Nutrient Uptake Model Research Articles

Root, shoot and soil parameters required for process-oriented models of crop growth limited by water or nutrients

A review is given of the prospects for using process-oriented models of water and nutrient uptake in improving ‘integrated agriculture’. Government-imposed restrictions on the use of external inputs will increase the likelihood of (temporary) nutrient or water stress in crop production in NW Europe and thus a better understanding is required of shoot-root-soil interactions than presently available. In modelling nutrient and water uptake, three approaches are possible: 1) models-without-roots, based on empirically derived efficiency ratios for uptake of available resources, 2) models evaluating the uptake potential of root systems as actually found in the field and 3) models which also aim at a prediction of root development as influenced by interactions with environmental factors. For the second type of models the major underlying processes are known and research can concentrate on model refinement on the one hand and practical application on the other. The main parameters required for such models are discussed and examples are given of practical applications. For the third type of models quantification of processes known only qualitatively is urgently needed.

Approaches to modelling the uptake of water and nutrients in agroforestry systems

This review presents information about root systems of crops and trees and describes approaches that have been used to model uptake of water and nutrients in crops that may have application to agroforestry systems. Only a few measurements of the distribution of tree roots in agroforestry systems have been published and these are predominantly in alley cropping systems with young trees. Therefore, a major limitation to developing water and nutrient uptake models for trees is the lack of adequate measurements and conceptual models for describing the distribution of roots spatially and temporally. Most process-based modelling approaches to water and nutrient uptake integrate the activities of a single root over the whole root system. Several difficulties can be foreseen with applying these approaches to roots of older trees including the presence of mycorrhizal associations so that the root surface is not the site of uptake, the uncertainty as to whether all tree roots are active in taking up water and nutrients, and the fact that, unlike annual crops, trees have substantial reserves of nutrients that can be mobilised to support growth so that the notion of a plant demand regulating uptake may prove difficult to define. The review concludes that a programme of experimental measurements is required together with modelling using approaches both in which roots are implicit, and in which process-based models with roots allow competitive ability to be assessed.

Multi-dimensional sensitivity analysis and ecological implications of a nutrient uptake model

Mechanistic models of nutrient uptake are essential to the study of plant-soil interactions. In these models, uptake rates depend on the supply of the nutrient through the soil and the uptake capacity of the roots. The behaviour of the models is complex, although only six to ten parameters are used. Our goal was to demonstrate a comprehensive and efficient method of exploring a steady-state uptake model with variation in parameters across a range of values described in the literature. We employed two analytical techniques: the first a statistical analysis of variance, and the second a graphical representation of the simulated response surface. The quantitative statistical technique allows objective comparison of parameter and interaction sensitivity. The graphical technique uses a judicious arrangement of figures to present the shape of the response surface in five dimensions. We found that the most important parameters controlling uptake per unit length of root are the average dissolved nutrient concentration and the maximal rate of nutrient uptake. Root radius is influential if rates are expressed per unit root length; on a surface area basis, this parameter is less important. The next most important parameter is the effective diffusion coefficient, especially in the uptake of phosphorus. The interactions of parameters were extremely important and included three and four dimensional effects. For example, limitation by maximal nutrient influx rate is approached more rapidly with increasing nutrient solution concentration when the effective diffusion coefficient is high. We also note the ecological implications of the response surface. For example, in nutrient-limited conditions, the rate of uptake is best augmented by extending root length; when nutrients are plentiful increasing uptake kinetics will have greater effect.

Evaluation in field conditions of a three-dimensional architectural model of the maize root system: Comparison of simulated and observed horizontal root maps

Most existing water and nutrient uptake models are based on the assumption that roots are evenly distributed in the soil volume. This assumption is not realistic for field conditions, and significantly alters water or nutrient uptake calculations. Therefore, development of models of root system growth that account for the spatial distribution of roots is necessary.

Modeling individual nutrient uptake by plants: Relating demand to microclimate

This paper proposes an approach for modeling plant uptake of individual nutrients based on incident microclimatic variables and independent of water uptake. Current nutrient uptake models, though quite complex, have not been developed in a form directly applicable to nutrient management systems for greenhouse crop production. This paper proposes an approach for predicting plant nutrient use based on the assumption that plant nutrient demand, as determined by photosynthetic rate, determines the required rate of nutrient uptake for optimal growth. This general model allows specific models to be developed with direct functional relationships between individual nutrient uptake rates and incident microclimatic variables. A simple model is presented which applies nutrient demand directly to photosynthetic photon flux density.

