Leaf analysis as a means of assessing the nutrient status of deciduous fruit trees and vines in the Western Cape Province

[摘要] OBJECTIVE.High economic production has ever been the aim and aspirationof the agriculturist and no less that of the fruit farmer. Instriving towards this aim the latter has for a long time been ata disadvantage with regard to control of his nutritional programme.Even on naturally fertile soil, the question continually arises asto what the correct fertilizer treatment should be to maintain highproductivity and how such a decision can be arrived at. A satisfactoryanswer to these questions could have been obtained fromfertilizer trials if it was not such a difficult matter, in viewof the extensive and long-term nature of such trials with fruittrees, to establish a sufficient number for each fruit species ondifferent soil types and under different climatic conditions.Efforts to find a new approach to the problem have turnedattention to the plant itself and its chemical make-up as affordingthe best index of its nutritional requirements. Intensive work inthis direction has resulted in the evolution of a new tool inagriculture, the technique of diagnostic leaf analysis or 1Toliardiagnosis as originally proposed by Lagatu and Maume in Franceand Thomas in u.s.A. A review of the literature is presentedindicating the prodigous amount of research which has been appliedto studies of the relationship between plant response and nutrientsupply in terms of plant composition. Agriculturists have beenquick to recognize the potentialities of leaf analysis as a practicalguide in nutritional problems and advisory services basedon foliar analysis have already been established for certain cropsoverseas.The experimental basis for formulating such a scheme fordeciduous fruit in the Western Cape Province is provided by thefactual evidence presented in this thesis.THE TECHNIQUE.The technique of diagnostic leaf analysis comprises samplingof leaves, preparation of sample for analysis and the analysisitself followed by interpretation of the analytical results bycomparison with previously determined nutritional standards.Numerous factors were found to influence the final compositionof the leaf sample as determined by analysis, such that strictadherence to a standardized procedure through all phases ofsampling and preparation of leaf samples for analysis is requiredto eliminate or reduce errors likely to cause misleading interpretations.Experimental data are presented suggesting how theleaf sample should be selected on a tree and how it should behandled, cleaned, dried, ground and stored to reduce sampling andother errors.The final procedure as adopted eliminates most of the potentialsources of experimental error but two unavoidable sources ofe~ror remain to be accounted for, that due to tree variation andseasonal effect. The variation in leaf composition from tree totree was found to be very considerable, so that aampling from alarge enough group of trees (6 to 10) to reduce the error involvedis essential in order to obtain leaf data which correctly reflectsthe nutrient status of the portion of the orchard concerned.Secondly, on the grounds of marked consistency found in differentfruit species as to seasonal and year to year variation in mineralnutrient concentration, correction factors have been formulatedand are suggested as a means of overcoming these sources of error.THEORETICAL BASIS.A diagnosis of the nutrient status in terms of the analyticalresults as finally determined is obtained by comparison of the datawith previously established leaf composition standards of referenceand by correct interpretation of the deviations from these standards. The theoretical basis for setting up these index values isdiscussed. The criterion used is based on the concept of OptimumValues which aaequately integrates the known relationships betweenplant response and nutrient supply in terms of internal nutrientconcentration. A modification of this concept is proposed to theeffect that for maximum growth and yield there exists an optimumrange of nutrient concentrations with upper and lower limits foreach of the functional elements, and that within this range theinterrelationship between the individual nutrient elements is alsooptimal.Since no local fertilize~ trials with deciduous fruit treesare available and only one for grapes, data from highly productiveplants in commercial orchards and vineyards were used to determinethe upper and lower limits of the optimum range, on the followingpremise. If leaf analysis data are available from a sufficientnumber of high performance orchards in different localities representinga wide range of nutrient supply and environment, thehighest and lowest values obtained may be considered to representa close approximation of the limits of the range required foroptimum performance. It is contended that index values obtainedin this way must be of practical value in assessing the nutrientstatus of fruit trees. It is further postulated that the lowerlimits for the micro-nutrients and even for magnesium may bejustifiably adjusted according to the concentration levels associatedwith symptom expression.INDEX VALUES.The necessary data for determining standards of leaf compositionwere obtained from leaf analysis surveys of orchards andvineyards and from a grape fertilizer experiment in the WesternCape Province. Visual symptoms of prevailing nutritional disordersare described (supplemented by photographic illustrations)and their relation to leaf composition indicated. Tentative index values have been determined on the basis indicated for eachfruit species, apple, pear, peach, apricot, plum, prune and grapes.These nutritional levels comprise upper and lower limits for thenutrients N, P, K, Ca, Mg 1 Mn 1 Fe and Cu, as well as the upperlimits for B and Na.DIAGNOSTIC INTERPRETATIONS.Assessment of the nutrient status in terms of these indexvalues suggests that many orchards and vineyards in the WesternCape Province, particularly prune, apricot and grapes, are sufferingfrom malnutrition in some form and are likely to show a markedresponse to nutritional treatment as suggested by foliar diagnosis.The use of diagnostic leaf analysis constitutes an importantadvance in dealing with orohard problems in that an immediatedecision is possible regarding nutrient status and related aspectssuch as selection of suitable sites for fertilizer trials andadjustment of the fertilizer programme.

[发布机构] Stellenbosch University