John J. Read

Corn (Zea mays L.) growth, leaf pigment concentration, photosynthesis and leaf hyperspectral reflectance properties as affected by nitrogen supply

Plant nitrogen (N)deficiency often limits crop productivity. Early detection of plant N deficiency is important for improving fertilizer N-use efficiency and crop yield. An experiment was conducted in sunlit, controlled environment chambers in the 2001 growing season to determine responses of corn (Zea mays L. cv. 33A14) growth and leaf hyperspectral reflectance properties to varying N supply. Four N treatments were: (1) half-strength Hoaglands nutrient solution applied throughout the experiment (control); (2) 20% of control N starting 15 days after emergence (DAE); (3) 0% N starting 15 DAE; and (4) 0% N starting 23 DAE (0% NL). Plant height, the number of leaves, and leaf lengths were examined for nine plants per treatment every 3–4 days. Leaf hyperspectral reflectance, concentrations of chlorophyll a, chlorophyll b,and carotenoids, leaf and canopy photosynthesis, leaf area, and leaf N concentration were also determined during the experiment. The various N treatments led to a wide range of N concentrations (11 – 48 g kg−1 DW) in uppermost fully expanded leaves. Nitrogen deficiency suppressed plant growth rate and leaf photosynthesis. At final harvest (42 DAE), plant height, leaf area and shoot biomass were 64–66% of control values for the 20% N treatment, and 46-56% of control values for the 0% N treatment. Nitrogen deficit treatments of 20% N and 0% N (Treatment 3) could be distinguished by changes in leaf spectral reflectance in wavelengths of 552 and 710 nm 7 days after treatment. Leaf reflectance at these two wavebands was negatively correlated with either leaf N (r = –0.72 and –0.75**) or chlorophyll (r = –0.60 and –0.72**) concentrations. In addition, higher correlations were found between leaf N concentration and reflectance ratios. The identified N-specific spectral algorithms may be used for image interpretation and diagnosis of corn N status for site-specific N management.

Rainfall simulation in greenhouse microcosms to assess bacterial-associated runoff from land-applied poultry litter.

Runoff water following a rain event is one possible source of environmental contamination after a manure application. This greenhouse study used a rainfall simulator to determine bacterial-associated runoff from troughs of common bermudagrass [Cynodon dactylon (L.) Pers.] that were treated with P-based, N-based, and N plus lime rates of poultry (Gallus gallus) litter, recommended inorganic fertilizer, and control. Total heterotrophic plate count (HPC) bacteria, total and thermotolerant coliforms, enterococci, staphylococci, Clostridium perfringens, Salmonella, and Campylobacter, as well as antibiotic resistance profiles for the staphylococci and enterococci isolates were all monitored in runoff waters. Analysis following five rainfall events indicated that staphylococci, enterococci, and clostridia levels were related to manure application rate. Runoff release of staphylococci, enterococci, and C. perfringens were approximately 3 to 6 log10 greater in litter vs. control treatment. In addition, traditional indicators such as thermotolerant and total coliforms performed poorly as fecal indicators. Some isolated enterococci demonstrated increased antibiotic resistance to polymixin b and/or select aminoglyocosides, while many staphylococci were susceptible to most antimicrobials tested. Results indicated poultry litter application can lead to microbial runoff following simulated rain events. Future studies should focus on the use of staphylococci, enterococci, and C. perfringens as indicators.

Leaf and canopy photosynthetic characteristics of cotton (Gossypium hirsutum) under elevated CO2 concentration and UV-B radiation