Computer-based System for Dynamic Control of Greenhouse Tomato Grown in NFT System

To achieve high yield and better quality of soilless greenhouse tomato, it is necessary to keep the nutrient concentrations in the root environment at the target levels. Dynamic control of the nutrient solution composition can be used for this purpose. We developed a computer program that dynamically adjusts nutrient solution compositions based on various climatic and agronomic characteristics. The program integrates nutrient uptake and crop transpiration models and is part of a general-purpose greenhouse management and control software system developed at Laval University (GX). The architecture of the system and some simulation results comparing the effect of various control scenarios on the evolution of the composition of nutrient solutions are presented.

Computer-based System for Dynamic Control of Greenhouse Tomato Grown in NFT System

To achieve high yield and better quality of soilless greenhouse tomato, it is necessary to keep the nutrient concentrations in the root environment at the target levels. Dynamic control of the nutrient solution composition can be used for this purpose. We developed a computer program that dynamically adjusts nutrient solution compositions based on various climatic and agronomic characteristics. The program integrates nutrient uptake and crop transpiration models and is part of a general-purpose greenhouse management and control software system developed at Laval University (GX). The architecture of the system and some simulation results comparing the effect of various control scenarios on the evolution of the composition of nutrient solutions are presented.

Temporal variability and scaling behaviour in the fine‐root system of kiwifruit (Actinidia deliciosa)

ABSTRACTWe show that temporal variability in root populations can depend upon the scale of measurement (particularly the sampled soil volume). The presence of roots in a range of volumes of soil was studied using perspex tubes installed horizontally into the soil around three mature kiwifruit vines. Roots intercepting lines scored on the tubes were counted using a periscope. For small volumes of soil (c. 2–4 cm3) the root counts varied with time in a very irregular manner, and as the interval between measurements increased the autocorrelation between the measurements decayed rapidly. At about half of the locations monitored there was no significant autocorrelation between measurements 27 d apart. Linear interpolation in these time series was unreliable, and where the correlation dimension could be resolved it was usually non‐integer (suggesting chaotic behaviour). The time series measured at different locations were poorly correlated, indicating weak coordination. As the observed soil volume increased, the coordination between locations improved, the autocorrelation function increased, and linear interpolation errors decreased (although these remained substantial). Clearly there are considerable fundamental constraints on our ability to predict the root behaviour of kiwifruit vines at scales that are appropriate for mechanistic models of nutrient and water uptake. We discuss the need for a new conceptual model of the fine‐root systems of kiwifruit and similar species.

Allocation of mass in trees subject to nitrogen and magnesium limitation.

It has previously been shown that lack of magnesium, potassium or manganese depresses allocation of new mass to roots in trees, and that these elements often occur in low amounts in declining forest stands. A model for tree growth and nutrient uptake was used to examine the effect of allocation pattern of new plant mass on growth and development in soils with low nutrient concentrations. Growth parameters and empirical allocation functions from steady-state experiments with birch (Betula pendula Roth.) and Norway spruce (Picea abies (L.) Karst.) limited by N or Mg were used in the simulations. The simulation results show that plant nutrient concentration is sensitive to decreases in soil Mg concentration and is not counteracted by an increased allocation of plant mass to roots. A 50% reduction in the optimal soil Mg concentration decreased the plant Mg concentration to the threshold of survival, whereas a 50% reduction of soil N had much less effect. Birch was more sensitive to low soil Mg concentration than Norway spruce. We conclude that, in the discussion of forest decline, it may be important to consider the decreased allocation of mass to roots when Mg (or K or Mn) is in short supply.

Fall in nutrient demand per unit root length during the linear phase of plant growth

If root length increases in proportion to plant weight, growth is expolinear, and plant composition is constant, then there is fundamental drop in nutrient demand per unit root length during the linear growth phase. This is in contrast to the exponential phase, when increments of growth and hence of nutrient demand are proportional to plant size and thus to root length: in the linear growth phase, they are constant despite increasing root length. For nutrient uptake models in which demand is based on growth and uptake is based on root length, this would suggest a tendency for nutrients to accumulate in the plant as it grows.

