P.E.L. van der Putten

Simulation of wheat growth and development based on organ-level photosynthesis and assimilate allocation

Intimate relationships exist between form and function of plants, determining many processes governing their growth and development. However, in most crop simulation models that have been created to simulate plant growth and, for example, predict biomass production, plant structure has been neglected. In this study, a detailed simulation model of growth and development of spring wheat (Triticum aestivum) is presented, which integrates degree of tillering and canopy architecture with organ-level light interception, photosynthesis, and dry-matter partitioning. An existing spatially explicit 3D architectural model of wheat development was extended with routines for organ-level microclimate, photosynthesis, assimilate distribution within the plant structure according to organ demands, and organ growth and development. Outgrowth of tiller buds was made dependent on the ratio between assimilate supply and demand of the plants. Organ-level photosynthesis, biomass production, and bud outgrowth were simulated satisfactorily. However, to improve crop simulation results more efforts are needed mechanistically to model other major plant physiological processes such as nitrogen uptake and distribution, tiller death, and leaf senescence. Nevertheless, the work presented here is a significant step forwards towards a mechanistic functional-structural plant model, which integrates plant architecture with key plant processes.

Field observations on nitrogen catch crops. I. Potential and actual growth and nitrogen accumulation in relation to sowing date and crop species

In temperate climates with a precipitation surplus during autumn and winter, nitrogen catch crops can help to reduce nitrogen losses from cropping systems by absorbing nitrogen from the soil and transfer it to a following main crop. The actual and potential accumulation of dry matter and nitrogen in catch crops were studied in the field during four seasons with winter rye (Secale cereale) and forage rape (Brassica napus ssp. oleifera (Metzg.) Sinsk) or oil radish (Raphanus sativus spp. oleiferus (DC.) Metzg.). Sowing dates were end of August and three and six weeks later. Potential nitrogen accumulation, Y (g m-2), could be summarized with Y = 96 −0.34 X, where X is the day number in the year of the sowing date (range: late August till end of September). Species were compared in their performance, looking at differences in specific leaf area, leaf weight ratio, leaf area ratio, light extinction and persistence during frost. The rate of dry matter accumulation in intervals of 14 days appeared to be determined primarily by the amount of radiation intercepted. A regression, forced through the origin, gave as a common slope 1.12 g dry matter accumulated per MJ intercepted global radiation, irrespective of season, species, sowing date or nitrogen treatment (period from ca. day 250 to day 310). From this result the inference is made that leaf expansion is a key process, determining the performance of catch crop species under varying environmental conditions.

Field observations on nitrogen catch crops. II. Root length and root length distribution in relation to species and nitrogen supply.

Nitrogen catch crops help to reduce the loss of nitrogen from arable cropping systems during autumn and winter. The ability of catch crops to absorb nitrogen from the soil profile is affected by rate and depth of colonization of the soil by roots. The aim of the current work was to analyze total root length and root length density of catch crops in relation to above ground growth, nitrogen supply and crop species. In two field experiments roots were sampled with an auger. Experimental factors included crop species (winter rye, Secale cereale and forage rape, Brassica napus ssp. oleifera (Metzg.) Sinsk., or oil radish, Raphanus sativus spp. oleiferus (DC.) Metzg.), two sowing dates S1 and S2 (end of August and three weeks later) and two nitrogen treatments: N0, no nitrogen applied, and N1, nitrogen applied at non-limiting rate.The natural logarithm of the total root length, measured in the top 40 cm, L0–40 (km m-2), was linearly related to natural logarithm of the dry weight of the shoot, W (g m-2). There was no effect of species or sowing date on this relation. For a given W, N1 treatments showed lower values of L0–40 than N0 treatments. The decline in root length density, D (cm cm-3), with depth, X (cm), was described with the function ln D = ln D0 − qX, where D0 is the value of D at zero depth and q the linear coefficient. D0 was linearly related to L0–40, without effect of species, time of observation or N supply. The ratio D0/q, an estimate of the absolute root length, was 1.24 × L0–40.Together the relations enable estimates to be made of total root length and of root length distribution with depth using shoot dry weight of catch crops and its change with time as input. The generation of such estimates of root distribution is necessary for model studies in which the efficacy of catch crops to prevent N losses is evaluated in relation to sowing dates, distribution of N in the soil profile and the distribution of rainfall in the season.

Nutrient cycling in a cropping system with potato, spring wheat, sugar beet, oats and nitrogen catch crops. II. Effect of catch crops on nitrate leaching in autumn and winter

