Evaluation of a Dynamic Simulation Model for Tomato Crop Growth and Development

A dynamic simulation model for tomato crop growth and development,TOMSIM, is evaluated. Potential crop growth and daily crop grossassimilation rate (P_gc,d) is computed by integration of leafassimilation rates over total crop leaf area throughout theday. Crop growth results fromP_gc,dminus maintenance respirationrate (R_m), multiplied by the conversion efficiency. Dry matterdistribution is simulated, based on the sink strength of theplant organs, which is quantified by their potential growthrate. Within the plant, individual fruit trusses and vegetativeunits (three leaves and stem internodes between two trusses)are distinguished. Sink strength of a truss or a vegetativeunit is described as a function of its developmental stage.In this paper, emphasis is on the interactions between the twosubmodels of, respectively, dry matter production and dry matterdistribution. Sensitivity analysis showed that global radiation,CO₂concentration, specific leaf area (SLA) and the developmentalstage of a vegetative unit at leaf pruning had a large influenceon crop growth rate, whereas temperature, number of fruits pertruss, sink strength of a vegetative unit and plant densitywere less important. Leaf area index (LAI) was very sensitiveto SLA and the developmental stage of a vegetative unit at leafpruning. Temperature did not influence the simulated R_m, asincreased respiration rate per unit of biomass at higher temperatureswas compensated by a decrease in biomass. The model was validatedfor four glasshouse experiments with plant density and fruitpruning treatments, and on data from two commercially growncrops. In general, measured and simulated crop growth ratesfrom 1 month after planting onwards agreed reasonably well,average overestimation being 12%. However, crop growth ratesin the first month after planting were overestimated by 52%on average. Final crop dry mass was overestimated by 0–31%,due to inaccurate simulation of LAI, resulting partly from inaccurateSLA prediction, which is especially important at low plant densityand in a young crop.Copyright 1999 Annals of Botany Company Crop growth, dry matter production, glasshouse, leaf area,Lycopersicon esculentum, partitioning, simulation model, tomato, TOMSIM.     

Growth Response of a Chrysanthemum Crop to the Environment. III, Effects of Radiation and Temperature on Dry Matter Partitioning and Photosynthesis

Vegetative crops of chrysanthemum were grown for 5 or 6 weekperiods in daylit assimilation chambers. Crop responses to differentradiation levels and temperatures were analysed into effectson dry matter partitioning, specific leaf area, leaf photosynthesisand canopy light interception. The percentage of newly formed dry matter partitioned to theleaves was almost constant, although with increasing radiationor decreasing temperature, a greater percentage of dry matterwas partitioned to stem tissue at the expense of root tissue.There was a positive correlation between the percentage of drymatter in shoot material and the overall carbon: dry matterratio. Canopy photosynthesis was analysed assuming identical behaviourfor all leaves in the crop. Leaf photochemical efficiency wasonly slightly affected by crop environment. The rate of grossphotosynthesis per unit leaf area at light saturation, P_A (max),increased with increasing radiation integral, but the same parameterexpressed per unit leaf dry matter, P_w (max) was almost unaffectedby growth radiation. In contrast, P_A (max) was hardly affectedby temperature but P_w (max) increased with increasing growthtemperature. This was because specific leaf area decreased withdecreasing temperature and increased with decreasing radiation.There was a positive correlation between canopy respirationintegral and photosynthesis integral, and despite a four-foldchange in crop mass during the experiments, the maintenancecomponent of canopy respiration remained small and constant. Canopy extinction coefficient showed no consistent variationwith radiation integral but was negatively correlated with temperature.This decrease in the efficiency of the canopy at interceptingradiation exactly cancelled the increase in specific carbonassimilation rate that occurred with increasing growth temperature,giving a growth rate depending solely on the incident lightlevel. Chrysanthemum, dry matter partitioning, photosynthesis, specific leaf area     

