Harry F. Hodges

Crop simulation models in agronomic systems

Publisher Summary This chapter discusses some crop simulation models in agronomic systems. Many crop models or parts of crop models have been built to help the researcher and students understand the operation of some part of an agronomic cropping system, for example, soil water flow, stomata1 control, or fertilizer nutrient movement. In addition to understanding various parts of agronomic systems, the modelers want to see what can be expected to happen if some change is made in that system. Field tests are very expensive, especially as the numbers of variables and/or treatments increase, and years of results are needed. A proven model of the system helps to evaluate these treatments and indicates which ones could be expected to give the desired results. The cotton model, GOSSYM, has been widely validated. GOSSYM has been used in a user-friendly form on a PC microcomputer as a tool for on-farm management decisions pertaining to nitrogen fertilizer applications, irrigation scheduling, and timing of harvest-aid chemicals. By combining GOSSYM with an expert system program, COMAX, the on-farm management decisions have been run in several combinations to give the user an optimal plan for fertilizer and irrigation scheduling.

Interactions of CO2 enrichment and temperature on cotton growth and leaf characteristics

Abstract Studies on the interactive effects of atmospheric CO 2 and temperature on growth and leaf morphology, particularly on stomatal index and density are limited. Upland cotton was grown in naturally-lit plant growth chambers at 30/22°C day/night temperatures from planting until squaring or the fifth or sixth leaf emerged. Five growth chambers were maintained at ambient (350 μ l l −1 ) CO 2 and another five at twice ambient (700 μ l l −1 ) CO 2 throughout the experiment. Day/night temperature treatments of 20/12, 25/17, 30/22, 35/27 and 40/32°C were imposed at each CO 2 treatment for 42 days after squaring. The plants were irrigated with half-strength Hoaglands nutrient solution three times per day. Growth of plant parts was determined at the end of the experiment. Stomatal characteristics, nonstructural carbohydrates and specific leaf weight were measured on the fully expanded tenth mainstem leaf. Stomatal density and index were not affected by elevated CO 2 . Stomata and epidermal cell numbers per leaf increased in high CO 2 and were positively correlated with final leaf sizes irrespective of CO 2 level. Our results suggest that plants do not acclimate to elevated CO 2 by changing stomatal density within a single generation. Leaves had greater area and accumulated more biomass when grown in high CO 2 . Growth stimulation expressed as dry weight at 700 μ l l −1 over dry weight at 350 μ l l −1 CO 2 was uniform across temperatures. Temperature optimum for vegetative and reproductive growth was 30/22°C and was not altered by CO 2 enrichment. Fruit retention was severely curtailed at the two higher temperatures compared to 30/22°C in both CO 2 environments. Increased carbohydrate storage in leaves may be an added advantage for initiation and growth of vegetative structures such as branches at all temperatures. However, it is unlikely that high temperature effects on flower abortion will be ameliorated by high CO 2 . Species/cultivars that retain fruits at high temperatures would be more productive both in the present-day cotton producing environments and are even more desirable in the future warmer world.

Carbon dioxide enrichment and temperature effects on cotton canopy photosynthesis, transpiration, and water-use efficiency☆

Abstract The objectives of this study were to evaluate effects of ambient and double ambient [CO2] at a range of growing temperatures on photosynthesis, respiration, transpiration, water-use efficiency and dry matter accumulation of cotton plants (Gossypium hirsutum L., cv. DPL 50). In Experiment I, plants were grown outdoors until first bloom, then transferred into naturally lit growth chambers and grown for 22 days at 30/18°C with five CO2 concentrations varying from 350 to 900 μl l−1. In Experiment II, air temperatures were maintained at 20/12, 25/17, 30/22, and 35/27°C day/night during a 70-day experimental period with [CO2] of 350 and 700 μl l−1 at each temperature. Photosynthesis increased with [CO2] from 350 to 700 μl l−1 and with temperature. Plants grown at 35/27°C produced fewer bolls due to abscission compared with plants grown at optimum temperatures (30/20°C). At higher [CO2], water-use efficiency increased at all temperatures due mainly to increased canopy photosynthesis but also to more limited extent to reduced canopy transpiration. Increased photosynthesis at higher [CO2] resulted in greater dry matter accumulation at all temperatures except at 20/12°C. Respiration increased as dry matter and temperature increased. Plants grown at higher [CO2] had less respiration per unit dry matter but more per unit area. These results indicate that future increases in [CO2] are likely to benefit cotton production by increasing carbon assimilation under temperatures favorable for cotton growth. Reduced fruit weights at higher temperatures indicate potential negative effects on production if air temperatures increase as projected in a high-CO2 world.

