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Three soil test crop response (STCR) experiments were conducted with maize, soybean and rice during 2004–2006 at the Soil Science Division of the ICAR Research Complex for NEH Region, Umiam, Meghalaya. Four fertility-gradient strips were developed for each crop during the first year. Grain and straw samples were collected at harvest and analysed for nitrogen (N), phosphorus (P) and potassium (K) concentrations, and total nutrient uptake was calculated. Soil samples were also analysed for available N, P and K. The resulting soil-test and crop-response information was used to develop fertilizer adjustment equations for targeted yields of rice, maize and soybean. Follow-up trials were conducted in a selected village field using fertilizer doses calculated from the target-yield equations and soil-test values. The developed equations provide a quantitative basis for adjusting fertilizer application according to soil fertility status and desired yield targets. The approach can support balanced and efficient fertilizer use and improve the precision of fertilizer recommendations under the soil and crop conditions of Meghalaya.
Keywords: soil test crop response; STCR; fertilizer prescription; target yield; soil fertility; rice; maize; Meghalaya; soybean; soiltestcropresponse; fertilizerprescription; targetyield; soilfertility
Fertilizer management is a major determinant of crop productivity and long-term soil fertility. Conventional blanket fertilizer recommendations may not adequately account for variation in soil fertility, crop requirements and local growing conditions. Soiltestcropresponse(STCR)correlationsestablish quantitativerelationshipsbetweensoil-testnutrient status, fertilizer application and crop response underfieldconditions. Suchrelationshipsprovidea scientificbasisfordevelopingcalibrationchartsand recommendingbalancedfertilizerdosesforspecified yieldtargets.
Awell-calibratedSTCRapproachenablesfertilizernutrientstobeappliedinappropriateamountsaccording tothenutrient-supplyingcapacityofthesoilandthe yield target of the crop. This can improve fertilizeruseefficiency,reduceunnecessaryfertilizerapplicationandsupportsustainablecropproduction. Rice, maizeandsoybeanareimportantcropsinMeghalaya, whereproductivitycanbeimprovedthroughbalanced andsoil-test-basednutrientmanagement.Thepresent studywasundertakentodevelopfertilizeradjustment equationsandreadyreckonersforrice,maizeandsoybeanusingSTCRexperimentsconductedatUmiam, Meghalaya. Theobjectivewastorelatesoil-testN,P and K status to fertilizer requirements for predetermined yield targets and thereby provide a practical basisforsite-specificfertilizerrecommendations.
Three STCR experiments were conducted on maize, soybeanandriceduring2004–2006attheexperimental blockoftheSoilScienceDivision,ICARResearchComplexforNEHRegion,Umiam,Meghalaya.Fourfertilitygradientstripsweredevelopedforeachcropduring thefirstyear.Theexperimentalsoilwasanalysedfor basicsoilpropertiesandexhaustivecropsweregrown tocreatefertilitygradients. Afterharvest, thestrips weresubdividedintosmallerplotsandthesoilofeach plotwasanalysedforavailableN,PandK.
During the second year, maize, soybean and rice were grown in the respective STCR plots. Fertilizer treatmentswereimposedacrossthefertilitygradients accordingtothetreatmentcombinations. Grainand strawyieldswererecordedatharvest.Grainandstraw sampleswerecollectedandprocessedforestimation of N, P and K concentrations. Total uptake of N, P −1 and K (kg ha ) was calculated from the nutrient concentrationsandcropyielddata.
Avillagefieldwasselectedforafollow-uptrial. Soil samplesfromtheselectedfieldwereanalysedforavailableN,PandKduringthethirdyear.Fertilizerdoses werecalculatedusingthetarget-yieldapproachand thefertilizeradjustmentequationsdevelopedforthe respectivecrops.Theresultingrecommendationswere usedforthefollow-uptrial.
