THE DOUBTFUL UTILITY OF PRESENT-DAY FIELD EXPERIMENTATION AND OTHER DETERMINATIONS INVOLVING SOIL-PLANT INTERACTIONS

8/13/2019 THE DOUBTFUL UTILITY OF PRESENT-DAY FIELD EXPERIMENTATION AND OTHER DETERMINATIONS INVOLVING SOIL-P

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Reprinted/rom SOILS ND FERTILIZERS Vol XXIII I960 307-310.

THE DOUBTFUL UTILITY OF PRESENT-DAY FIELD EXPERIMENTATION AND OTHER DETERMINATIONS INVOLVINGSOIL-PLANT INTERACTIONSby

N COLLIS-GEORGE AND B G DAVEY(School of Agriculture, University of Sydney, N.S.W.)

SUMMARYt is suggested, that since the influence of soil physical andm i c r o ~ m e t c o r o l o g i c l factors is known to be of great significance in determining the biological response of plants, thetime is now appropriate to restrict the number of conventional field experiments and replace some of them withcompletely instrumented expenments. Until completedescriptions of experiments arc available, the quantitativeimportance of environment and its interaction with fertilizerand cultivation practices cannot be determined. With suchinformation a limited number of field trials would yield moreupplicuble information than the urge number of uninstrumented trials now in existence.The argument is extended to I) the limited applicabilityof {lOt and glasshouse triuls; 2) the variation betweenreplicates in field trials as an uid to soil science; 3) thelimited utilization of soil surveys; 4) the poor correlationbetween arbitrary soil extracts und field responses; 5) themisuse of a common test species for assessing comparativesoil fertility in several regions; 6) the poor correlationbetween plant analyses and soil deficiencies.

The era of field experimentation, which began in1834 when J. B. Boussingault set up the first fieldexperiments at Bechelbonn, Alsace, was placed ona modern scientific basis by Liebig's report of 1840.The first field experiments in the form used to-daywere established by Lawes and Gilbert at Rothamsted in 1843. Since then the field experimentalisthas sought for and has confirmed the importance ofthe essential elements in influencing the productionof crops in the field. However, a great deal of theevidence for the necessity of specific nutrientelements has arisen from investigations in thelaboratory and not from field experiments (evenLiebig's startling discoveries of the importance ofN P and Kin the field were based on strong circumstantial evidence available prior to his experimentation). The application of the results of field trialsled to large increases in agricultural production,and the conversion of formerly unproductive ormarginal areas into useful agricultural land.

and have generaliy made the difference betweennegligible and economic production.By comparison, the results of most field experiments do not fall into such a category. Results offield trials vary from year to year, and although astatistical analysis may show a significant trend,as a consequence of one or more treatments, itdoes not give an invariable quantitative responseto any one treatment. Often field experiments canshow a qualitative difference in type of responsefrom season to season.t has become common practice to persist witha trial for a number of years in order to obtain astatistical "'average" result in an attempt to overcomethe unavoidable seasonal variability associated withfield work. Statistical evidence shows that from20 to 25 . in the best circumstances, of the totalvariation is associated with experimental error.The most modern techniques of experimentationhave not reduced this error term.

All experimentalists are aware of the importanceof season in determining their results, yet it isuncommon for them to define the meteorologicalenvironment, even by such modest means as theStevenson screen and rain gauge, during the progress of the trial. The transference of routinemeteorological data from a central station and theirapplication to experimental sites are unlikely to besatisfactory even when the aspect and situationsare similar. Yet, from a survey of the literature orby simple experiment, it can be quickly ascertainedthat moisture content of the soil, soil temperatureand the micro-meteorological factors greatly influence the behaviour of a plant. The uptake ofphosphorus, for example, is certainly dependent onsoil-moisture content, root temperature and solarradiation, and probably also on the relativehumidity gradient at the leaf surface. The yield ofcotton has been shown to be largely a function ofI t is significant that all of the biological responses the quantity and availability of soil moisture, andto fertilizer or cultural ameliorations which have n the production of pastures the response tobeen adopted into agricultural practice have been nitrogen fertilizers is determined by air temperatureas a consequence of very marked field-trial responses and solar radiation.

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The number of physical variables (soil and micrometeorological) known to control biological r e ~sponses seems to be expanding, whilst the totalnumber of chemical nutrients seems now to havebeen reached. The time is perhaps opportune toinvestigate the reasons for the variations encountered in soil-plant trials, and since methods are nowavailable for measuring many physical soil andmeteorological parameters it should be possibleeither to eliminate part of the error n field trials oreliminate those soil and climatic parameters inconsequential to plant performance.

