Jerry M. Bennett

Interactive effects of nitrogen and water stresses on biomass accumulation, nitrogen uptake, and seed yield of maize☆

Abstract Although considerable data exist on the growth, development, and productivity of crops in response to nutrients or water applied alone, much less data are available to describe the interactive effects of water and nitrogen. The objective of this study was to determine the interactive effects of N fertilizer and water on biomass (dry-matter) accumulation, N-uptake, and seed yield of maize (Zea mays L.) growing on sandy soils. Field-grown maize was subjected to three water management treatments: (1) optimal irrigation; (2) a 10-day wilting period immediately preceding silking (vegetative stress); and (3) rainfed. Within each water management treatment, two N treatments were imposed: (1) low N, consisting of a total of 11.6 g N M−2 applied in three side-dress applications; and (2) high N, consisting of a total of 40.1 g N m−2 applied in six side-dress applications. The effects of water and N stress on the crop were determined by growth analysis and measurements of N uptake made throughout the growing season. 3ow soil N significantly reduced leaf area as a result of reduced leaf size, but had little effect on the final number of leaves produced. However, both water and N stress lengthened the time from emergence to tasseling and silking. Accumulation rates of total biomass, seed weight, and N showed interactions with water and N. With high N, the 10-day wilting period preceing silking reduced biomass and seed yields by 22% and 19%, respectively, while the rainfed treatment resulted in 66% and 75% reductions. Low N also reduced biomass and seed yields in both the optimal irrigation and vegetative stress treatments. However, with severe water stress, N level had no effect on total crop biomass, N accumulation, or grain yields. When high N levels were applied, water stress reduced the efficiency of N utilization. With high N, crop N uptake in the optimal irrigation, vegetative stress, and rainfed treatments amounted to 67%, 53%, and 26% of that applied, respectively. With low N, the optimal irrigation and vegetative stress treatments accumulated N amounts near that applied. When severe water stress was imposed in combination with low N, only 60% of the applied N was accumulated by the crop. Nitrogen deficiency did not improve drought resistance of field-grown maize, as has sometimes been suggested.

Water relations, nitrogenase activity and root development of three grain legumes in response to soil water deficits

Abstract Because of the importance of dinitrogen (N 2 ) fixation and its relation to leaf photosynthesis and dry-matter accumulation in grain legumes, a field study was conducted in 1984 to compare the relative abilities of three grain legumes to maintain N 2 fixation rates under well-defined soil water deficits imposed in field environments. Measurements of leaf water status, root distribution and nitrogenase activity were determined on peanut ( Arachis hypogaea L.), soybean ( Glycine max L. Merr.), and pigeon pea ( Cajanus cajan L.) throughout the growing season. The three crops were grown in a Kendrick fine sand (loamy, siliceous, hyperthermic family of Arenic Paleudults) and subjected to two water management treatments: 1) an irrigated treatment which was well-watered throughout the growing season: and 2) a water-stressed treatment which was subjected to several naturally-occurring water-deficit periods. During periods of mild and moderate water stress, peanut maintained higher leaf water potentials and stomatal conductance than either soybean or pigeon pea. When well-watered, peanut also maintained considerably higher rates of specific nitrogenase activity than either soybean or pigeon pea. However, nitrogenase activity was reduced in all three crops before visible symptoms of water stress (leaf wilting) were apparent. Peanut maintained nitrogenase activity longer after withholding irrigation than either soybean or pigeon pea. Root distribution measured 68 days after emergence suggested that root length density of peanut at soil depths below 30 cm increased in response to the imposed water deficits. Proliferation of roots in those soil layers as a result of water stress was not observed in either soybean or pigeon pea. The maintenance of higher leaf water-status, stomatal conductance and nitrogenase activity by peanut during soil water deficits compared to the other crops was attributed to greater density of roots in the lower depths of the soil profile.

Relationship of nitrogenase activity to plant water stress in field-grown soybeans☆

Abstract Soybeans are often subjected to periods of water deficits during ontogeny. Water stress can produce lower leaf water potentials, stomatal closure, decreased photosynthesis, and ultimately result in reduced yields. Although the responses of many physiological processes to water deficits have been extensively studied, the effects on nitrogen fixation, an important process for leguminous plants, have received little attention in field experiments. We conducted an experiment to relate the effects of reduced soil moisture on the nitrogenase activity of soybean nodules to changes in leaf water status, stomatal activity, nodule water content and apparent canopy carbon exchange during an imposed drying cycle. Field-grown soybeans were subjected to a 19-day drying cycle during early seed fill. At chosen intervals, midday measurements of selected physiological proceses were made in stressed and well-watered control plants. Leaf water potential, leaf conductance to water vapor, nodule moisture content, apparent carbon exchange and nitrogenase activity declined as the duration of the stress period increased. All physiological processes, except apparent canopy carbon exchange rate, returned to control levels upon adequate rewatering. The incomplete recovery of apparent carbon exchange was attributed to decreased leaf area index resulting from leaf senescence during the stress period. The data support the hypothesis that decreases in nitrogenase activity are primarily caused by nodule dehydration and tissue damage and not directly related to short-term changes in photosyntheses. It is apparent that nitrogenase activity declined similarly with other physiological processes, however, the observations did not conclusively define the precise relationships of nitrogenase activity to the other physiological processes.