Theaccuracyoffertilizerrecommendationsdepends ontherepresentativenessofthesoilsampleusedfor calibrationandrecommendation.Soilpropertiescan varyspatiallybecauseofsoil-formingprocesses,erosion,nutrientaccumulationorloss,andmanagement practicessuchastillage,fertilization,cropselection andirrigation. Therefore,appropriatesoilsampling is essential for reliable fertilizer recommendations. Basedonsoil-testnutrientstatus,soilsweregrouped into low, medium and high fertility categories, and readyreckonerswerepreparedforspecifiedcrop-yield targets.
Thefertilizeradjustmentequationsdevelopedforrice, maizeandsoybeanarepresentedbelow.Intheseequations,F-N,F-P2O5 andF-K2OdenotefertilizerN,P2O5 andK2O,respectively; S-N,S-PandS-KdenotesoiltestN,PandKinelementalform;andTdenotesthe −1 predeterminedcrop-yieldtarget(qha ).
Table 1. Fertilizeradjustmentequationsforrice,maize andsoybean
FN = 2.82 × T − 0.13 × SN Rice FP2O5 = 1.88 × T − 0.08 × SP FK2O = 1.69 × T − 0.07 × SK FN = 1.99 × T − 0.11 × SN Maize FP2O5 = 1.49 × T − 0.11 × SP FK2O = 0.83 × T − 0.06 × SK FN = 1.81 × T − 0.06 × SN Soybean FP2O5 = 5.42 × T − 4.33 × SP FK2O = 4.51 × T − 0.21 × SK
TheSTCRexperimentsconductedonrice,maizeand soybeangeneratedquantitativerelationshipsbetween soil-test nutrient status, fertilizer application and cropyieldtarget.Thefertilizerprescriptionequations
10 15.2 18 9.9 20 43.4 36.8 26.8 30 71.6 55.6 43.7 40 99.8 74.4 60.6 50 128 93.2 77.5
Table 3. ReadyreckonerforfertilizerapplicationtomaizebasedonsoilN,PandKfertilitystatus
10 8.9 13.8 2.3 None 12.7 None None 12.15 None 20 28.8 28.7 10.6 30 48.7 43.6 18.9 40 68.6 58.5 27.2 50 88.5 73.4 35.5
developedforthethreecropsshowedthatfertilizer requirements were influenced by both the desired yieldtargetandtheavailablenutrientstatusofthesoil. Forrice,thefertilizerrequirementswereestimatedas FN = 2.82T − 0.13SN, FP2O5 = 1.88T − 0.08SP ,and FK2O = 1.69T − 0.07SK .Similarly,equationsdevelopedformaizewere FN = 1.99T − 0.11SN, FP2O5 = 1.49T − 0.11SP , and FK2O = 0.83T − 0.06SK. For soybean, the corresponding equations were FN = 1.81T − 0.06SN, FP2O5 = 5.42T − 4.33SP , and FK2O = 4.51T − 0.21SK. These equations demonstrate that fertilizer requirements can be adjustedaccordingtosoilnutrient-supplyingcapacity andthetargetedyield.Theequationsarepresentedin themanuscriptsource.
Thereadyreckonersdevelopedfromthefertilizerprescriptionequationsindicatedsubstantialdifferences infertilizerrequirementsamonglow-,medium-and high-fertilitysoils.Foragivenyieldtarget,fertilizerrequirementsgenerallydeclinedwithincreasingsoil-test nutrientavailability.Forrice,thecalculatedfertilizer requirementsincreasedprogressivelywiththeyield −1 targetfrom10to50qha . Similartrendswereobservedformaizeandsoybean. Thereadyreckoners thereforeprovideapracticalmeansoftranslatingsoiltestvaluesandyieldtargetsintocrop-specificfertilizer recommendations.
