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SITE-SPECIFIC MANAGEMENT OF RICE FERTILIZERSBASED ON GIS SOIL INFORMATION

Mu-Lien Lin and Tsang-Sen LiuTaiwan Tea Experiment Station

324, King-Long Community,Yang-Mei, Taoyuan, Taiwan, ROC

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Rice is the staple food in Taiwan, witha total planted area covering two croppingseasons of 339,949 ha in 2000. This was thelowest rice acreage for more than 50 years(COA 2001). Rice production in Taiwan isfacing the challenge of cheap imports of upto 140,000 mt per annum under WTO. Inresponse, the government is planning a systemof fallow on a township basis.

Although rice production in Taiwan maynot be as high as in the past, rice is still themost important crop, and the largest user offertilizer. In 2000, rice growers spent anestimated US$64 million on fertilizers. Thisincluded 41,793 mt of nitrogen (N), 15,314mt of P

2O

5 and 16, 462 mt of K

2O (Lin

2001). Not only is rice the staple food inTaiwan, it also provides raw materials forfood processing, and supports ruraldevelopment, social stability, ecologicalconservation and the cultural heritage.

Fertilizer represents only 7% of the totalinput costs for rice (Lin 2001). However,there are many indications that the use of Nfertilizer could be reduced and rice yieldsincreased at some sites through improvedtiming and management of nitrogen fertilizer.

Maintaining an appropriate rice acreage andadopting proper rice nutrient management isthe key to the sustainable development of therice industry in Taiwan.

Dai and Lin (1992) reported that inparts of central Taiwan, most rice farmers usesplit applications of nitrogen four times foreach crop, and make two applications of Pand K fertilizer. The average amounts of N,P

2O

5 and K

2O applied were around 220, 60

and 110 kg/ha, respectively. In anothercounty further north, the survey found aslightly lower application rate (180:60:110 kg/ha). In general, rice farmers’ in Taiwanapply about 20% more fertilizer than therecommended rates. Reducing fertilizerapplications will cut down on productioncosts. In addition, rice offers a uniqueopportunity for the development of site-specific management (SSMG) technologies,because it is cultivated over such a large area.Furthermore, rice production in Taiwan ishighly mechanized.

Factors affecting crop yield and qualityare site-specific (Reets and Fixen 2000). Soiland fertilizer management are two importantfactors in a successful site-specificmanagement strategy. Site-specific nutrientmanagement has several advantages. Not only

Keywords: GIS, rice, site-specific nutrient management, soil information, Taiwan

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Rice is the staple food in Taiwan, and the most important crop. Fertilizer represents only7% of the total input costs, but there are indications that nitrogen applications could be reducedand yields increased at some sites. The paper discusses the use of GIS to develop more effectivefertilizer recommendations for rice. The spatial distribution of phosphorus and potassiumavailable to rice crops was measured by EMI (electromagnetic induction). This allows for in-fieldvariations in the levels of soil nutrients to be taken into account when deciding what additionalnutrients should be applied in the form of fertilizer. There is a need for a greater range ofcompound fertilizers for rice growers in Taiwan.

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can it increase farmers’ profitability, but it canalso reduce the environmental impact offertilizer applications. In 2000, an experi-mental plot of 10 ha was set up in 2000 atthe Taiwan Agricultural Research Institute toinvestigate site-specific nutrient managementfor rice. This Bulletin discusses some of ourpreliminary results.

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A number of agricultural organizations inTaiwan, including agricultural universities andgovernment research institutes, establishedTALRIS (http://talris.besa.nchu.edu.tw), SIQS(http://www.tari.gov.tw/tal.html) and TALMIS(http://www.hdais.gov.tw) systems. These areweb-based GIS systems which attempt to shareand disseminate information on soil propertiesto potential users, particularly soil scientists,extension staff and leading farmers.

TALRIS is the Taiwan AgriculturalLand Resources Information System. It is amap-based retrieving system which providesgovernment decisions associated withagricultural land-use policies, such as cropsuitability analysis, agricultural land releasesand land rating. The overall development ofthe system relies on land evaluation and siteassessment for the planning of agriculturalland-use in Taiwan. Thematic maps relevantto rice production are displayed in Fig. 1 andFig. 2 (Lin and Tsai 1994). This can beused to evaluate the levels of nitrogenfertilizer needed for rice fields in specificareas. The green, blue, yellow and red iconsin the legend stand for 1-4 grades ofsuitability, respectively.

SIQS (Soil Information Query System) isa soil properties query system, developed bythe Taiwan Agricultural Research Institute in1997 (Guo et al. 1999). It enables users toask for information about major soil propertiescovering 12 attributes, including the pH, typeof parent rock, soil texture, drainagecharacteristics, and levels of calcium carbonateand organic matter, in the top four soil layers.It covers all soil series in all counties andcities of Taiwan. The system is a web-service system. Maps of soil properties arematched with political boundaries, as well asthe road network, for convenient identificationof the location of specific fields.