Nitrogen accumulation and partitioning by three grain legumes in response to soil water deficits

Abstract Few experiments have been conducted to compare the partitioning and accumulation of nitrogen (N) in plant components of grain legumes grown under different soil water regimes. The objective of this study was to determine the effect of soil water deficit on N accumulation and partitioning in soybean ( Glycine max L. Merr.), pigeon pea ( Cajanus cajan L.), and peanut ( Arachis hypogaea L.). In 1984, the three legumes were subjected in a field environment to either well-watered or water-stressed treatments. Nitrogen concentration, total N accumulation, and N partitioning were determined throughout the growing season by measuring N content and concentration in leaves, stems, pod walls, and seeds. Peanut accumulated more total N than either soybean or pigeon pea under both the well-watered and water-stressed treatments. Water stress decreased both N concentration and total N accumulation, especially in soybean and pigeon pea. Less remobilization of N occurred in soybean leaves and stems during the seed-filling period in the stressed treatment because the water stress limited pod addition and subsequent seed demand for N. Loss of N from leaves during seed growth was greater in the crop with the most senescent growth habit (soybean), and lowest in the non-senescent but determinate crop (pigeon pea). Although peanut does not exhibit rapid leaf senescence during seed maturation as does soybean, considerable loss in leaf N was also observed in peanut leaves during the seed-filling period. Soy-bean, peanut, and pigeon pea differed in accumulation and partitioning of N under water-stressed and non-stressed environments. The partitioning and remobilization of N was dependent on the growth habit of the species and was significantly influenced by soil water deficits.

Reductions in a Commercial Potato Irrigation Schedule during Tuber Bulking in Florida: Physiological, Yield, and Quality Effects

Proper irrigation scheduling in potato (Solanum tuberosum L.) can lead to higher returns and more sustainable production practices when compared to systems that do not take plant water demand into account. In an attempt to reduce irrigation applications while minimizing yield reduction, we evaluated a novel deficit irrigation treatment utilizing a mild irrigation reduction during tuber bulking by comparing a typical commercial irrigation schedule to a partial irrigation schedule. Physiological, yield, and quality effects were quantified. Reducing the number of irrigation applications by 14 in 2011 and by 9 in 2012 minimally affected most parameters measured. However, a significant yield reduction of 11,713 kg/ha in the partial irrigation treatment occurred in 2011, likely because of the irrigation treatment commencing at the latter portion of tuber initiation. In 2012, the initiation of the partial irrigation was delayed and resulted in no significant difference in yield between the partial and full irrigation treatments. This study shows the potential for a reduced irrigation schedule for use by Florida potato growers as a sustainable option for potato production in this region.

Non-dehiscent sesame (Sesamum indicum L.): its unique production potential and expansion into the southeastern USA

ABSTRACT Sesame is a new crop for the southeastern USA, most recently being considered for this region because of frequent drought events in the historical farming area of the crop, that is, Texas and Oklahoma, and for overall expansion of its domestic production. Although sesame was introduced in the USA in the 19th century, its commercial cultivation was not possible before the 1990s with the release of non-dehiscent cultivars. The southeastern USA has been considered promising because of its greater annual precipitation as compared with the southwestern USA. In addition, sesame has some highly valuable agronomic characteristics that could make the crop a beneficial addition to crop rotations in the southeast. These crop characteristics include the following: nematode resistance potential, drought tolerance, nitrogen recovery ability, rotational suitability with the predominant agronomic crops in the region, and capacity to attract a wide variety of pollinators. Since very little United States-based literature is available on the crop, the objective of this review is to provide: 1) a sesame history in the USA; 2) a description of the botanical characteristics of the crop that make it suitable for mechanized production in the USA; and 3) an overview of the principal sesame production methods of interest for the southeastern USA.

Visualization of Peanut Nodules and Seasonal Nodulation Pattern in Different Tillage Systems Using a Minirhizotron System

ABSTRACT Nodulation is essential for providing the nitrogen (N) needs of peanut, but little is known about the time course of nodule development with soil depth in a field production system. A minirhizotron system allows for non-destructive, periodic digital imaging of identical locations in the crop root system in situ, including the associated nodules. Because the system allows imaging at the same location over time, individual nodule development and subsequent senescence can be followed throughout the growing season. To test the proof of concept for the use of a minirhizotron system to observe peanut nodule development, a case study was conducted in 2012 in Citra, FL in a sod-based production system managed with both conservation and conventional tillage at two different timings. Images were taken to a soil depth of 90 cm on four dates during the growing season, and nodule number, surface area, and senescence were determined. Most nodules occurred at depths spanning 5-30 cm with very few outside of thi...