Increases in both atmospheric CO2 concentration ([CO2]) and ultraviolet-B (UV-B) radiation on the Earths surface are features of current climate change patterns. An experiment was conducted in sunlit, controlled environment chambers known as Soil-Plant-Atmosphere-Research (SPAR) units to determine interactive effects of elevated [CO2] and UV-B radiation on leaf and canopy photosynthetic characteristics of cotton. Six treatments were comprised of two CO2 levels of 360 (ambient) and 720 (elevated) microL L(-1) and three levels of 0 (control), 8, and 16 kJ m(-2) d(-1) biologically effective UV-B radiation. Treatments were imposed for 66 days from crop emergence through three weeks after the first flower stage. Plants grown in elevated [CO2] had significantly greater leaf area, higher leaf and canopy net photosynthetic rates (PN), lower dark respiration rate (Rd), and lower light compensation point (LCP) than plants grown in ambient [CO2]. There was no difference in CO2 compensation point (gamma), maximum rate of Rubisco activity (Vcmax), or light-saturated rate of electron transport (Jmax) between ambient and elevated CO2 treatments. When plants were grown in 8 kJ m(-2) d(-1) UV-B radiation, most of the measured photosynthetic parameters did not differ from control plants. High UV-B (16 kJ) radiation, however, caused 47-50% smaller leaf area, 38-44% lower leaf PN, 72-74% lower Vcmax, and 61-66% lower Jmax compared to the control. There were no interactive effects of [CO2] and UV-B radiation on most of the photosynthetic parameters measured. From the results, it is concluded that decreased canopy photosynthesis due to enhanced UV-B radiation in cotton is associated with both smaller leaf area and lower leaf PN, and loss of Rubisco activity and electron transport are two major factors in UV-B inhibition of leaf PN.

EFFECT OF MIXED-SALT SALINITY ON GROWTH AND ION RELATIONS OF A QUINOA AND A WHEAT VARIETY

ABSTRACT Salinity is among the most widespread and prevalent problems in irrigated agriculture. Many members of the family Chenopodiaceae are classified as salt tolerant. One member of this family, which is of increasing interest, is quinoa (Chenopodium quinoa Willd.) which is able to grow on poorer soils. Salinity sensitivity studies of quinoa were conducted in the greenhouse on the cultivar, “Andean Hybrid” to determine if quinoa had useful mechanisms for salt tolerant studies. For salt treatment we used a salinity composition that would occur in a typical soil in the San Joaquin Valley of California using drainage waters for irrigation. Salinity treatments (ECi ) ranging from 3, 7, 11, to 19 dS m−1 were achieved by adding MgSO4, Na2SO4, NaCl, and CaCl2 to the base nutrient solution. These salts were added incrementally over a four-day period to avoid osmotic shock to the seedlings. The base nutrient solution without added salt served as the non-saline control solution (3 dS m−1). Solution pH was uncontrolled and ranged from 7.7 to 8.0. For comparative purposes, we also examined Yecora Rojo, a semi-dwarf wheat, Triticum aestivum L. With respect to salinity effects on growth in quinoa, we found no significant reduction in plant height or fresh weight until the electrical conductivity exceeded 11 dS m−1. The growth was characteristic of a halophyte with a significant increase in leaf area at 11 dS m−1 as compared with 3 dS m−1 controls. As to wheat, plant fresh and dry weight, canopy height, and leaf area did not differ between controls (3 dS m−1) and plants grown at 7 dS m−1. Beyond this threshold, however, plant growth declined. While both quinoa and wheat exhibited increasing Na+ accumulation with increasing salinity levels, the percentage increase was greater in wheat. Examination of ion ratios indicated that K+:Na+ ratio decreased with increasing salinity in both species. The decrease was more dramatic in wheat. A similar observation was also made with respect to the Ca2+:Na+ ratios. However, a difference between the two species was found with respect to changes in the level of K+ in the plant. In quinoa, leaf K+ levels measured at 19 dS m−1 had decreased by only 7% compared with controls. Stem K+ levels were not significantly affected. In wheat, shoot K+ levels had decreased by almost 40% at 19 dS m−1. Correlated with these findings, we measured no change in the K+:Na+ selectivity with increasing salinity in quinoa leaves and only a small increase in stems. In wheat however, K+:Na+ selectivity at 3 dS m−1 was much higher than in quinoa and decreased significantly across the four salinity levels tested. A similar situation was also noted with Ca2+:Na+ selectivity. We concluded that the greater salt tolerance found in quinoa relative to wheat may be due to a variety of mechanisms.