Influence of Sink-Source Interaction on Dry Matter Production in Tomato

Sink-source ratio in tomato was manipulated, in six glasshouseexperiments, by fruit pruning (trusses pruned to two to sevenfruits immediately after fruit set of each truss), truss pruning(removal of every other truss at anthesis) and truss pruningin plants with two shoots. Periodic destructive harvest wereconducted for about 100 d after flowering of the first truss.Dry matter production was not influenced by sink-source ratio,whereas dry matter distribution between fruits and vegetativeparts was greatly affected. The fraction of dry matter distributedto the fruits at the end of the fruit pruning experiments (F_fruits)could be described accurately as a saturation-type functionof number of fruits retained per truss (N_f): F_fruits = 0.660(l-e^-0.341N_f). Specific leaf area and internode length decreasedand plant leaf area increased when sink-source ratio was reduced.Removal of every other truss at anthesis did reduce dry matterpartitioning into the fruits, but it did not influence internodelength. Plant development (number of visible leaves at the endof the experiments) was not influenced by sink-source ratio.In four experiments some plants were pruned to one fruit pertruss. Final dry matter production was 8-24% lower for theseplants, compared with plants with more than one fruit per truss.This was, at least party, the result of less light interceptionby these plants, which had strongly curled leaves pointing downwards. Results indicate that effects of sink demand on dry matter productionper unit of intercepted radiation and probably on leaf photosyntheticrate in commercial tomato production can be ignored.Copyright1995, 1999 Academic Press Dry matter production, feedback control, glasshouse, growth analysis, Lycopersicon esculentum, pruning, sink demand, sink-source ratio, tomato     

Nitrogen Uptake and Plant Growth II. An Empirical Model of Vegetative Growth and Partitioning

An empirical model of vegetative plant growth is presented.The model is based on experimental data on Polygonum cuspidatum,which showed (1) that the partitioning of dry matter and nitrogenamong organs was linearly related to the nitrogen concentrationof the whole plant and (2) that leaf thickness was negativelycorrelated with leaf nitrogen concentration. The model properlydescribes the behaviour of plants. Steady-state solutions ofthe model give the relative growth rate, specific leaf weight,and partitioning of dry matter and nitrogen among organs withthe net assimilation rate and the specific absorption rate asenvironmental variables. The effect of nitrogen removal on drymatter and nitrogen partitioning was examined as non-steady-statedynamic solutions of the model. The model predicted not onlyreduced leaf growth and enhanced root growth but also a fluxof nitrogen from the leaf to the root, which agreed with theexperimental results. Mathematical model, partitioning of dry matter and nitrogen, plant nitrogen, relative growth rate, shoot: root ratio, specific leaf weight     

Potential Dry Matter and Water Import Rates in the Tomato Fruit in Relationship to Fruit Size

The tomato fruit was compared to a sphere with a radius R. Radialgrowth rates in the fruit (F_IW and F_ID) due to water importor to dry matter import, respectively, which are also the waterimport rate or dry matter import rate per unit surface areaof fruit, were calculated from two sets of published results.This data referred to fruits which swelled in such a way thatthe availability of assimilates had little effect on growth.Two varieties differentiated the two series of results and inone series, three trials were differentiated by the salinityof the nutrient solution. In all trials, it was found that F_IW and F_ID decreased whenR increased. Two phases were observed for F_IW: after a firstphase, F_IW decreased more quickly and almost linearly when Rincreased. F_ID was constant or decreased with respect to R.Except at the beginning of growth at the greatest salinity,there were clearly linear regressions between F_IW and F_ID suchas F_ID = aF_IW-b; where b was lower with higher salinity. Thechanges of the concentration of imported dry matter (F_ID/F_IWwere examined in terms of R and F_IW/R. The mechanisms controllingthe changes in F_IW and F_ID were discussed. The results suggestedfruit radius was an important parameter of these mechanisms.Thus, water import rate and dry matter import rate could eachbe considered to be the product of two factors: fruit surfacearea, which is directly dependent on fruit radius, and waterimport rate or dry matter import rate per unit of fruit surfacearea.Copyright 1993, 1999 Academic Press Dry matter, fruit growth, logistic model, sink size, tomato, water transfer     