Rotating peanut into established bahiagrass pastures: identifying sustainable tillage operations

ABSTRACT Integrating bahiagrass (Paspalum notatum Flueggé) into peanut (Arachis hypogaea L.) production systems can improve soil structure, and increase peanut yield. A study was conducted in 2012 and 2013 in north Florida to evaluate practices for planting peanut into bahiagrass with three tillage methods i.e.; strip till (ST), ST and high residue cultivation (ST/HRC), and conventional (CT) tillage. Tillage times were 30 d before planting (DATE1) and at planting (DATE2). Peanut grown under CT outyielded ST/HRC (6940, 6580, and 6370 kg ha−1 for CT, ST, and ST/HRC, respectively), but there was no difference in economic return across treatments (adjusted revenue avg. = US

The Relationship Between Sap Flow and Commercial Soil Water Sensor Readings in Irrigated Potato (Solanum tuberosum L.) Production

2478 ha−1). Tillage DATE2 increased total root length compared with DATE1, particularly for CT and ST. The ST/HRC had increased total root length below 30 cm for DATE1. When peanut was planted into bahiagrass, conservation tillage practices maintained adjusted revenue comparable with CT while providing environmental benefits.

Temperature and solar radiation effects on potential maize yield across locations

Many irrigation scheduling methods utilized in commercial production settings rely on soil water sensors that are normally purchased as off-the-shelf technology or through contracted services that install and monitor readings throughout the season. These systems often assume a direct relationship between the parameters measured by these soil water sensors (voltage, unitless values, or calibrated soil moisture values) and the water use and deficit stress of the crop. Because of this assumed relationship, these sensors are purported to be useful for triggering irrigation applications by monitoring relative changes in sensor values that represent either a “dry” or “wet” condition in the field. However, there is often little confirmation that these sensors accurately reflect crop water uptake or what soil depths will best represent that relationship. In an attempt to quantify the association between the use of soil water sensors and crop water use in a commercial potato field, measurements of soil water using capacitance probes and plant water use using sap flow sensors were monitored. Measurements were taken in two water application treatments: a normal (full) and partial irrigation schedule because it was hypothesized that the relative strength of the relationship between sensor reading and crop water use may be highly dependent on field soil water status. Relative soil moisture readings and plant water use data were compiled and both linear and quadratic regressions were performed. The correlation between sap flow and soil sensor readings was significant; but the relationship was relatively weak with the strength dependent on the soil depth that was monitored, indicating that care must be taken when utilizing sensor readings for irrigation scheduling.ResumenMuchos métodos de programación de riego que se utilizan en instalaciones de producción comercial se respaldan en sensores de agua en el suelo que generalmente se compran como tecnología “fuera de la plataforma” o a través de servicios contratados que instalan y le dan seguimiento a las lecturas a lo largo del ciclo. Estos sistemas con frecuencia asumen una relación directa entre los parámetros medidos por estos sensores de agua en el suelo (voltaje, valores sin unidades, o valores calibrados de la humedad del suelo) y el uso del agua y el agobio por déficit del cultivo. Debido a esta asumida relación, estos sensores son formalmente útiles para disparar aplicaciones de riego mediante el monitoreo de los cambios relativos en los valores del sensor que representan ya sea una condición “seca” o “húmeda” en el campo. No obstante, a menudo hay poca confirmación de que estos sensores reflejan con precisión la absorción del agua por el cultivo o a que profundidades del suelo representarán mejor esa relación. En un intento para cuantificar la asociación entre el uso de los sensores del agua del suelo y el uso del agua por el cultivo en una siembra comercial de papa, se dio seguimiento a las mediciones del agua en el suelo utilizando sondas de capacitancia y el uso de agua por la planta con sensores de flujo de savia. Se tomaron las mediciones en dos tratamientos de aplicación de agua: una programación normal (completa) y otra parcial de riego, porque se tuvo la hipótesis de que la fuerza relativa de la relación entre la lectura del sensor y el uso de agua por el cultivo pudiera ser altamente dependiente de la situación del agua del suelo en el campo. Se recopilaron datos de las lecturas de la humedad relativa del suelo y del uso de agua por la planta y se les hicieron regresiones lineales y cuadráticas. La correlación entre el flujo de savia y las lecturas de los sensores del suelo fue significativa primero bajo condiciones de agua limitada en el suelo; pero la relación fue relativamente débil con la fuerza dependiente de la profundidad del suelo que se monitoreó, indicando que se debe tener cuidado cuando se utilicen lecturas de sensores para la programación del riego.