Thedevelopedreckonerfurtherdemonstratedtheeffectofsoil-testnutrientstatusonfertilizerrequirement for specific yield targets. In maize, for example, increasingsoil-testN,PandKlevelsresultedinprogressivelylowerfertilizerrequirementsforthespecified
N P2O5 K2O N P2O5 K2O N P2O5 K2O None 17.2 2.9 None 16.8 None 23.9 36 19.8 None 35.6 12.8 52.1 54.8 36.7 19.6 54.4 29.7 80.3 73.6 53.6 47.8 73.2 46.6 108.5 92.4 70.5 76 92 63.5
N P2O5 K2O N P2O5 K2O N P2O5 K2O
12.3 27.6 4.6 None 27.05 None 32.2 42.5 12.9 4.7 41.95 6.9 52.1 57.4 21.2 24.6 56.85 15.2 72.0 72.3 29.5 44.5 71.75 23.5
yieldtargets.Thisconfirmstheimportanceofaccountingfortheindigenousnutrient-supplyingcapacityof soilwhendeterminingfertilizerdoses.
TheresultsindicatethatSTCR-basedfertilizerrecommendations can provide a more precise alternative to uniform fertilizer application. By integrating soil fertilitystatuswithcropyieldtargets,thedeveloped equationsandreadyreckonerscanfacilitatebalanced nutrientapplicationandimprovetheefficiencyofappliedfertilizers. Thesourcemanuscriptalsoemphasizesthatappropriatesoilsamplingandsuitabletiming,methodanddoseoffertilizerapplicationareessentialforachievinghighernutrient-useefficiency.
TheSTCRapproachdevelopedinthisstudyprovides aquantitativeframeworkforintegratingsoilnutrientsupplyingcapacitywithcropnutrientrequirements. Thefertilizeradjustmentequationsshowthattherequiredfertilizerdosechangeswithboththedesired yieldtargetandthesoil-teststatusoftherespective nutrient.Consequently,thesameyieldtargetdoesnot necessarilyrequirethesamefertilizerdoseinsoilswith differentfertilitylevels.Earliertheseresultsreported byBharamappanavaraetal. (2020),Brajendra,etal. (2020),Caon,andVargas,(2017),Gopaletal.(2014). Thereadyreckonersfurthertranslatetheequations into practical fertilizer recommendations for low-, medium-andhigh-fertilitysoils.Assoil-testnutrient availability increases, the fertilizer requirement generally decreases for a given yield target. This relationshipdemonstratesthevalueofsoiltestingin improvingtheprecisionoffertilizermanagementand avoidingunnecessarynutrientapplication.
5 3.05 None 1.55 10 12.1 10.9 24.1 15 21.15 38 46.65 20 30.2 65.1 69.2 25 39.25 92.2 91.75 Note:“None”indicatesthatnofertilizernutrientwasrequiredaccordingtothecorrespondingtarget-yield equationandsoil-testfertilityclass.
EarliertheseresultsreportedbyGorlapallietal.(2022), Kaleetal.(2021),Kaleetal.(2020),Parmaretal.(2022).
Theequationsandreadyreckonersdevelopedforrice, maize and soybean can therefore serve as decisionsupporttoolsforbalancedfertilizationundertheconditionsrepresentedbytheexperiments.Theirpractical usedependsonappropriatesoilsampling,correctinterpretationofsoil-testresultsandadoptionofsuitable fertilizersource,dose,timingandplacementpractices. EarliertheseresultsreportedbyRathodetal.(2021), Sahoo et al. (2022), Srilatha et al. (2019), Tuti et al. (2022).
STCR-basedfertilizeradjustmentequationsweredeveloped for rice, maize and soybean using soil-test values,cropnutrientuptakeandtargeted-yieldrelationshipsestablishedunderfieldconditionsatUmiam, Meghalaya. Theresultingequationsandreadyreckonersprovideascientificbasisforadjustingfertilizer dosesaccordingtosoilfertilitystatusandyieldtargets. Adoptionofthesesoil-test-basedrecommendations canpromotebalancedfertilizeruse,improvenutrientuseefficiencyandsupportsustainablecropproduction.Accuratesoilsamplingandappropriatefertilizer applicationmethods,timinganddosesareessential forrealizingthebenefitsoftheSTCRapproach.