Use of the Expolinear Growth Model to Analyse the Growth of Faba bean, Peas and Lentils at Three Densities: Fitting the Model

The expolinear equation for crop growth (Goudriaan and MonteithAnnalsof Botany66: 695–701, 1990) was fitted to measurementsof above ground dry weight made on two cultivars of each ofthree species, faba bean (Vicia fabaL.), peas (Pisum sativumL.)and lentils (Lens culinarsMedic.), each grown at three densitiesat the University of Reading, UK in 1992 and 1993. The expolinearequation fitted the data well but required frequent samplingto obtain good estimates of the parameters. The equation hasthree parameters,R_mthe maximum relative growth rate,C_ma maximumcrop growth rate, andt_bthe time at which the crop effectivelyreaches a linear phase of growth.R_mdid not differ between densities,cultivars or species but differed between years.C_mincreasedwith increased density and was lower for lentils than for fababeans or peas.t_bdecreased with increased density for faba beanbut not for the other species. Incorporating an extinction coefficientfor solar radiation and the maximum fraction of radiation interceptedenabled reasonably accurate time courses of leaf area indexto be derived, as suggested by Goudriaan (1994. In: MontiethJL, Scott RK, Unsworth MH, eds.Resource capture by crops. Nottingham:Nottingham University Press, 99–110).Copyright 1998 Annalsof Botany Company Expolinear equation, grain legumes, crop growth rate, crop density, relative growth rate, growth modelling, faba bean,Vicia fabaL., peas,Pisum sativumL., lentils,Lens culinarsMedic.     

Nitrogen Uptake and Plant Growth I. Effect of Nitrogen Removal on Growth of Polygonum cuspidatum

Polygonun cuspidatum was grown hydroponically to examine theeffect of nitrogen removal from the nutrient solution upon plantgrowth and the partitioning of dry matter and nitrogen amongorgans. Nitrogen removal reduced the growth rate mainly dueto the reduced growth of leaf area. Accelerated root growthwas observed only in plants which earlier had received highlevels of nitrogen. Nitrogen removal caused almost exclusiveallocation of available nitrogen to root growth. Nitrogen fluxfrom the shoot to the root occurred in plants which had receivedlow nitrogen. Not only was net assimilation rate (NAR) littleaffected by nitrogen removal, but it also was not correlatedwith the concentration of leaf nitrogen on an area basis. Light-saturatedCO₂ exchange rate (CER) was highly correlated with the concentrationof leaf nitrogen. Nitrogen use efficiency (NUE) in CER (CERdivided by leaf nitrogen) remained constant against leaf nitrogen,indicating efficient use of nitrogen under light saturation,while NUE in terms of NAR decreased with higher concentrationof leaf nitrogen. Polygonum cuspidatum Sieb. et Zuce., CO₂ exchange rate, growth analysis, leaf nitrogen, net assimilation rate, nitrogen use efficiency, partitioning of dry matter and nitrogen     

Growth Analysis of Solution Culture-grown Winter Rye, Wheat and Triticale at Different Relative Rates of Nitrogen Supply