Prediction of phosphorus uptake by a mechanistic model in a low phosphorus highly weathered soil as affected by mycorrhizae inoculation

Abstract Mechanistic models need to be validated before being widely used. The Barber‐Cushman mechanistic nutrient uptake model has successfully predicted phosphorus (P) uptake in high‐P soils, but it has not been tested in soils with low available P. Some assumptions of this model (no influence of mycor‐rhizae and root hairs on nutrient uptake) may have different implications according to the soil P level. The objective of this study was to test the ability of the Barber‐Cushman model to predict P uptake for corn in an Oxisol with low P values as influenced by mycorrhizae inoculation. The experiment was carried out in a greenhouse, in a factorial with two levels of P (25 and 100 mg/kg), of limestone (pH 4.7 and 5.5), and of mycorrhizae inoculation (with and without). Observed P uptake was determined in the roots and in the shoots of 46‐day‐old corn plants. The predicted P uptake by the model was calculated using a computer program. There was a good agreement between observed and predicted P uptake (r2 = ...

Analyzing Root Competition with Dirichlet Tessellation for Wheat on Three Landscape Positions

AbstractThe underlying mechanisms for root competition are not completely understood; yet, it is important to accurately define the zone of influence around individual roots for nutrient or water uptake, particularly when modeling nutrient uptake processes. The objectives of this study were to investigate the use of the Dirichlet tessellation for quantifying soil polygons around roots of spring wheat (Triticum aestivum L. cv. Katepwa) grown on three landscape positions and to quantify the root spatial patterns. Roots were exposed on a horizontal soil plane at 2‐, 5‐, and 10‐cm depths and mapped on acetate sheets at 21, 45, and 88 days after planting (DAP) for shoulder, backslope, and footslope positions. Tessellation of scanned root maps showed that soil polygons decreased in size during the sampling period; however, polygon areas increased with soil depth regardless of slope position and ranged from 0.08 to 52.77 cm2. Eccentricity averaged 0.74 ± 0.01, indicating that polygons were more circular than elliptical and root displacement averaged one‐third the distance from the polygon center to the polygon edge. Root spatial patterns using R‐index values, showed that roots on shoulder positions had clumped to random patterns while roots at the footslope had random to regular patterns. Root spatial patterns and displacement for wheat violated the assumptions used in nutrient uptake modeling and should be incorporated into future modeling efforts. Dirichlet tessellation is an effective procedure for analyzing root competition and has promise for multispecies competition if different root systems can be weighted by morphological or physiological characteristics.

Use of Theissen Areas in Models of Nutrient Uptake in Forested Ecosystems

AbstractNutrient uptake models have generally incorporated simplifying assumptions, one of which is that roots are regularly arrayed in space. This allowed an evaluation of an average root to be extrapolated to a whole plant by simply multiplying the single root result by the total root length. In low‐fertility soils, particularly those with very low buffer powers, this regular root assumption causes nutrient uptake to be overestimated. Nutrient uptake models would be more realistic if Theissen areas were used as the area of influence of roots. A computer program for computing Theissen maps for a hydrological application has been adapted, tested, and applied to nutrient uptake by roots in a forested ecosystem. Nutrient uptake using Theissen areas is compared with uptake based on the assumption of regularly arrayed roots and with worst‐case situations of uptake influenced by nearest‐neighbor roots. For slash pine (Pinus elliottii Engelm. var. elliottii) growing on a Spodosol of the lower Coastal Plain of the USA, root patterns of the A horizon have been found to be random, not regular. Computer simulations of nutrient uptake showed that the average root procedure was appropriate for K under the conditions investigated, but suggested that P uptake would be overestimated unless the spatial pattern of roots was included. Ratios of Theissen radii to 1/2 nearest neighbor distances show that root areas of influence tend to be noncircular or that roots are eccentrically positioned, either of which are violations of assumptions used in nutrient uptake models.