The Nitrate Directive of the European Union (EU) forces agriculture to reduce nitrate emission. The current study addressed nitrate emission and nitrate-N concentrations in leachate from cropping systems with and without the cultivation of catch crops (winter rye: Secale cereale L. and forage rape: Brassica napus ssp. oleifera (Metzg.) Sinksk). For this purpose, ceramic suction cups were used, installed at 80 cm below the soil surface. Soil water samples were extracted at intervals of ca 14 days over the course of three leaching seasons (September – February) in 1992–1995 on sandy soil in a crop rotation comprising potato (Solanum tuberosum L.), spring wheat (Triticum aestivum L.), sugar beet (Beta vulgaris L.) and oats (Avena sativa L.). Nitrate-N concentration was determined in the soil water samples. In a selection of samples several cations and anions were determined in order to analyze which cations primarily leach in combination with nitrate. The water flux at 80 cm depth was calculated with the SWAP model. Nitrate-N loss per interval was obtained by multiplying the measured nitrate-N concentration and the calculated flux. Accumulation over the season yielded the total nitrate-N leaching and the seasonal flux-weighted nitrate-N concentration in leachate. Among the cases studied, the total leaching of nitrate-N ranged between 30 and 140 kg ha–1. Over the leaching season, the flux-weighted nitrate-N concentration ranged between 5 and 25 mg L–1. Without catch crop cultivation, that concentration exceeded the EU nitrate-N standard (11.3 mg L–1) in all cases. Averaged for the current rotation, cultivation of catch crops would result in average nitrate-N concentrations in leachate near or below the EU nitrate standard. Nitrate-N concentrations correlated with calcium concentration and to a lesser extent with magnesium and potassium, indicating that these three ion species primarily leach in combination with nitrate. It is concluded that systematic inclusion of catch crops helps to decrease the nitrate-N concentration in leachate to values near or below the EU standard in arable rotations on sandy soils.

Plant development and leaf area production in contrasting cultivars of maize grown in a cool temperate environment in the field

Crop models need accurate simulation of the interdependent processes of crop development and leaf area production. Crop development proceeds according to genotype characteristics and environmental influences, specifically temperature and photoperiod. It can be partly described by thermal requirements for development intervals and coefficients that describe genotype adaptation. The objectives of this study were to (a) quantify (i) time of tassel initiation, tasselling and silking; (ii) thermal intervals for initiation, appearance and expansion of successive leaves (iii) thermal duration from initiation to tip appearance and from tip appearance to collar appearance, and (iv) leaf area and canopy cover as measured by leaf area index (LAI) in contrasting cultivars of maize grown in the field in a cool environment; and (b) relate these to plant characteristics and environmental variables, particularly temperature. For these purposes, three cultivars of maize were grown in three and four cultivars in two serial plantings from 18 April to 24 June in field experiments at Wageningen, The Netherlands, in 1997, and detailed data on crop development, leaf production and environmental variables were collected. The base temperature (Tb) for maize was confirmed as 8 degrees C, but thermal time calculation needs to be re-examined to explore a recovery period after chilling injury. Equations that relate foliar properties to total leaf number and ordinal leaf position were derived. Individual leaf area can be described by the modified bell curve, and differences in temporal increase in LAI were related to parameters of leaf initiation, appearance and expansion.

Nutrient cycling in a cropping system with potato, spring wheat, sugar beet, oats and nitrogen catch crops. I. Input and offtake of nitrogen, phosphorus and potassium

Nutrient balances, defined as the difference between input with manures, fertilizers and atmospheric deposition and offtake of nutrients with harvested products in arable cropping systems, need to be positive to compensate for unavoidable losses to the environment, but should be kept at the lowest possible level to minimize emissions or unnecessary accumulation of nutrients in the soil. Data from five consecutive years are reported from a long-term nutrient monitoring experiment with three replicates, managed comparably to conventional farming practice. There were four nutrient treatments (T1–T4). Treatment T1 received chemical fertilizer only. T2 received processed organic manure, supplying 50 per cent of the crop N-requirement, supplemented by chemical fertilizers. In treatments T1 and T2 the soil was bare during winter. In T3 and T4 the crops were fertilized as in T1 and T2, respectively, but nitrogen catch crops were grown in autumn and winter. Averaged over five years, the N-balances were 46 kg N ha-1 y-1 in T1 and T2 and 25 kg ha-1 y-1 in T3 and T4 (atmospheric deposition of 44 kg N ha-1y-1 included). Averaged over all treatments and years, the P-balance was 7 kg ha-1 y-1 and the K-balance -33 kg ha-1 y-1. The initially high soil fertility indices for both P and K declined over the experimental period. Catch crops and organic manure did not affect crop yields or nutrient balances, except that their combination in T4 resulted in 1.5 ton ha-1 extra dry matter yield of sugar beet roots. Between spring and harvest, potato and sugar beet showed positive N balances and the cereals negative N-balances. Sugar beet was the only crop with a positive K-balance. NPK concentrations in plant products were not systematically affected by treatments but varied considerably between seasons. At harvest, on average 63, 71, 75 and 112 kg N ha-1 (0–90 cm) were found after sugar beet, spring wheat, oats and potato, respectively. In November catch crops accumulated on average 39 kg N ha-1 after cereals and 33 and 5 kg ha-1 after potato and sugar beet, respectively. In March catch crops after the cereals contained 4 kg N ha-1 less than in autumn, but after potato and sugar beet N-accumulation in spring had increased to 49 and 29 ha N ha-1, respectively. In spring soil mineral N (0–90 cm) varied across years from 31 to 63 kg ha-1. The results indicate that compliance with a maximum excess of input over offtake, as imposed by future legislation, is feasible for N for cropping systems comparable to the system examined, but that the standard for P will probably turn out to be a tight one.