Nitrogen nutrition and photosynthesis in leaves of Pima cotton 1

Abstract The influence of nitrogen (N) on dry matter accumulation and yield in cotton is well documented, but its effects on carbon (C) assimilation and transpiration are less clear. The objectives of this study were to characterize leaf photosynthetic and stomatal responses of Pima cotton (Gossypium barbadense L., cv. S‐6) plants, grown under different N nutritional regimes. Pima cotton was grown in pots under natural environmental conditions. Varying N regimes were imposed on 20‐day‐old plants by fertilizing with nutrient solutions containing 0, 0.5, 1.5, and 6 mM of nitrate (NO3) concentrations. Net carbon dioxide (CO2) assimilation rates, stomatal conductance, internal CO2 partial pressures, transpiration rates, leaf carbohydrate status, ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco) activities, and leaf N concentrations were determined in the youngest fully expanded leaves. Net photosynthetic rates, stomatal conductance and transpiration were positively correlated with leaf N concentration...

Carbon dioxide and temperature effects on pima cotton growth

Abstract Temperature and CO2 are major environmental variables that affect plant growth and development. Limited information is available concerning how these factors affect plants, as well as specific interactions between the two. We conducted two experiments in controlled environmental chambers where temperature and CO2 were controlled and other environmental factors were not limiting. The purpose was to determine how cotton grew and responded to a range of temperatures and CO2 concentrations. During vegetative development, stem growth was quite sensitive to CO2 resulting in more effective early-season light capture. Plants did not develop more nodes when exposed to additional CO2, while node number increased more at higher temperatures. Individual leaf growth was about 18% greater at optimum temperature in 450 μl l−1 than in 350 μl l−1 CO2, but did not increase from 450 μl l−1 CO2 to 700 μl l−1 CO2. However, the time required for a leaf to reach mature size was not influenced by CO2. Leaf area, on the whole plant basis, was about 33% greater on plants grown at optimum temperature in high CO2 than in ambient CO2. The greater leaf area on a whole plant basis was achieved by a combination of larger leaves and additional leaves produced primarily on the branches. There was a 28% increase in number of bolls produced at 700 μl l−1 CO2 at optimum temperature compared with bolls produced at 350 μl l−1 CO2. There was not, however, an increase in boll size due to high CO2. At 35.5°C, little growth response to high CO2 environments occurred at 700 μl l−1 CO2 compared with 350 μl l−1 CO2, but approximately a 45% increase occurred in the plants grown at 18.9–26.9°C. Less total biomass was produced at 35.5°C than at 26.9°C and no bolls were produced in either CO2 environment at the higher temperature. The most important response to temperature and CO2 occurred at high temperatures where the effects of elevated CO2 on plant growth were masked by apparent high-temperature injury that limited growth of all plant organs, particularly, reproductive growth.