Molecular and cytological characterization of a cytoplasmic-specific mutant in pima cotton (Gossypium barbadense L.)

A cytoplasmic mutant of Gossypium barbadense L., cyt-V was characterized at the morphological, cellular, genetic and molecular levels using comparison analysis with v7v7, a nuclear virescent mutant to identify molecular effects of the cyt-V mutation. The yellow phenotype was specific only to leaves in the cyt-V mutant (CM-1-90) but the same phenotype was present in both leaves and cotyledons of v7v7, a nuclear virescent mutant, suggesting that cyt-V and v7v7, had different organ-specific gene actions. Chlorophyll and carotenoid levels of CM-1-90, CM-1-90 × PS-7 and CM-1-90 × v7v7 true leaves were significantly lower than in the true leaves of PS-7 × CM-1-90, v7v7 × CM-1-90 and PS-7. Anatomical studies of chloroplast showed that CM-1-90, CM-1-90 × PS-7 and CM-1-90 × v7v7 lacked grana in the thylakoids of the mesophyll cells. This indicated that chlorophyll and carotenoid levels correlated with chloroplast structure. SDS-PAGE analysis of thylakoid preparations revealed decreases of several granalocalized PSII proteins in CM-1-90, CM-1-90 × PS-7 and CM-1-90 × v7v7. cDNA-AFLP differential display studies identified several differentially expressed transcripts in the leaves of reciprocal crosses (PS-7 × CM-1-90, v7v7 × CM-1-90 and CM-1-90 × PS-7 and CM-1-90 × v7v7), including one possessing a high sequence homology to a psbA gene. Western blot analysis further confirmed the absence of D1 protein encoded by psbA in CM-1-90 × PS-7′ CM-1-90 × v7v7 and CM-1-90 true leaves. Overall, we studied cyt-V and v7v7 that both are developmental mutants, as all the virescents of cotton mutants, and as such it was difficult to separate cause and effect in the observation; however, we verified that the source of cyt-V mutation was in chloroplast and elucidated that its gene action was different from v7v7. Results indicated that cyt-V is inherited as a single gene but it affects several chloroplast and nucleus-encoded genes. We identified several transcripts that associated with the cyt-V mutation. This study also suggested that chloroplast-encoded gene products might affect the expression of nuclear genes, possibly at the transcriptional stage.

Swine Effluent Application Timing and Rate Affect Nitrogen Use Efficiency in Common Bermudagrass

Bermudagrass [Cynodon dactylon (L.) Pers.] hay production is integral to manure management on southeastern swine farms. But swine effluent timing must be synchronized with crop nitrogen (N) demands to decrease the potential for soil N accumulation and nitrate (NO(3)) leaching. Field studies were conducted on a Prentiss sandy loam (coarse-loamy, siliceous, semiactive, thermic Glossic Fragiudult) to determine N-use efficiency (NUE) and residual soil NO(3)-N. Two rates of 10 and 20 cm yr(- 1) ( approximately 260 and 480 kg ha(-1) N, respectively) were applied in four timing treatments: April to September (full season), April to May, June to July, and August to September. Plots were harvested every 7 to 9 wk beginning in June, and soil was sampled in fall after a killing frost and the following spring. Annual uptake of N and P were least in the August to September timing treatment. Doubling the effluent rate increased N uptake 112% in 2000 (from 130 to 276 kg ha(-1)) and 53% in 2001 (from 190 to 290 kg ha(-1)), suggesting 10-cm did not meet crop N demands. Due to low rainfall and decreased forage yield in 2000, doubling the effluent rate led to increased soil NO(3)-N to 30-cm depth in fall 2000 and spring 2001. Averaged across timing treatments, soil NO(3)-N at 5-cm depth ranged from 8.5 mg kg(-1) in non-irrigated controls to 39.6 mg kg(-1) with 20-cm effluent. Results indicate low NUE in the order of 30 to 38% for applications in August to September increase the risk to surface and ground water quality from excess N remaining in soil.