Effects of partial shading of the potato plant on photosynthesis of treated leaves, leaf area expansion and allocation of nitrogen and dry matter in component plant parts

Abstract Literature shows that the distribution of nitrogen (N) over leaf layers tends to follow the distribution of light. Nitrogen is regarded as moving away from poorly illuminated leaves. If operative in plant canopies, such mechanisms affect leaf longevity and the allocation of N and dry matter to plant parts. To examine such mechanisms in potato ( Solanum tuberosum L.) we conducted pot experiments with spaced plants in which the primary axis of the plant was subjected to shade treatments (50 or 90% shade), while the apical branches of the plant were illuminated as the control plants. N treatments were a limiting rate of N supply (N1) and a high rate of N supply (N2). Changes in leaf area, dry weight, N content (organic N and nitrate) and light saturated photosynthetic rate ( P max ) were recorded for particular leaf numbers. Leaf area, dry weights and total N content of all component plant parts were determined. Shaded leaves showed a lower specific leaf weight while leaf area was not affected. Fifty percent shade had little effect on age-related changes of leaf properties, but leaves senesced fast when subjected to 90% shade. Shading the primary axis enhanced apical branching, increased sizes of individual leaves and reduced stem:leaf weight ratio of non-shaded apical branches; partitioning of dry matter and nitrogen to tubers was less than in controls. It was concluded that these changes were not associated with enhanced remobilization of N from shaded plant parts; nor were they related to enhanced senescence of shaded leaves.

Genetic variation for resistance to low-temperature photoinhibition of photosynthesis in maize (Zea mays L.)

SummarySixty-seven inbred lines of maize were evaluated for resistance to low-temperature photoinhibition of photosynthesis, using a pulse-modulated chlorophyll fluorescence technique. The evaluation procedure was based on leaf discs, which were exposed to a high irradiance (1000 µmol/m2/s) at 7°C. The efficiency of open PSII reaction centres as a reflection of overall photosynthesis was measured before and after a photoinhibition-inducing treatment. Exposure of leaf discs to photoinhibitory condition for 2, 4, and 8 hours resulted in an efficiency reduction of 30, 53 and 83%, respectively. Testing of inbred lines showed large differences for photoinhibition susceptibility. The difference in photosynthetic efficiency between the most extreme lines after a treatment of eight hours was 39%. Resistance to photoinhibition was shown to be relevant under cool field conditions. It proved to be a trait strongly amenable to selection.

Heat-shock effects on photosynthesis and sink!!source dynamics in wheat ( Triticum aestivum L. )

To assess the mechanisms causing genotypic differences in heat tolerance of wheat (Triticum aestivum L.), physiological responses to a heat shock in a vegetative (‘end of tillering’) or a reproductive (‘early grain filling’) stage were studied. Three cultivars  Lavett, Ciano-79 and Attila  differing in adaptation to heat were grown in a glasshouse at a day/night temperature regime of 15/10 C and a 12-h daylength from sowing to ‘end of tillering’ and next at two day/night regimes of 25/20 and 18/13 oC under natural daylength. The heat-shock treatment consisted of an exposure of plants to temperatures raised gradually over a time-span of 12 hours to above 30 °C with a maximum of 38 °C during three hours at midday for three days either at the ‘end of tillering’ or at ‘grain filling’. A heat shock at the ‘end of tillering’ strongly reduced the rate of leaf photosynthesis. A similar heat shock during ‘grain filling’ decreased both rate of photosynthesis (source) and grain growth (sink). The rate of leaf photosynthesis was decreased by 40 to 70%, depending on cultivar and developmental stage. Photosynthesis fully recovered within 4 days after the heat-shock treatment was ended. The effects of the heat shock on biomass yield were more pronounced for treatments at ‘early grain filling’ than at ‘end of tillering’. However, the impact of a 3-day heat shock on biomass yield was less than the effects of the pre- and post-treatment growing temperature.

Development of leaf area and leaf number of micropropagated potato plants

Aboveground leaf area and leaf number development of in vitro produced potato plantlets was studied over three growth phases. In vitro plantlets were produced at 17 or 23°C (normalisation phase, 3 weeks), planted in soil at 18/12 or 26/20°C (transplant production phase, 2 weeks), and later transplanted at 18/12 or 26/20°C (tuber production phase, 6 weeks). Boosts in leaf area increase and leaf appearance occurred in the first days after planting to soil. A shock in leaf area increase occurred after the later transplanting. Both for plant averages and most individual plants, leaf area increase in all growth phases was best described by logistic curves, indicating growth limitations occurred in all phases. These limitations were least severe during the relatively short transplant production phase. Higher temperatures did not significantly increase leaf area during normalisation, increased leaf area during transplant production, and first increased but later reduced leaf area during tuber production. Higher temperatures increased leaf number in all phases. After-effects of normalisation temperature occurred during transplant production but no longer during tuber production. Aftereffects of transplant production temperature occurred during tuber production. After-effects were direct (affecting plants at the beginning of the next phase) or appeared later.