The number of biological parameters which havebeen measured n field trials has been in its turnlimited, and comparison of grain and straw responses for wheat show that it is very dangerousto translate results from one wheat crop to anothereven if the soil and c r o ~ e n v i r o n m e n t are constant.Responses to applied nutrients undoubtedly varywith the parameter measured, for example theresponse to nitrogen in lettuce is more marked ona wet-weight than on a dry-weight basis. Subtlerdifferences occur when parameters involving consumer quality (and hence economic returns) areconsidered. In the long term, to obtain maximumuseful information from a field trial, it is not sufficient to limit the measured biological parametersto field weight or even to o v e n ~ d r y weight.

On the basis of the preceding two paragraphs, itcould be said that if more environmental parameters and more biological parameters wererecorded, fewer tria1s could be carried out with theavailable resources. t is one purpose of this paperto suggest that it is now time to stop the majorityof the "unrecorded" field trials.

The average trial, when analysed, yields thefollowing type of information: On site A, on soil B,with biological variety C using biological responseparameter D, from the years E to F there was astatistical average response G H for a certaintreatment." The definitions of A and B are notnecessarily unambiguous, and the economist maycomplain that there are not enough treatments toallow him to produce a production curve Theinformation yielded by this trial could only berigorously applied to some other site where thesequence of climate and crops had been identicaland where the soil parameter of consequence to thecrop are the same. The chances of such coincidenceand hence of quantitative applicability are remote.

Unless there is a deficiency, which is so markedthat it virtually prohibits growth, for example, traceelements in the 90-Mile Desert of South Australia,or the need for a basic dressing of phosphate onmost Australian soils, there hardly seems any needfor the infonnation given by most trials since itdoes not allow logical quantitative conclusions to.

be drawn about future trial responses. s thingsstand, when once one trial in an area on one soilbas been completed, it either shows a deficiency somarked that no land user can ignore it, regardlessof seasonal changes, or it shows marginal responseswhich the trial organizers cannot be sure willrepeated qualitatively, but do know are unlikely tobe repeated quantitatively in say, the next ten years.In either case, there would seem to be no need forsuccessive trials: in the first case, the answer iscomplete; in the second case it is uninterpretablesince no one as yet can quantitatively explainannual variations when "ail" the infonnation isbefore him and the series of annual trials concluded,

These remarks are not so stringently applicableto those trials whose object is to find the cumulativeor residual, effects of treatments on one site. Bufeven in these circwnstances there seems to be onlya weak case for persisting with the trial when themagnitude of the variation bet\veen treatments is ofthe same order as the variation in any one treatmentdue to seasonal variables.

The time has come to conduct far fewer trialsinvolving soil-plant interactions, and, in particular,almost to eliminate the large number of trials,which in some cases both in their design and in themethods have been repeated annually on one siteand are budgeted for almost indefinitely.In the history of fertilizer and soil-plant interaction trials each major discovery has caused a very

careful scrutiny of the results and methods used inthe earlier work. For instance, the discovery of theimportance of the rhizobia] strain and molybdenumin nitrogen fixation, and then later of the effect ofneutralized superphosphate in obtaining effectivenodulation in the field on acid soils, led to morecareful control in new field experiments, since theolder trials were uncontrolled in these respects. Afurther purpose of this paper is to claim that thereis now sufficient evidence concerning soil-plantinteractions as affected by environmental factors ofsoil and m i c r o ~ c l i m a t e to suppose that Jack ofrecorded information is preventing the interpretationof the results obtained in most "uncontrolled . fieldtrials, and that a new style of experimentation isneeded.

f the premise of the importance of the environmental factors in soil-plant interactions is accepted,several subsidiary but important conclusions can bedeveloped concerning other aspects of soil-plantrelationships. (Environment is used in its widestsense to include all soil physical and micro-meteorological factors which can influence biologicalresponse.)I) The limited applicability o pot and glasshousetrials Glasshouse trials, using pots and culture

*-Botanists, in general, have long accepted the consequences of environment on biological response in their thinking, butonly recently have had the techniques to estimate these. Many agricultural experimentalists and some biometridans seemto have ignored or minimized these consequences.