A powerful new system called

“Agricultural Environment Expert System” isnow under development by several universitiesand research institutes. It will include GIS-based diagnostic expert systems, and will beable to offer users fertilizer recommendationsfor different crops for different soils inTaiwan (Guo 2001, pers. comm.). The soildatabase in this system is based on a gridsize of 6.25 ha.

TALMIS is an off-line system using theMapbasic programming package (MapInfo1993) as a development tool. The systemwas constructed according to long-termintensive surveys, with minimum units of 6.25ha, in two counties on the east coast ofTaiwan. This survey work, which began in1992, has attempted to build up an integratedspatial soil database for identifying soilconstraints and adopting ameliorativetechnologies needed to improve cropproduction. Fig. 3 and Fig. 4 show the soilP and K response information in Chian, atownship in eastern Taiwan. This providesrecommended management of nutrients, andfertilizer application for compound fertilizers,P and K in the area.

The east coast of Taiwan has a numberof problem soils. Fig. 5 shows thedistribution of extractable zinc in HwalienCounty (Chen 1997). It shows thatconsiderable areas can be identified aspossibly deficient in zinc.

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In Taiwan, soil test recommendations forrice production were developed in the 1970s.At present, Taiwan’s recommendations fornitrogen fertilizer are specific for the type ofrice (Indica or Japonica), the region and thecropping season. These recommendations areavailable from District AgriculturalImprovement Stations (DAIS), or from theCrop Fertilization Manual published by theCouncil of Agriculture. The recommendationsare also posted on the “Rational Fertilization”web-page of the Taiwan Agricultural ResearchInstitute at http://www.tari.gov.tw, and on thewebsites of each DAIS.

Table 1 gives the nitrogenrecommendations for rice production indifferent regions of Taiwan. Generally, morenitrogen fertilizer is recommended for the first

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crop than for the second crop, as the firstcrop tends to have a higher yield than thesecond. Rice yields are normally lower in thenorth of Taiwan, which has a slightly coolerclimate. As a result, recommended N appli-cation rates in the north are relatively low.

The soil test used to determine levels ofphosphorus (P) in the soil is the Bray 1method. If ICP is used for element analysis,a universal Mechlich extractant is used forextracting soil solution for measurement.Based on tested P levels, ranging from verylow to very high, five rates of P

2O

5 are

recommended (Table 2).The soil test used to determine the

levels of potassium (K) is an extraction usingthe Mechlich method. Currentrecommendations allow the rice grower toapply potash fertilizer based on the results of

the tested K in the soil of his fields (Table3). Recent surveys in Taiwan have clearlydemonstrated that indigenous supplies of Pand K are highly variable on different ricefarms (Lin et al. 2001). Therefore, newconcepts and tools are needed for site-specificnutrient management for rice. A decisionsupport system for site-specific fertilizermanagement for rice as a field level is nowunder development.

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The spatial distribution of availablephosphorus and extractable potassium at afield level is an important feature of site-specific nutrient management decisions.Phosphorus tends to show greater stability

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* An extra 30 kg/ha K2O per hectare is added for poorly drained soil** For sandy shale alluvial soil and red soil in the Hsinchu and Taipei areas, the intermediate level of K is 30-70 ppm. A high level is more than 70 ppm.Source: COA (2000)

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than potassium. The development of aninformation-based system which allowsgrowers to manage resources better, optimizingtheir yields and profits, is the first step inadopting site-specific nutrient management.

EMI (electromagnetic induction) is aconvenient and low-cost method of measuringsoil variability. The EMI technique is a non-invasive and non-destructive sampling method.Soils which contain a lot of sand have moreresistance to an electrical current than soilswhich contain a lot of clay. Calibrating anEM meter for a specific soil series needs tobe based on the EM sensor reading, and the

particular soil attribute of interest. EMItechnology has been widely used in precisionfarming for upland crops in the United States(Davis et al. 1997). Only a fewmeasurements were available for rice fields.

In 1999, the United States Departmentof Agriculture began to evaluateelectromagnetic induction and electricalresistivity in rice fields in Missouri. In thisway, detailed maps were created whichillustrated the spatial distribution of soilproperties. This information may help identifyoptimum fertilizer rates in various areas.

We have used a commercial instrument,

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the Geonics EM-38, to measure rice soilproperties in our precision farmingexperimental sites (Fig. 6) as well as infarmers’ fields. The distribution of the EMreadings was consistent with field drainage.

A mobilized soil conductivity assessment(MSCA) system, with a mobile EM-38 sensorunit pulled by an ATV, equipped with alaptop computer and DGPS antenna, is underconstruction. We are trying to use thisequipment to map and/or categorize a widerange of physical and chemical soil properties.Our objective is to acquire quickly andaccurately site-specific management informationfor small fields.

Current research shows that there is apoor correlation between soil available P andthe EMI reading. However, there is astatistically significant relationship between theEMI value and the level of exchangeable soilK (Fig. 7). This suggests that a soil K map

could be made, calculated on the basis of aregression equation between the EM sensorreading and observed exchangeable soil K.

