Gretchen F. Sassenrath

Impaired reductive activation of stromal bisphosphatases in tomato leaves following low-temperature exposure at high light

Photosynthesis in domestic tomato (Lycopersicon esculentum L.) is highly sensitive to low temperature, particularly when accompanied by high light. Since previous studies have established that the inhibited plants retain photosynthetic electron transfer and ATP formation competence, we sought to identify specific steps in the photosynthetic carbon reduction pathway that could account for the lost photosynthetic capacity. Measurements of steady-state photosynthetic metabolite pool sizes showed an accumulation of fructose 1,6-bisphosphate and sedohepulose 1,7-bisphosphate following chilling in the light. Measurements of in vivo turnover rates of the metabolite pools accompanied by direct determinations of enzymatic activity showed that the capacity of the stromal bisphosphatases was substantially reduced following chilling in the light and was the cause of the bisphosphate accumulation. The time course of the loss of phosphatase activity closely mimicked that of the inhibition of net photosynthesis, further indicating that impaired phosphatase function is the underlying cause of the sensitivity of photosynthesis in tomato to light and chilling. Fructose 1,6-bisphosphatase extracted from inhibited tomato plants could be fully activated in the presence of dithiothreitol, indicating that chilling in the light disrupts the normal, thioredoxin-dependent, activation pathway of the stromal bisphosphatases. This disruption could involve a change in the redox potential of the functional disulfide on the phosphatases.

Technology, complexity and change in agricultural production systems

Technological advances have contributed to impressive yield gains and have greatly altered US agriculture. Selective breeding and directed molecular techniques address biological shortcomings of plants and animals and overcome environmental limitations. Improvements in mechanization, particularly of power sources and harvest equipment, reduce labor requirements and increase productivity and worker safety. Conservation systems, often designed to overcome problems introduced from other technologies, reduce negative impacts on soil and water and improve the environmental sustainability of production systems. Advances in information systems, largely developed in other disciplines and adapted to agriculture, are only beginning to impact US production practices. This paper is the fourth in the series of manuscripts exploring drivers of US agricultural systems. While development of technology is still largely driven by a need to address a problem, adoption is closely linked with other drivers of agricultural systems, most notably social, political and economic. Here, we explore the processes of innovation and adoption of technologies and how they have shaped agriculture. Technologies have increased yield and net output, and have also resulted in decreased control by producers, increased intensification, specialization and complexity of production, greater dependence on non-renewable resources, increased production inputs and hence decreased return, and an enhanced reliance on future technology. Future technologies will need to address emerging issues in land use, decline in work force and societal support of farming, global competition, changing social values in both taste and convenience of food, and increasing concerns for food safety and the environment. The challenge for farmers and researchers is to address these issues and develop technologies that balance the needs of producers with the expectations of society and create economically and environmentally sustainable production systems.

Environment and integrated agricultural systems

Modern agriculture has done an excellent job producing food, feed and fiber for the worlds growing population, but there are concerns regarding its continued ability to do so, especially with the worlds limited resources. To adapt to these challenges, future agricultural systems will need to be diverse, complex and integrated. Integrated agricultural systems have many of these properties, but how they are shaped by the environment and how they shape the environment is still unclear. In this paper, we used commonly available county-level data and literature review to answer two basic questions. First, are there environmental limitations to the adoption of integrated agricultural systems? Second, do integrated agricultural systems have a lower environmental impact than more specialized systems? We focused on the Great Plains to answer these questions. Because of a lack of farm-level data, we used county-level surrogate indicators. The indicators selected were percent land base in pasture and crop diversity along a precipitation gradient in North Dakota, South Dakota, Nebraska and Kansas. Evaluated over the four-state region, neither indicator had a strong relationship with precipitation. In the Dakotas, both percent pasture land and crop diversity suggested greater potential for agricultural integration at the mid-point of the precipitation gradient, but there was no clear trend for Kansas and Nebraska. Integrated agricultural systems have potential to reduce the impact of agriculture on the environment despite concerns with nutrient management. Despite advantages, current adoption of integrated agricultural systems appears to be limited. Future integrated agricultural systems need to work with environmental limitations rather than overcoming them and be capable of enhancing environmental quality.

Effect of Chilling on the Activity of Enzymes of the Photosynthetic Carbon Reduction Cycle

Photosynthesis measured at the normal growth temperature for the chill-sensitive tomato is inhibited by 60% after plants experience a 1 °C cold treatment in the dark for 16 hours. While s tomatal closure is responsible for a portion of this reduction, the principle component of the injury is due to a direct inhibition of chloroplast activity (1). Other chill-sensitive species show a similar response, and it seems likely that in general approximately 2/3 of the chill-induced decrease of photosynthesis is due to an inhibition at the chloroplast level (2). The capacity for electron transport and ATP synthesis is not significantly reduced following a dark chilling treatment (3, 4). Therefore, the reduction in photosynthetic rate measured at saturating light and CO2 probably cannot be accounted for by an inhibition of the membrane-associated reactions. The damage to photosynthesis that occurs under conditions of high light and cold temperatures is even more severe than chilling temperatures alone, resulting in more than a 50% reduction in chloroplast activity after only 6 hours (5). The mechanism of injury may be completely different than that observed after chilling in the dark, or the increased damage may arise from additional injury incurred by high light at cold temperatures.