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are used w i d ~ l y as i n d i c ~ t o r s of soilility. The results are mterpretable m the case ofwhich are almost growth-restricting.application of glasshouse results in toto,is a hazardous procedure. Our hypothesisto the conclusion that the general transferencesuch results to field behaviour would be possiblerelationship of biological responses to environof thequantitatively. t is unlikely that the transwill be accomplished for some time. To

perhaps never be accomplished other than bycorrelation, but environmental controlsneed to be included in this correlation.he variation between replicates blocks) iutrials as an aid to soil science. In glasshousecare is taken to ensure uniform soil and, inaU

it is to be expected that thewill be much less than infield. When analysis of field trials has shown soilof treatments,of experimentalists has beennot invalidate the statisticaldifferences between treatments. Thisin detail and to lay out either aor a physically described trial,find those soil properties contributing to theor subBearing in mind that the original soil was

its superficial uniformity,ofnot relevant to crop perforThe limited utility of soil surveys-except in theof coutrolled or relativelyIt is a common experience:find different soils in the soil-survey sense)

of non-distinguishable soils (again in theofThis suggests, that, until the criteria control

of maturity at which the plant isbe ofIn regions, where the environment isor where the environmentin irrigation areas,rif identifying poor andbut generally this will be done bynot vice versa.

responses, so the relationship between arbitraryextracts, whether chemical or microbiological, andfield trials will be even more tenuous unless the fieldenvironment remains sensibly constant. The correlations between arbitrary extracts and pot trialswhere there is no water stress is always found to behigher than in the field where water is uncontrolled.The successful correlation, in Northern Europe

and New Zealand, between extracts and fieldresponses is almost certainly connected with thecomparatively high degree of reliability in rainfall,and the fact that some crops are virtually grown atfield-capacity moisture content for a large part oftheir life cycle.(5) he misuse ofa common test species for assessingcomparative soil fertility in several regions. A planttype chosen for its physiological vigour in a certainenvironment will be able to detect differencesbetween soils in that optimum environment. If theenvironment is significantly altered from theoptimum for expression of the genetic capabilitiesof the type, the principal response of the plant willbe to the change in its environment rather than tosoil treatment by fertilizers. Field trials conductedwith the same test species, in an attempt to comparethe fertility of soils in different regions, will morereflect the difference between the environments thanthe difference in field response to fertilizer treatments. There is no reason why there should be acommon measure of fertility; the soils of NorthernEurope, used for successful growing of rye, havea fair fertility as measured by rye grain in thatenvironment, but would have a poor fertility asmeasured by wheat.(6) T i t ~ poor correlatiOn between plant analyses andsoil deficiencies. The level of a given nutrientelement in a healthy field crop varies widely duringthe season and, furthermore, the magnitude of thevariation differs in different parts of the plant.Some of this variation can be correlated qualitatively with meteorological data, since plant physiologists are aware that bright , dull , cool orhot weather influences the production andpersistence of visual deficiency symptoms and thechemical constitution of plants. The majority ofcorrelations obtained between total plant analyses(or arbitrary extracts of plants) and field observations of productiveness or visual symptoms ofnutrient deficiencies have lacked precision, andattempts to set critical levels have given variablelimits of qualitative use in diagnosis.

ON LUSIONThe interpretation of many field trials involvingbiological parameters would appear, after a century,to have come to a stalemate for Jack of recordedcontrol or environmental data. The establishment of further field, fertilizer and soil-ameliorationThe poor correlation between arbitrary laboratory trials, glasshouse trials, assay procedures, andcts or micro-biological assays and field detailed soil surveys based an non-biological paraJust as glasshouse trials at near-optimum meters can only lead to a limited advance in ourure regimes are not easily related with field appreciation of soil-plant relationships. Until we

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of experimentationsoil sitewe cannot elucidate the imporof and the inter-relationship between these

t is not easy to define the cost of field trials asof officers who have other duties asas those concerned with trials are involvedor in laboratories andis no doubt that n u s t r ~ J i a alone

the total annual charge is in excess of A1 million:and our argument indicates that the majority of tbinformation so obtained is either already known ornot capable of quantitative application because oflack of data to interpret it.This analysis bas of necessity been limited to thegeneral field of soil science and acknowledgmentmust be made to the many agricultural scientists.who have helped to crysta1Iize the opinions expressedhere.

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THE DOUBTFUL UTILITY OF PRESENT-DAY FIELD EXPERIMENTATION AND OTHER DETERMINATIONS INVOLVING SOIL-PLANT INTERACTIONS