At low nitrogen (N) supply, it is well known that rye has ahigher biomass production than wheat. This study investigateswhether these species differences can be explained by differencesin dry matter and nitrogen partitioning, specific leaf area,specific root length and net assimilation rate, which determineboth N acquisition and carbon assimilation during vegetativegrowth. Winter rye (Secale cereale L.), wheat (Triticum aestivumL.) and triticale (X Triticosecale) were grown in solution cultureat relative addition rates (R_N) of nitrate-N supply rangingfrom 0.03–0.18 d^-1and at non-limiting N supply under controlledconditions. The relative growth rate (R_W) was closely equalto R_Nin the range 0.03–0.15 d^-1. The maximalR_W at non-limitingnitrate nutrition was approx. 0.18 d^-1. The biomass allocationto the roots showed a considerable plasticity but did not differbetween species. There were no interspecific differences ineither net assimilation rate or specific leaf area. Higher accumulationof N in the plant, despite the same relative growth rate atnon-limiting N supplies, suggests that rye has a greater abilityto accumulate reserves of nitrogen. Rye had a higher specificroot length over a wide range of sub-optimal N rates than wheat,especially at extreme N deficiency (R_N=0.03–0.06 d^-1).Triticale had a similar specific root length as that of wheatbut had the ability to accumulate N to the same amount as ryeunder conditions of free N access. It is concluded that thebetter adaptation of rye to low N availability compared to wheatis related to higher specific root length in rye. Additionally,the greater ability to accumulate nitrogen under conditionsof free N access for rye and triticale compared to wheat maybe useful for subsequent N utilization during plant growth.In general, species differences are explained by growth componentsresponsible for nitrogen acquisition rather than carbon assimilation.Copyright 1999 Annals of Botany Company Growth analysis, nitrogen, nitrogen productivity, partitioning, specific root length, Secale cereale L.,Triticum aestivum L., X Triticosecale, winter rye, winter wheat, winter triticale.     

Growth and Biomass Allocation, with Varying Nitrogen Availability, of Near-isogenic Pea Lines with Differing Foliage Structure

The single-gene mutation afila in pea (Pisum sativum L.) resultsin the replacement of proximal leaflets with branched tendrils,thereby reducing leaf area. This study investigated whethertheafila line could adjust biomass partitioning when exposedto varying nutrient regimes, to compensate for reduced leafarea, compared with wild-type plants. Wild-type and afila near-isogeniclines were grown in solution culture with nitrate-N added toinitially N-starved seedlings at relative addition rates (R_N)of 0.06, 0.12, 0.15 and 0.50 d^-1. The relative growth rate (R_W)of the whole plants closely matched R_Nat 0.06 and 0.12 d^-1,but higher R_Nresulted in a slightly higher growth rate. At agiven R_N, the wild-type line had lower plant nitrogen statusthan the afila line. R_Wof the roots of the afila line was lessthan R_Wof the roots of the wild-type at the three higher ratesof N supply despite a greater accumulation of N in the rootsof the afila plants. Consequently, plant nitrogen productivity(growth rate per unit nitrogen) was lower for afila. Dry matterallocation was strongly influenced by nitrogen status, but nodifferences in shoot–root dry matter allocation were foundbetween wild-type and afila with the same plant N status. Theseresults imply that decreased leaf area as a result of the single-genemutation afila affects dry matter allocation, but only accordingto its effect on the nitrogen status. Copyright 2000 Annalsof Botany Company Pisum sativum, pea, nitrogen limitation, growth, shoot–root allocation, relative growth rate, nitrogen productivity, isolines     

Nitrogen Deficiency in Small Closed Communities of S24 Ryegrass. I. Photosynthesis, Respiration, Dry Matter Production and Partition

Small communities of S24 ryegrass were grown under supplementarylights in a glasshouse at 20°C, and abundantly suppliedwith a complete nutrient solution containing 300 p.p.m. of nitrogen,until they had a leaf area index of 5 and fully interceptedthe light. Half were then given a solution containing only 3p.p.m. of nitrogen (LN) while the rest were kept at 300 p.p.m.(HN). The LN plants had a rate of single leaf photosynthesis lowerthan that of the HN plants at all but the lowest light intensities(33 per cent lower at the saturating irradiance of 170 W m^–2).Similarly, the LN communities had rates of canopy gross photosynthesis(P_sc) markedly lower than those of the HN communities. A comparisonof the observed rates of P_sc with those predicted by a mathematicalmodel of canopy photosynthesis indicated that it was the effectof nitrogen on single leaf photosynthesis, rather than differencesbetween the communities in leaf area, which led to the observeddifferences in P_sc. The superiority of the HN communities in terms of P_sc was partlyoffset by a higher rate of respiration so that they only exceededthe LN communities in terms of canopy net photosynthesis atirradiances in excess of 180 W m_–2, and produced only15 per cent more total dry matter. Nevertheless, the HN plantsdirected less of that dry matter into root and more into topsso that they came to possess twice the weight of live laminae,and the HN communities twice the leaf area, of their nitrogendeficient counterparts. Lolium perenne, S24 ryegrass, photosynthesis, respiration, dry matter production and partition, nitrogen dekieacy     