Current irrigation practices in the central United States reduce drought and extreme heat impacts for maize and soybean, but not for wheat

In this study, we assessed the adaptive effects of irrigation on climatic risks for three crops (maize, soybean, and wheat) at the regional scale from 1981 to 2012 in the Central US. Based on yields of 183 counties for maize, 121 for soybean and 101 for wheat, statistical models were developed for irrigated, rainfed and county-level yields. Results show that irrigation has a statistically significant effect on abating detrimental climate impacts, specifically drought and extreme heat, in maize and soybean but not in wheat. On average, irrigation reduces the negative influences of extreme heat by around 7.2% for maize and 5.0% for soybean yields for each additional 10 degree-days above the optimal temperature for each crop. This is approximately two-thirds of the negative effects of extreme heat under rainfed management. The remaining third of the yield reduction is caused by heat damage that cannot be alleviated by irrigation. No significant differences were detected between county yields and irrigated yields for maize and soybean, suggesting that the existing irrigation practices were reasonably efficient. Efforts to mitigate future climate risks for these two crops should focus on improving the heat sensitivity contributing to the yield losses from heat damage. In contrast, the existing irrigation does not improve the resilience of wheat to climate risks. Both increased temperature and drought were critical to wheat production, which was potentially caused by relatively poor irrigation supplies for wheat. Further enhancement of wheat yield may be possible through improved irrigation management.

RAPID SAMPLING SYSTEM FOR DETERMINATION OF COTTON FIBER QUALITY SPATIAL VARIABILITY

The introduction of accurate, reliable cotton yield monitors has increased the value of spatial information pertaining to cotton growth and yield potential, and has contributed to the development and incorporation of site-specific methodologies into cotton production systems. While knowledge of the spatial variability of cotton yield is important for developing profitable management strategies, cotton quality also contributes to the net return. Cotton fiber is graded for several properties, including physiological maturity. The price of the cotton is then derived from the measured fiber quality. Variability in cotton yield contributes substantially to differences in profitability from various regions within production fields. Variability in fiber quality parameters will contribute additional alterations in the profitability of field regions. Currently, the determination of spatial patterns of fiber quality is performed by hand-harvesting areas of research or production fields. While this provides some measure of the degree and extent of variability in fiber properties, hand harvesting is tedious, time consuming, and error prone. Moreover, hand-harvested cotton displays distinct differences in fiber properties from that harvested mechanically. The time and labor commitment to adequately sample a large production field makes hand harvesting untenable for rapid and accurate determination of spatial patterns of fiber quality. Our research examines the spatial variability of fiber quality and quantity, with an end to delineating the underlying parameters contributing to that variability. To adequately address the variability of fiber production, we needed an accurate, rapid method of spatially sampling seed cotton for determination of lint properties. Moreover, to assure similarity between our measures of cotton fiber properties and those received by the producer or the gin, we needed a method of sampling the cotton after it had been mechanically harvested. We developed a sampling system that attaches to the transfer chute of the cotton harvester. The sampling system diverts the harvested cotton from the picker basket to a small sampling bag, allowing rapid subsampling of the harvested cotton in a spatially registered location. The sampling system has been tested for two harvest seasons, and found to be a reasonable method to measure the spatial variability of cotton fiber.

New insights into phosphorus management in agriculture — A crop rotation approach

This manuscript presents research results examining phosphorus (P) management in a soil–plant system for three variables: i) internal resources of soil available phosphorus, ii) cropping sequence, and iii) external input of phosphorus (manure, fertilizers). The research was conducted in long-term cropping sequences with oilseed rape (10 rotations) and maize (six rotations) over three consecutive growing seasons (2004/2005, 2005/2006, and 2006/2007) in a production farm on soils originated from Albic Luvisols in Poland. The soil available phosphorus pool, measured as calcium chloride extractable P (CCE-P), constituted 28% to 67% of the total phosphorus input (PTI) to the soil–plant system in the spring. Oilseed rape and maize dominant cropping sequences showed a significant potential to utilize the CCE-P pool within the soil profile. Cropping sequences containing oilseed rape significantly affected the CCE-P pool, and in turn contributed to the P(TI). The P(TI) uptake use efficiency was 50% on average. Therefore, the CCE-P pool should be taken into account as an important component of a sound and reliable phosphorus balance. The instability of the yield prediction, based on the P(TI), was mainly due to an imbalanced management of both farmyard manure and phosphorus fertilizer. Oilseed rape plants provide a significant positive impact on the CCE-P pool after harvest, improving the productive stability of the entire cropping sequence. This phenomenon was documented by the P(TI) increase during wheat cultivation following oilseed rape. The Unit Phosphorus Uptake index also showed a higher stability in oilseed rape cropping systems compared to rotations based on maize. Cropping sequences are a primary factor impacting phosphorus management. Judicious implementation of crop rotations can improve soil P resources, efficiency of crop P use, and crop yield and yield stability. Use of cropping sequences can reduce the need for external P sources such as farmyard manure and chemical fertilizers.

