Thomas J. Gerik

Radiation-use efficiency response to vapor pressure deficit for maize and sorghum

Variability within a crop species in the amount of dry mass produced per unit intercepted solar radiation, or radiation-use efficiency (RUE), is important for the quantification of plant productivity. RUE has been used to integrate (1) leaf area, (2) solar radiation interception, and (3) productivity per unit leaf area into crop productivity. Responsiveness of RUE to vapor pressure deficit (VPD) should relate closely to responsiveness of CO2 exchange rate (CER) to VPD. The objective of this study was to compare independent RUE measurements to published response functions relating VPD with RUE of maize (Zea mays L.) and grain sorghum [Sorghum bicolor L. (Moench)]. Data sets from five locations covering a wide range of mean VPD values were compared to published response functions. Predicted RUE values were nearly always within the 95% confidence intervals of measurements. Measured RUE of maize decreased as VPD increased from 0.9 to 1.7 kPa. For sorghum, measured values of RUE agreed closely with predictions. RUE of sorghum decreased as VPD increased from 1.1 to 2.2 kPa. The relative RUE:VPD responses for these two species were similar to CER:VPD responses reported in the literature. Thus, these RUE:VPD responses may be general and appear to be related to carbon exchange rates. We calculated the expected impacts of VPD on RUE at three USA locations during maize and sorghum growing seasons. The RUE:VPD equations offer hope in describing location effects and time-of-year effects on RUE.

Cotton Leaf Photosynthesis and Carbon Metabolism

Photosynthesis is the basis of plant dry matter production and a major determination of yield in cotton (Gossypium hirsutum L.). Much of the cotton yield increases in recent years can be attributed to the improved partitioning of dry matter into reproductive growth rather than vegetative growth. However, this strategy can only be taken so far before the amount of photosynthesizing leaf area becomes the limiting factor. Therefore, improved plant photosynthesis coupled with good dry matter partitioning could lead to additional yield improvements. Research has identified both genetic and environmental variations in the rate of cotton photosynthesis. Superior leaf photosynthetic performance has been exhibited by okra and super‐okra leaf types compared to the normal leaf types. Photosynthetic variation has also been identified within the normal leaf type pool of germplasm. However, geneticists have generally not targeted this trait for genetic improvement in cotton. In addition, leaf tissue concentration of the three major plant nutrients (nitrogen, potassium, and phosphorus) need to be maintained at sufficient levels for optimum photosynthesis. Under deficient soil fertility conditions, supplemental fertilization can increase overall growth due to both increased leaf area production and increased photosynthetic rate per unit leaf area. Both excessive and deficient soil moisture conditions can depress the photosynthetic performance of the plant and its corresponding growth. Similarly, an optimum temperature range exists, above and below which the photosynthesis is negatively impacted. This knowledge of variation in both genetic and environmental influences on photosynthesis offers hope of improved photosynthetic performance through either a concerted genetic selection or modified production systems that minimize exposure to some of the rate‐limiting environmental conditions.

Foliar-applied methanol effects on cotton (Gossypium hirsutum L.) gas exchange and growth☆

Abstract Reports that foliar-applied methanol greatly enhanced growth of C 3 crops has stimulated considerable interest. Experiments were conducted to evaluate foliar application of methanol on cotton ( Gossypium hirsutum L.) growth, leaf gas exchange and water use. Aqueous solutions of 0 (control), 10, 20 and 30% (v/v) methanol were applied to well-fertilized and watered plants of cultivar G&P 74 + grown under field and greenhouse conditions. Foliar-applied methanol increased CO 2 assimilation ( A ) and leaf conductance to CO 2 ( g ) in both field and greenhouse experiments up to 3 weeks after application, but did not consistently change intercellular CO 2 concentration ( c i ) or leaf water-use efficiency (LWUE, μmol CO 2 /mol H 2 O). Increasing the concentration of aqueous methanol above 10% solution did not further increase A or g in both field and greenhouse experiments. Dry matter accumulation, leaf area, fruit number, main stem node number and plant water use did not differ between the control and methanol-treated plants. Although these results indicate that methanol increases leaf gas exchange of cotton, they fail to validate previous reports of large increases in cotton growth and transpiration efficiency.

Planter Depth-Control: I. Predictions and Projected Effects on Crop Emergence

ABSTRACT PLANTER depth control with four wheel designs was evaluated on the basis of the predicted effects on simulated emergence for four crops. A linked front and rear depth control wheel design performed similar to rear and front depth control wheels. Side wheels produced the best performance, but they are too wide for solid-seeded planting narrow rows in crop residues. Depth control wheel position varied the simulated emergence as much as 36%. The simulation models proved useful in evaluating depth control mechanisms and could be extended to field situations by using specific surface topography and seed emergence data for response prediction.

Planter Depth Control: II. Empirical Testing and Plant Responses

ABSTRACT PLANTING depth control innovations are needed to improve the reliability of performance of no-tillage planters and drills. Four depth control designs were empirically evaluated with grain sorghum and corn crops in two different field conditions. An experimental no-tillage planter opener was used with each depth control. The field surface undulations were characterized prior to planting. Wheat stubble had higher frequency undulations than sorghum stubble. Stubble type affected mean planting depth and caused a shift in frequency distributions of planting depths for front and linked wheels. Dual rear presswheels malfunctioned by sinking into loosened soil and produced deeper and the most variable planting depths. Dual front depth control wheels gave significantly more variable planting depths than the side wheels and linked wheels at the highest applied downpressure. The best choice for depth control remains undecided between traditional wide dual side wheels and narrow experimental linked front-rear wheels. These results generally agree with simulation results from Part I of this series of papers