Growth Response of a Chrysanthemum Crop to the Environment. II. A Mathematical Analysis Relating Photosynthesis and Growth

Vegetative crops of chrysanthemum were grown for 5 weeks inthree replicate daylit assimilation chambers. Weekly harvestswere made from each crop for growth analysis, and on seven occasionsduring the 5-week period continuous measurements of the netCO₂ exchange rate of each crop were made over a 24 h period.A semi-empirical model for canopy photosynthesis was fittedto these data. The photosynthesis model was then incorporatedinto a simple, dynamic growth model. Using fitted values ofthe canopy photosynthesis parameters, the daily total radiationintegrals, and the experimentally observed relationship betweenthe leaf area index and crop dry matter per unit ground area,the crop growth model was used to simulate growth over the 5-weekperiod. The predicted and measured crop dry weights were inclose agreement over the whole period.     

Transfer of Mass and Energy in a Cassava Community (Manihot esculenta Crantz cv. Cubana) 2. CO2 Exchange in a Savanna Climate

The energy balance approach was applied to calculate the CO₂flux above and within a cassava community, growing during asavanna wet season. Data of the response of CO₂ exchange todiurnal changes in the savanna environment were integrated toa growth analysis of the cassava crop. The carbon budget of the entire community was calculated atdifferent development stages. Results indicate that CO₂ uptakein cassava appears to follow a linear net radiation responsecurve, dependent on crop age. The maximum net CO₂ uptake decreasedfrom 0.195 MJ m^–2 day^–1 at maximum leaf area development(August) to 0.028 MJ m^–1 day-1 2 months later. These ratesrepresent 41 and 19 per cent gross assimilation. Data of energy conversion efficiency show that at a maximumleaf area development, the crop fixed 2.2 and 0.9 per cent Rtas gross (_g) and net photosynthesis (n) respectively. As theseason proceeded,n decreased to 0.1, whereas g decreased to0.7, which indicates that dry matter lost by respiration isone of the determining factors in the seasonal trend of efficiencychanges. The comparison of growth characteristics calculated for cv.Cubana, growing during consecutive years in the same experimentalsite, indicate that yearly variability in dry matter accumulationis due to the wide range of environmental conditions presentduring the savanna wet season. Operational factors acting depressivelyon the cassava carbon budget and affecting dry matter productionwere also analysed. Manihot esculenta Crantz, cassava, microclimate, carbon budget, carbon dioxide fluxes     

An Analysis of the Photosynthesis and Productivity of Vegetative Crops in the United Kingdom

The rate of total dry matter production of a vegetative crop,under optimal water and nutrient regimens is related to someleaf and canopy photosynthetic characteristics. Three leaf photosyntheticcharacteristics are examined in detail: the light utilizationefficiency at normal ambient CO₂ and O₂ concentrations, a, therate of light saturated photosynthesis per unit leaf area, F_max,and the ratio of the rates of photorespira tion and gross photosynthesis.The genetic variability in each of these characteristics issought from published data on a wide range of C₃ and C₄ planttypes. Within C₃ and C₄ plant types there are significant genetic differencesonly in F_max,, although differences exist between C₃ and C₄plants in the other two characteristics. The effects of thesedifferences on the rate total dry matter production are estimated,and it is concluded that there is no compelling evidence toindicate that improvements in total dry matter production rates,in the U.K., are likely to result from genetic manipulationof these characteristics in the existing range of plant material.     