Aerial accumulation and partitioning of nutrients by hard red spring wheat

Abstract Periods of maximum hard red spring (HRS) wheat (Jriticum aestivum L.) nutrient demand need to be determined in order to develop best nutrient management practices, and to provide data for nutrient uptake modeling. Aerial (aboveground biomass) whole plant samples of irrigated HRS wheat were collected from the field at 16 growth stages and separated into leaves, stems, heads, and grain for dry matter determinations and analyzed for N, P, K, Ca, Mg, S, Cl, Zn, Mn, Fe, and Cu concentrations. Accumulation curves were computed for each plant part for the growing season from compound cubic polynomial models based on accumulated growing degree units (GDUs). Total aerial accumulations of dry matter, N, P, K, Ca, Mg, S, Cl, Zn, Mn, Fe, and Cu were 14400, 116, 30.8, 103, 9.2, 9.3, 15.2, 32.3, 0.18, 0.58, 2.05, and 0.045 kg/ha, respectively. Grain at maturity accumulated greater than 78% of the total aerial N, P, and Zn, while it contained less than 20% of the aerial accumulated K, Ca, Cl, and Fe. Nitrogen a...

Weed effects on early K and P nutrition and growth of slash pine on a Spodosol

Slash pine ( Pinus elliottii Engelm. var. elliottii) seedlings were grown on s Spodosol and without total weed control. During the 187 days after planting, shoots and roots of both trees and weeds were sampled four times to determine (1) the effects of weeds on early K and P nutrition and growth of slash pine, (2) the correlation between either above-ground weed biomass or live coverage and the root-length density of weeds, and (3) provide a data set to test a nutrient uptake model. During the initial 187 days, trees in the weed treatment lost half their initial K content, yet biomass and P content remained unchanged. Concentrations of K in needles from this treatment concurrently decreased from 7.7 to 2.5 mg K g −1. Even trees in the weed-free treatment lost K for the first 116 days before taking up significant amounts of K and P and increasing four-fold in biomass by Day 187. Tree root growth rates were also reduced in the presence of weeds. Grass root-length density was poorly correlated with above-ground biomass or live coverage ( r 2 values 0.37 and 0.47, respectively). Hence, above-ground attributes of weeds were considered poor surrogates for root-length density.

Mechanistic simulation models of nutrient uptake: A review

Mechanistic models of nutrient uptake consider diffusion and mass flow acting simultaneously to supply nutrients to the sorbing root surface. Plant parameters that determine nutrient uptake include those describing changes in root geometry and size due to root growth and others describing kinetics of the nutrient uptake process. Mechanistic models generally assume that nutrient uptake occurs evenly along the roots that are uniformly distributed in homogeneous and isotropic soil having no temporal and spatial gradients in volumetric moisture content. Uptake of immobile nutrients (like P and K) is mainly determined by the soil-supply parameters and is well predicted by the simulation models. In contrast, uptake of mobile nutrients (e.g. Ca and Mg) that usually accumulate at the root surface is determined mainly by the plant-uptake parameters; prediction of uptake of those nutrients is subject to a much wider error due to uncertainties of applying kinetic parameters measured on hydroponically-grown plants to soil-grown plants. Comparison of model-predicted and experimentally-observed uptake values should be done by calculating the mean squares of deviates instead of performing regression analysis, especially if data that encompass a relatively wide range in root length are considered. Complementary-ion effects occurring at the soil-root interface raise the need for developing a multi-nutrient uptake model that will simultaneously calculate uptake of several essential nutrients taking into account interactions among them.

Soil phosphorus levels needed for equal P uptake from four soils with different water contents at the same water potential

Soil volumetric water contents, φ, at −33 kPa potential may vary with soil from 0.06 to 0.70. Because P diffusion depends on φ, most economic P fertilizer rates required for different soils may require adjusting according to their soil-water relationships. The objective of this study was, after experimentally verifying a mechanistic nutrient uptake model on a series of soils varying in θ at −33 kPa potential, to use the model to predict labile P levels needed for each of these soils to achieve equal P uptake by maize (Zae mays L.) and verify these predictions. Maize was grown in a pot experiment using four soils having θ of 0.13, 0.20, 0.26, and 0.40 at −33 kPa each at 0, 200, and 400 mg kg-1 of added P. When root parameters obtained experimentally were used, predicted P uptake with the uptake model agreed with observed P uptake, y=0.99x+9.08 (r2=0.98). When P uptake was plotted vs. soil solution P, Cli, the relation varied with soil. The higher the θ the lower the Cli needed for equal P uptake. A similar relation was found between P uptake and diffusible soil P, Csi. Differences between the two plots occurred because of differences among soils in buffer power, ΔCsi/ΔCli. The Csi vs. P added relation was used to calculate differences among soils in the Csi needed to obtain equal P uptake. The Csi values ranged from 1.3 to 4.0 mmol kg−1. The calculated values were used in a second pot experiments to verify the predictions. No significant difference (α=0.05) in P uptake occurred. The results of this research indicate that the mechanistic nutrient uptake model can be used to predict the degree of adjustments in Csi needed to obtain the most economic P fertilizer rates among soils varying in θ.