Photon flux density versus leaf senescence in determining photosynthetic efficiency and capacity of Gossypium Hirsutum L. Leaves

Abstract Within any agronomic crop, multiple processes contribute to the loss of carbon uptake with increasing leaf age. Leaves within the crop canopy experience increasingly lower insolation levels with increasing age due to development of leaves at higher canopy positions. This overshadowing occurs concurrently with declining photosynthetic activity due to physiological alterations with leaf aging. Research exploring the photosynthetic response to these changing light conditions and leaf senescence has failed to adequately separate environmental from physiological responses. Additionally, growth chamber grown plants often show very different photosynthetic responses to photon flux during the aging process than leaves grown under the highly variable photon flux levels in the natural environment. In this study, cotton ( Gossypium hirsutum , L.) leaves were held at various levels of full sun in an outside growing area and photosynthetic characteristics were determined with increasing leaf age. Photosynthetic efficiency and capacity decreased rapidly and substantially as the leaves aged; the decline in maximal photosynthetic capacity was more substantial than that of the photosynthetic efficiency. However, no statistically significant differences in leaf photosynthetic characteristics were observed due to the photon flux environment experienced during the aging process. The changes in leaf photosynthetic responses to light environment during leaf aging were solely the result of physiological changes within the senescing leaf and not the result of differences in PFD environment. Similar sun-to-shade adaptations in leaf protein and chlorophyll levels reported in previous studies were observed in response to photon flux environment, indicating an adjustment of the photosynthetic apparatus to incident light. These results have particular significance for leaves within crop canopies that often develop under near-full sun conditions, and gradually experience deeper levels of shade throughout the leaf life span as upper canopy foliage develops.

Automated System for Measurement of Evapotranspiration from Closed Environmental Growth Chambers

ABSTRACT Asystem for the automatic measurement of evapotranspiration is described. The system was designed for use with closed environmental growth chambers in which crops are grown. Although measurements were taken every 15 min, longer measurement periods can be used. The system was very reliable and accurate over crop growing periods up to five months.

Physiological Simulation of Cotton Growth and Yield

Scientists early in the twentieth century sought ways to describe and predict plant growth. Gregory (1917) and Blackman (1919) developed methodology called “growth analysis” to describe net assimilation rate, and compared dry matter accumulation to compound interest. By the middle of the century, leaf area index and light interception were recognized as important parameters for estimating photosynthesis in crop stands and were thus related to canopy dry matter growth. During the 1960s and 1970s, leaf and canopy photosynthesis were described using commercially available gx analyzers, radiation sensors, and other devices for measuring environmental conditions that facilitated studies remarkably. There were extensive debates regarding leaf angles, radiation attenuation, carbon accumulation, and maintenance and growth respiration. Several laboratories became interested in relating information on environmental conditions to photosynthesis, plant growth, and harvestable yield. The development of simulation models of the various processes had become feasible. The objectives and validation methods varied widely among crop modelers.

Exploring the Limitations for Cotton Growth and Yield

Abstract Most crops do not achieve their genetic potential, even under the best crop husbandry, because of environmental constraints. Improvements in crop adaptation to environmental stresses can be better assessed if the maximum potential is known. Here, we report the results from cotton plants grown in naturally lit growth chambers in which temperature and atmospheric carbon dioxide concentration [CO2] were controlled and varied systematically under optimum water and nutrient conditions. Photosynthesis of cotton canopies was measured continuously along with other related vegetative growth parameters and abiotic variables. Cotton canopies growing under potential growth conditions intercept most of the radiation available in the US Midsouth after beginning flowering and are not light-saturated. Present-day cotton cropping practices schedule the maximum crop demand for photosynthates to occur during declining solar radiation. Growing plants in high CO2 results in augmented vegetative growth during fruiting that enhances photosynthesis. Rising atmospheric CO2 concentrations should also benefit growth and yield. Temperature has only a small effect on canopy photosynthesis. Temperature, however, strongly influences vegetative growth and development, light capture during the vegetative period, and light conversion efficiency during much of the boll-filling period. Temperatures above 28°C limit both vegetative growth and more importantly boll retention or sink capacity. To achieve maximum production, it will be necessary to increase fruit production efficiency and light conversion efficiency. The former is more important than the latter in high-temperature environments. Cotton crops are capable of much higher productivity than typically observed even under the best management conditions.