Specialized software, the ESAP-95(Version 2.01R) (Lesch et al. 2000) was usedto generate optimal sampling designs fromconductivity survey information. The spatialresponse surface (SRS) sampling designsoftware in the ESAP-95 is a useful packagewhich allows users to generate calibrationsample sizes of 6, 12, or 20 sites per field.Alternatively, users may adopt a customsampling design, using a special statisticaltechnique. Fig. 8 is an optimized sample sitemap for Plot 39 in our experimental farm atthe Taiwan Agricultural Research Institute.Given the location of our sample sites, onlysix samples had to be collected to representthe whole field. Further physical andchemical analysis can be carried out tounderstand the soil properties.

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*36: tobacco fertilizer; 39* most common rice fertilizer

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Variation in the levels of soil P and Kis different for every rice field. This isparticularly true when the fields belong todifferent farmers who have adopted differentfertilizer regimes (Fig. 9 and Fig. 10). Ourresults showed that the distribution of soil Pand K within a sampled field tends to followthe orientation of the drainage water.

Decision support systems to make field-specific fertilizer recommendations seemnecessary, since most farmers do not knowthe fertility of their soils. It would be helpfulif nitrogen applications could take yieldpotential into consideration. At present,chlorophyll meters are being used on ourexperimental farm to assess the nitrogen statusof rice from maximum tillering to the panicleinitiation stage of growth. Experiments havebeen conduced to determine critical meter

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values associated with 95% maximum ricegrain yield.

In Taiwan, most rice paddy fields arearound 0.3 ha in size, and can be treated as asingle management unit. If a field is largerthan 0.5 ha, a knowledge of variability in thedistribution of various nutrients might beuseful when variable-rate applications areconsidered. Fig. 11 shows the relativedistribution of different application rates ofP

2O

5 and K

2O in one field of 0.5 ha. Once

the target yield is decided, the desired ratio ofP and K, and the ideal compound fertilizeror straight nutrient fertilizers can be selected.Optimization strategies can be done with orwithout checking N levels.

Compound fertilizers have long been themost common nutrient input in Taiwan’s ricefields, because of their convenience inapplication and transportation compared tostraight nutrient fertilizers. Farmers arerecommended to use Compound Fertilizer No.39, which has a high P content, as a basalapplication for rice.

If more P is needed for each crop, it isadded as straight fertilizer (P

2O

5). The

remaining N and K is applied as a topdressing in the form of low-P compoundfertilizers.

Strictly speaking, there is not a wideenough range of compound fertilizers for ricegrowers. This may be a constraint inimplementing the technology of site-specificnutrient management.

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Many rice producers in Taiwan arecurrently facing low crop prices. These arelikely to fall even lower now that Taiwan hasjoined WTO. However, rice traditionally stillranks first in importance in crop production inTaiwan. Site-specific nutrient management isa new approach to production which mayreplace current uniform rate technology. Itoffers an opportunity to develop new andimproved fertilizer recommendations for ricefertilizer management.

Rice surplus problems in the past haveforced Taiwan’s rice growers to focus onimproved rice quality through cultivationtechniques. Site-specific or field-specificfertilizer management for rice is a good wayof helping farmers to apply fertilizer to their

fields rationally. Through the implementationof this technology, rice quality can beimproved and the environment protected.

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Chung, Sun-ok, Je-hoon Sun, K.A. Sudduth,S.T. Drummond and Byung-keun Hyun.2001. Spatial variability of yield,chlorophyll content, and soil properties inKorean rice paddy field. (http://www.fse.missouri.edu/mpac/pubs).

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Davis, J.G., R.N. Kitchen, K.A. Sudduth andS.T. Drummond. 1997. Usingelectromagnetic induction to characterizesoils. Better Crops 81: 6-8.

Day, D.T. and Y.J. Lin. 1992. Studies onthe amount and method of fertilizerapplication in paddy field in TaichungDistrict. I. The amount and frequency offertilizer application in paddy fields.Taichung DAIS Res. Bulletin 35: 33-40.

Geonics Limited. 1999. EM-38 GroundConductivity Meter Operation Manual.Ontario, Canada.

Griffin, T.W., J.S. Popp and D.V. Buland.2001. Economics of variable rateapplications of phosphorus on a rice andsoybean rotation in Arkansas. http://web.extension.uiuc.edu/macombcenter/F B M & M / F a c t % 2 0 S h e e t s /vrtgrifpopbul.PDF.

Guo, H.Y., T.S. Liu, C.L. Chu and C.C. Liu.1999. Chapter 4. Application of soilinformation. In: Crop RationalFertilization Technique, Lin et al. (Eds.).Society of Sustainable Agriculture,Taichung, Taiwan, ROC, pp. 67-80.

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Crops in Taiwan. Council of Agriculture,ROC. 293 pp.

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Lin, M.L. 2001. Fertilizer use by crop forthe various agro-ecological zones in

Taiwan. 67 pp. (Paper submitted to FAOfor web-publication, in press).

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