Thirty years ago, most of these soils

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were high in potassium. This was reflected inthe compound fertilizer recommended for rice,which was 16-20-0 and 20-20-0 (N-P

2O

5-K

2O).

The response of crops to potassium has beentested in many experiments throughoutThailand, and it seems that most Thai soils aredeficient in K. The sandy soils of theNortheast are more deficient in K, while claysoils are generally less deficient. As cropyields have grown as the result of higher Nand P fertilization, the need for K in somesoils has increased.

Calcium (Ca) and magnesium (Mg)

Fortunately, most soils of Thailand are notdeficient in either calcium or magnesium.Calcium and magnesium deficiency are generallyfound in the sandy soils of the Northeast,which have a very low pH.

Micronutrients

Most soils of Thailand contain an adequateamount of micronutrients for most crops. LDD,the Department of Agriculture and KasetsartUniversity have conducted research on theresponse of crops to micronutrients in soils.This research emphasized “problem soils” i.e.acid sulfate soils, calcareous soils, sandy soilsand peat soils.

Field trials have shown that themicronutrients most often deficient are iron(Fe), boron (B) and zinc (Zn), and then onlyfor a few crops on particular soils. Researchfor copper (Cu) deficiency in peat soils hasbeen conducted in southern Thailand, but morework is still needed.

Micronutrient analysis is expensive, andis not always reliable enough to serve as abasis for fertilizer recommendations. LDD soiltest laboratories, therefore, do not generallyanalyze soil samples for micronutrients. Themost practical recommendation for these minornutrients is to apply them to specific cropsaccording to the results of experimentsconducted on particular soils.

Lime recommendations

Practically all Thai soils, except for calcareoussoils and some saline soils, are from slightly tostrongly acid. Most crops may need theapplication of lime. More than one-half of thesoil samples analyzed by LDD soil testinglaboratories show that lime is needed.However, most research indicates that it isnon-economic to apply lime to Thai soils if thepH is higher than 5.5. Therefore, LDD soiltesting laboratories recommend that lime beapplied to most crops only if the soil pH isless than 5.5. Marl and ground limestone aregenerally recommended as the best limingmaterials for Thai farmers. If the magnesiumcontent is low and lime is required,applications of dolomite are recommended tocorrect soil acidity.

Mobile soil testing laboratories

LDD has accelerated the project“Improvement of Soils and Fertilizer TechnicalService” by setting up mobile soil laboratoriesto provide an on-farm soil testing service tofarmers (Fig. 1 and Fig. 2). There are now 18mobile soil laboratories in service, analyzing a

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total of 73,000 soil samples each year over thewhole country. Mobile soil testing is a wayof transferring technology for soil improvementwhich enables scientists and farmers to workclosely together and to share information (Fig.3 and Fig. 4).

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In view of the limited manpower and budget ofLDD, help from farmers is needed to achievethe goal of soil improvement. Since 1997, LDDhas carried out the “Dr. Soils" Project. This isnow well-known and widely recognized inThailand.

About "Dr. Soils"

The term “Dr. Soils” refers to the officers ofLDD and the volunteer farmers who participatein land development programs.

Since 1977, farmers (male or female), whomust be at least 20 years old, have beenselected from each village to act as Dr. Soils(Fig. 5 and Fig. 6). Altogether, 63,000 farmersfrom 67,000 villages have joined the program.The Land Development Regional Offices haveprimary responsibility for selecting and training

these farmers.They are trained to understand basic soil

testing and land development techniques.They represent LDD in their villages, to helpgive farmers a better understanding of soilmanagement, and to follow up landdevelopment practices. They are themessengers in distributing the informationabout land development to the villages, andtransferring messages regarding land useproblems from the farmers back to LDD.

Of these 63,000 Dr. Soils, 7,125 farmershave been selected to represent sub-districts.They have been trained in how to use soilmaps (1:50,000), and how to use a soil test kitto test the pH, and analyze the levels of N, Pand K (Fig. 7 and Fig. 8).

They use soil maps and posters to showthe suitability classes of different soils forvarious crops as a means of educating farmers.With the soil NPK test kit, they are able totest the soils on farms around their villages,and give local farmers basic fertilizerrecommendations. All Dr. Soils are volunteers.They receive no salary, but LDD offers toconstruct a small pond on their farms as anincentive.