Nitrogen balance as an indicator of environmental impact: Toward sustainable agricultural production

Efficient nutrient use is critical to ensure economical crop production while minimizing the impact of excessive nutrient applications on the environment. Nitrogen (N) is a key component of agricultural production, both as an input to support crop production and as a waste product of livestock production. Increasing concern for future sustainability of agricultural production and preservation of the natural resource base has led to the development of nutrient budgets as indicators and policy instruments for nutrient management. Nutrient budgets for N have been developed by the Organization for Economic Co-operation and Development (OECD) as agri-environmental indicators to compare the evolving conditions in member states, and are also used by the US Department of Agriculture Natural Resource Conservation Service (USDA-NRCS) to develop nutrient management plans. Here, we examine the crop and animal production systems, drivers impacting management choices, and the outcome of those choices to assessthe utility of gross annual N balances in tracking the progress of management decisions in minimizing the environmental impact of agricultural production systems. We use as case studies two very different agronomic production systems: Mississippi, USA and Poland. State and country level datafrom the US Department of Agriculture and OECD databases areused to develop data for the years 1998–2008, and gross annual N balances are computed. Examination of agricultural production practices reveals that the gross annual N balance is a useful tool in identifying differences in the magnitude andtrendsinNwithinagriculturalsystemsoverlargeareas.SignificantdifferencesinthemagnitudeoftheNbudgetwere observed between the highly diversified, small-scale agriculture common to Poland, and the large-scale, intensive agriculture of Mississippi. It is noted that use of N balance indices can be problematic if the primary intent isto reveal the impact of economic drivers, such as crop prices, or management choices, such as tillage or crop rotation. Changes in cropping systems in response to commodity prices that improve N balance can be masked by detrimental growing conditions, including edaphic, biotic and weather conditions, that are outside of the producers’ control. Moreover, use of large area-scale indices such as country or state-wide balances may mask the severity of localized nutrient imbalances that result from regionalized production systems that overwhelm the nutrient balance, such as confinement livestock production. Development of a policy to address environmental impact and establish sustainable production systems must consider the year-to-year variability of drivers impacting agricultural production, and the spatial heterogeneity of nutrient imbalance.

Relationships between water table and model simulated ET

This research was conducted to develop relationships among evapotranspiration (ET), percolation (PERC), groundwater discharge to the stream (GWQ), and water table fluctuations through a modeling approach. The Soil and Water Assessment Tool (SWAT) hydrologic and crop models were applied in the Big Sunflower River watershed (BSRW; 7660 km(2) ) within the Yazoo River Basin of the Lower Mississippi River alluvial plain. Results of this study showed good to very good model performances with the coefficient of determination (R(2) ) and Nash-Sutcliffe efficiency (NSE) index from 0.4 to 0.9, respectively, during both hydrologic and crop model calibration and validation. An empirical relationship between ET, PERC, GWQ, and water table fluctuations was able to predict 64% of the water table variation of the alluvial plain in this study. Thematic maps were developed to identify areas with overuse of groundwater, which can help watershed managers to develop water resource programs.

Development of irrigation scheduling tools for the humid, high-rainfall environment of the Lower Mississippi Delta

Irrigation in hot, humid areas is particularly challenging because irrigation must be applied in a timely manner to prevent yield loss due to crop water stress, yet avoid flooding should a rain event follow irrigation. Moreover, it is difficult to detect the onset of crop water stress under environmental conditions that limit evaporative cooling. The goal of this project is to develop reliable, easy to use irrigation scheduling tools that integrate crop monitoring and accurate weather predictions to improve the timing and application of irrigation in humid, high rainfall environments for better water management. The irrigation decision support system is based on calculations of crop water use from weather data collected from weather stations throughout Mississippi using crop coefficients developed from weighing lysimeters and other sources. A water balance approach is used to indicate when supplemental irrigation is needed based on available water and crop water use. This is integrated with other publicly available, spatially registered farm and soil databases to develop specific irrigation scheduling recommendations. A web-based interface is being developed to deliver the irrigation decision support system to producers through an easy to use and readily accessible format. Training materials will be developed and presented to producers through on-site training and other standard Extension mechanisms.