Effect of Temperature and Nitrogen Supply on the Growth of Perennial Ryegrass and White Clover. 1. Carbon and Nitrogen Economies of Mixed Swards at Low Temperature

Simulated mixed swards of perennial ryegrass (Lolium perenneL. cv. S23) and white clover (Trifolium repens L. cv. S100)were grown from seed under a constant 10°C day/8°C nighttemperature regime and their growth, and carbon and nitrogeneconomies examined. The swards received a nutrient solution,every second day, which contained either high (220 µgg^–1) or low (40 µg g^–1) nitrate N. The High-N swards had rates of canopy photosynthesis and drymatter production (over the linear phase of growth) similarto those previously shown by mixed swards at high temperature.The Low-N swards grew more slowly; canopy photosynthesis, ata given LAI, was similar to that at High-N but lower LAI's weresustained. Clover increased its contribution to total carbonuptake and total dry weight throughout the period in the Low-Ntreatment and, despite the fact that grass took up most of theavailable nitrate, clover maintained a consistently higher Ncontent by virtue of N₂-fixation. At High-N, grass dominated throughout the measurement period.Earlier, when plants grew as spaced individuals, clover grewless well than grass, but once the canopy was closed it hada similar relative growth rate and thus maintained a steadyproportion of total sward dry weight. It is proposed that earlyin the development of the crop, leaf area production is thelimiting factor for growth, and that in this respect cloveris adversely affected by low temperature relative to grass.Later, as the LAI of the crop builds up, and the canopy becomesfully light intercepting, net canopy photosynthesis plays amore dominant role and here the higher photosynthetic rate perunit leaf area of the clover is crucial. Trifolium repens, white clover, Lolium perenne, perennial ryegrass, low temperature, nitrogen, photosynthesis     

Leaf Growth in Cotton (Gossypium hirsutum L.) 1. Growth in Area of Main-stem and Sympodial Leaves

A model is presented for growth of individual and successivemain-stem leaves of cotton, based on a series of indoor experimentsand data sets from the literature. Three variable parametersare used to describe individual leaf growth: relative growthrate of meristematic tissue (R¹), relative rate of approachof final area (R₂) and a ‘position parameter’ (t_0.5)which governs the transition from meristematic to extensiongrowth. Final area of a leaf does not occur in the model asa deterministic quantity but it is a result of the processesduring growth. The model generates successive mainstem leavesand sympodial leaves as an integrated system. Assimilate shortagesoccurring in the plant operate on R₁ leading to the characteristicchange of final leaf area along the mainstem. Gossypium hirsutumL., cotton, leaf growth, relative growth rate, meristematic tissue, extension growth, mathematical model     

Carbon and Nitrogen Assimilation by Vicia faba L. at Low Temperature: the Importance of Concentration and Form of Applied-N

Low temperature (6 C) growth was examined in two cultivarsof Vicia faba L. supplied with 4 and 20 mol m^–3 N as nitrateor urea. Both cultivars showed similar growth responses to increasedapplied-N concentration regardless of N-form. Total leaf areaincreased, as did root, stem and leaf dry weight, total carboncontent and total nitrogen content. In contrast to findingsat higher growth temperatures, 20 mol m^–3 urea-N gavesubstantially greater growth (all parameters measured) than20 mol m^–3 nitrate-N. The increased carbon content per plant associated with increasedapplied nitrate or urea concentration, or with urea in comparisonto nitrate, was due to a greater leaf area per plant for CO₂uptake and not an increased CO₂, uptake per unit area, carbon,chlorophyll or dry weight, all of which either remained constantor decreased. Nitrate reductase activity was substantial inplants given nitrate but negligible in plants given urea. Neitherfree nitrate nor free urea contributed greatly to nitrogen levelsin plant tissues. It is concluded that there is no evidence for a restrictionin nitrate reduction at 6 C, and it is likely that urea givesgreater growth than nitrate because of greater rates of uptake. Vicia faba, broad bean, low temperature growth, carbon assimilation, nitrogen assimilation     