Use of a mechanistic uptake model for evaluating phosphate fertilizer materials

Abstract A mechanistic nutrient uptake model that predicts nutrient uptake using values for root growth and morphology, uptake kinetics and nutrient supply to the root by mass flow and diffusion has given close agreement between predicted uptake and observed uptake. The model can be used to evaluate availability of fertilizer materials added to the soil without plant growth experiments. The model also indicates the reason for differences between fertilizers. A study was made to evaluate the P uptake from monocalcium phosphate (MCP), diammonium phosphate (DAP), applied to 13 soils. In a second experiment P uptake from MCP, DAP, rock phosphate and partially acidulated rock phosphate were compared at soil pH's of 5.0 and 5.7. Increasing soil pH reduced P availability from rock phosphate and partially acidulated rock phosphate and MCP but not from DAP. The results indicate the usefulness of the model for evaluating fertilizers.

Root-soil contact of maize, as measured by a thin-section technique

In models of oxygen, water and nutrient uptake by plant roots, the degree of root-soil contact is an important parameter. An observation technique is required to evaluate to what extent root-soil contact depends on plant species, soil texture and structure. Thin sections for studying soil structure may be used for this purpose, provided that roots do not shrink during section preparation, and that all root cross sections are recognized. Maize was grown in pots with soil aggregates obtained by sieving and compacting to three bulk densities. Thin sections were made by freeze-drying samples before impregnating the soil with resin. Two checks were made on the validity of the method. Firstly, visual appearance of roots with intact epidermis, cortex and other tissues did not show signs of shrinkage. Secondly, the agreement was checked between root lengths obtained by washing duplicate soil samples and the number of root cross sections counted on horizonal and vertical thin sections. For the latter, the angle at which roots intersected the thin-section plane was determined from the shape of the cross sections. The frequency distribution of calculated angles was in agreement with the frequency distribution expected for a randomly oriented set of cylinders when an error term was included in the simulated measurements. Some results are presented for a field test of the thin-section method with barley on a calcareous marine sandy loam. Root hairs, apparently undamaged by sample preparation, are important for bridging the gap between roots and soil in this situation. According to the experience presented, the thin-section technique is suitable to derive the degree of root-soil contact, as influenced by species, soil texture and structure, in samples obtained from pot or field experiments.

Modeling magnesium, phosphorus and potassium uptake by loblolly pine seedlings using a Barber-Cushman approach

The Barber-Cushman mechanistic nutrient uptake model, which has been utilized extensively to describe and predict nutrient uptake by crop plants, was evaluated for its ability to predict K, Mg, and P uptake by loblolly pine (Pinus taeda L.) seedlings. Sensitivity analyses were also used to investigate the impact of changes in soil nutrient supply, root morphological, and root uptake kinetics parameters on simulated nutrient uptake. Established experimental techniques were utilized to define the 11 parameters needed to model uptake by 1-0 seedlings of K, Mg, and P from a modified A horizon soil (Lilly series). Model predictions of K and P uptake over a 180-d growth period were underestimated by 6 and 11%, respectively. Estimates of Mg uptake were underestimated by 62%. While the level of agreement between predicted and observed K and P values was quite acceptable, analysis of parameter values and results of sensitivity analyses both indicated that the model underestimation of Mg uptake was the result of applying an Imax value developed under relatively low Mg concentration to a situation in which the functional Imax would be much higher due to the dominance of passive versus active uptake. Overall results of sensitivity analyses indicate that under the circumstances investigated, Imax, was the primary variable controlling plant uptake of K, Mg, and P. The dominance of this term over others was due to the relatively high Cli values for all three nutrients. Reducing (-50%) or increasing (+ 100%) other soil supply, root morphological, and remaining root uptake kinetics values did not substantially alter model estimates of nutrient uptake.