Photoperiod and temperature effects on tropically- and temperately-adapted sorghum

Abstract Grain yields of tropically-adapted (TA) sorghum hybrids far exceed those obtained with temperately-adapted (TE) sorghums in south Texas and other more tropical areas. This study was conducted to determine if photoperiod, temperature, and/or photoperiod-temperature interactions were responsible for the observed differences between TA and TE sorghum hybrids. Plants were grown in temperature-controlled glasshouses at two temperatures, 30/20 and 35/25 (day/night, °C). Three planting dates were used to attain different photoperiod regimes. Generally, the TA hybrid ATx623 × RTx430 maintained more green leaves, as compared to the TE hybrid ATx × RTx415. Both TA and TE hybrids senesced the same number of leaves regardless of temperature. Differences in leaf area at physiological maturity between TA and TE hybrids were more related to leaf number/plant and leaf-blade area than the number of leaves senesced. Phenology and leaf area development varied with planting date, temperature, and hybrid. The duration of vegetative development (GS1) was greater for TA hybrids when grown under short daylengths and low temperature. At high temperatures, GS1 was similar for TA and TE hybrids under the short daylengths of planting date 3, but differed among hybrids when grown under the longer daylengths of planting dates 1 and 2. Also, under short daylengths the hybrids derived from TA parents produced more leaves and greater leaf area only at the high temperature. Under the long daylength (planting date 2), TA hybrids produced more leaves and greater leaf area than the TE hybrid, irrespective of temperature. These findings suggest that sorghums converted for U.S. adaptation still exhibit some degree of photoperiodic sensitivity regarding phenological development and plant growth, but the TA hybrids have the ability to alter their phenological development and plant growth to maximize their leaf area under a wider range of environmental conditions.

Evaluation of new farming technologies in Ethiopia using the Integrated Decision Support System (IDSS)

Highlights • We propose a modeling framework that assesses environmental and economical consequences of agricultural intensification.• Agricultural interventions were evaluated using IDSS in two study sites in the Amhara region of Ethiopia.• IDSS analyses indicate that a significant improvement in family incomes and nutrition can be achieved through the adoption of farming technologies such as irrigation technologies and nutrient management.

Simulating grain yield and plant development of ratoon grain sorghum over diverse environments

Abstract Crop simulation may provide an inexpensive means to evaluate the feasibility of different cropping practices to optimize productivity and profitability. One practice, ratoon-cropping, may increase productivity and reduce per-unit production costs associated with conservation tillage farming systems in tropical and subtropical regions. sorkam , a dynamic plant growth model for grain sorghum [ Sorghum bicolor (L.) Moench], was used to evaluate the potential of rainfed ratoon grain sorghum over diverse climatic regions of Texas. Eleven independent data sets collected in the U.S.A. from sites in Georgia and Texas were used to determine the models accuracy. The model produced realistic estimates of grain yield for planted, ratoon, and combined (planted + ratoon) crops. Simulated grain yields usually were within 25% of the observed yield for the planted, ratoon, and combined crops with cultivars that produced the highest ratoon grain yield at each location. Ratoon grain yield results of multi-year simulations (10–30 years) from 14 locations over the eastern half of Texas using historic, location-specific, meteorological data indicated that the probability of obtaining ratoon grain yield > 3.0 Mg/ha was confined to the upper coastal plain region of Texas. The area best suited for rainfed ratoon grain sorghum appeared to be confined south and east of a line running from west of Corpus Christi to Beeville to College Station to west of Center, Texas. Use of crop models can play an important role in identifying strengths and weaknesses of potential cropping systems when used in combination with historical climatic data and/or computer weather generators.

Minimum Disturbance Fertilizer Knifing for No-Till

ABSTRACT SUBSURFACE application of fertilizer in no-till cropping systems to increase efficiency of use must be accomplished within constraints of minimum soil and crop residue disturbance. We evaluated a number of applicator knife and coulter combinations representative of those currently being used for this purpose. Applicator performance was measured as width of soil disturbed along the path of implement travel, as a function of soil penetration depth, travel speed, and soil water content. Width of soil disturbance increased on the average over all applicators, with an increase in each of these factors. Soil water content proved to be the more critical in light of its effect on adherence of the heavy clay soil to applicator surfaces. Applicators were ranked according to the amount of soil disturbance caused under each set of operating conditions. Rankings provided a means of relating the physical characteristics of applicators to relative level of performance, hence a guide in selecting adequate design criteria for their improvement.

EPIC Evaluation of the Impact of Poultry Litter Application Timing on Nutrient Losses

Recently, changes in the utilization practices of animal manures for fertilization have been encouraged to reduce the potential of nonpoint pollution of lakes and streams from agricultural land. However, the potential impact of changing some of these practices has not been fully studied. The objective of this study was to examine the potential impact of limiting poultry litter application times on nutrient movement important to water quality. The WinEPIC model was used to simulate poultry litter applications during the winter months and chemical fertilizer application, with both cool season and warm season grass pastures on the major soil regions of Alabama. With the warm season grass, soluble nitrogen (N) losses could be reduced if the application of poultry litter was made after 30 December. With the cool season grasses, there was no significant difference in application dates for poultry litter for soluble N losses for any soil region, and no improvement could be noted for limiting applications in northern Alabama compared to southern Alabama. No significant difference was observed for soluble phosphorus (P) losses for application date for either warm season or cool season grass pastures. This indicates that factors other than plant P uptake during the growing season were the dominant regulators of the amount of soluble P lost in runoff. Also, the results would indicate that best management practices such as are administered with the P index are more important than plant growth factors in determining N and P losses to the environment.