Validation of a Photosynthesis Model through the Use of the CO2Balance of a Greenhouse Tomato Canopy

Several leaf photosynthesis models were developed from wellcontrolled experiments in growth chambers. However, only a fewhave been validated under greenhouse conditions for their quantitativeand qualitative adequacy. In this paper, rates of net photosynthesisfor a tomato crop (Lycopersicon esculentum Mill) were measuredin a semi-commercial greenhouse (615 m³) for a significant timeperiod. Concomitant measurements of climatic conditions andLAI were used for simulation of net photosynthesis using theTOMGRO model which integrates Acock's model for photosynthesiscalculations. From simulations and from sensitivity analysis,the prediction of net photosynthesis appeared to be very sensitiveto the quantum use efficiency. The Acock model with originalparameters underestimated the net photosynthesis rate, but anincrease in the quantum use efficiency by 10% gave a good fit.In an effort to generalize the validity of the model, a residualanalysis was performed and showed a systematic bias relatedto light intensity intercepted by the canopy. The Marquardtalgorithm was used to adjust our data to the model but did noteliminate residual heterogeneity of variance with new parametervalues. On the basis of collected data, the criteria of goodnessof fit used showed that the photosynthesis model is inadequatein describing the CO₂-balance of the greenhouse agrosystem.However, it was determined that it could be used as a submodelwithin a more complex model for predicting growth and development.Copyright 1999 Annals of Botany Company Greenhouse, CO₂-balance, photosynthesis, TOMGRO model, Acock's model, residuals, tomato Lycopersicon esculentum Mill.     

Effect of Defoliation During the Early Vegetative Phase and at Silking on Growth of Maize (Zea mays L.)

Two experiments were conducted in the glasshouse and in thefield to evaluate the effect of leaf loss on development, drymatter accumulation and yield of maize. In the glasshouse, defoliationtreatments were imposed on maize after 3 weeks of planting.Removing 2 or 3 leaves every 2 weeks affected plant height,days to tassel, root and shoot yield. The plant diameter androot:shoot ratio were not affected by defoliation. In the field experiment, six defoliation treatments were imposed7 days after 50 per cent silking. Defoliation of all leaveswas the most severe treatment on cob d. wt, dry matter accumulationin grains, weight of 100 test grains and yield. The effect ofremoving all leaves above the ear was not significantly differentfrom that of removing all leaves below the ear. The effect ofremoving half of the leaves above the ear was not differentfrom the control. Zea mays, vegetative growth, dry matter accumulation, yield, defoliation     

Variations with Age in Net Assimilation Rate and other Growth Attributes of Sugar-beet, Potato, and Barley in a Controlled Environment: With two Figures in the Text

Sugar-beet, potato, and barley plants were grown in a controlledenvironment, for periods of up to 10 weeks from sowing, witha light intensity of 1,8oo f.c. (4·9 cal./cm.²/hr.) anda temperature of 20° C. during the 18-hour photoperiod and15° C. during the dark period, to test whether net assimilationrate varied with age and differed between the three species. Net assimilation rate of all species based on leaf area (E_A)fell approximately linearly with time. During 5 weeks E_A ofsugar-beet decreased by only about 20 per cent. and E_A of potatodecreased by 50 per cent. E_A of barley remained approximatelyconstant for 4 weeks after sowing and was halved during thesubsequent 4 weeks. The average value of E_A for all times wasgreatest for sugarbeet and least for barley. Net assimilation rates based on leaf weight (E_W) and leaf N(E_N) decreased at about 15 per cent. of the initial value perweek for all species; this was similar to the mean rate of decreaseof E_A of potato and barley, but greater than that of E_A of sugar-beet.Mean values of E_W or E_N for potato and barley were similar andless than for sugar-beet. Relative growth rate (R_W), relative leaf growth-rate (R_A), andleaf-area ratio (F) fell with time at similar rates for allspecies. Average values of R_W decreased and of F increased inthe order sugar-beet, potato, barley. R_A was greatest for potatoand least for barley.