Genotypic and environmental variation for carbon isotope discrimination in crested wheatgrass, a perennial forage grass.

Publisher Summary Crested wheatgrass, Agropyron desertorum, is a C 3 forage grass used extensively for revegetating deteriorated, semiarid rangelands in western North America. Crested wheatgrass is an important source of forage in early spring and autumn for both domestic livestock and wildlife. This chapter reviews work with crested wheatgrass and discusses the association of carbon isotope discrimination (Δ) with transpiration efficiency or water use efficiency (W), the effect of environment on Δ, the genotypic variation present for Δ, the stability of the Δ response, and the association between Δ and forage yield. The information about genotype by environment interactions or the consistency of genetic differences across environments is essential to an effective breeding program. In the chapter, to obtain such background data, the responses of Δ values of crested wheatgrass clones are evaluated under six environmental regimes in a tabulated form. The clone by environment interactions were not significant in three of the six instances, and simple correlation coefficients were always positive and usually significant.

Effects of bedding materials in applied poultry litter and immobilizing agents on runoff water, soil properties, and bermudagrass growth.

Poultry producers in the United States have begun using different types of bedding materials in production houses. Release into the environment of nutrients from applied poultry litter (PL) made with different bedding materials has not been investigated, and little information is available on nutrient concentrations in soils that receive broiler litter made with such materials. In this greenhouse study, two bedding materials (rice hulls and pine chips) in PL and two nutrient-immobilizing agents (gypsum and biochar) were applied to bermudagrass, and chemical and microbial contents of runoff water, soil properties, and plant growth were evaluated. Treatments with rice hull bedding material in PL had less runoff nutrient and greater soil soluble N and P compared with pine chip bedding. Gypsum and biochar both significantly reduced C, N, P, Cu, and Zn losses from the first runoff event, which were reduced by 26, 30, 37, 38, and 38% and by 25, 24, 30, 29, and 35%, respectively, but only gypsum obviously reduced these nutrients from later events. Potassium, Ca, Mg, and Mn increased by 2, 36, 11, and 9 times, respectively, and soluble P, Cu, and Fe significantly decreased by 68, 72, and 98%, respectively, in soil amended with gypsum. Rice hull PL in combination with gypsum significantly increased the growth of bermudagrass. Our results indicate that rice hull PL posed less risk for nutrient loss than pine chip PL when applied to fields and that gypsum was better than biochar for reducing runoff C, N, P, and Cu.

Remote-sensing algorithms for estimating nitrogen uptake and nitrogen-use efficiency in cotton

Abstract Nitrogen management is a major concern in high-yielding cotton (Gossypium hirsutum L.)-production systems. Objectives of this study were to investigate cotton leaf photosynthesis, plant growth, canopy spectral reflectance, and lint-yield responses to N application rate and to determine plant N uptake, partitioning, and use efficiency in Mississippi Delta, USA. Treatments included four N rates of 0, 56, 112, and 168 kg N ha−1. Increased N rate significantly affected cotton leaf photosynthetic rate, leaf area index, N concentrations of leaves and fruit, plant N uptake, and N-use efficiency, but had less effect on N partitioning among the plant tissues. Lint-yield response to N rate depended on soil N level and experimental year. Cotton plant shoot N concentration and N uptake significantly and linearly correlated with the selected ratios (R 715/R 405, r 2=0.65*** and R 795/R 755, r 2=0.70***, respectively) of canopy reflectance measured during the squaring and fruiting of plant development. Proper management of N application in cotton based on soil N analysis and plant N status could improve cotton N-use efficiency and lint yield. Remote-sensing algorithms, developed from canopy reflectance ratios in this study, may be used to estimate N concentration in cotton shoots and plant N uptake and help producers make cotton N-management decisions during the growing season.

A Model to Estimate Hydrological Processes and Water Budget in an Irrigation Farm Pond

With increased interest to conserve groundwater resources without reducing crop yield potential, more on-farm water storage ponds have been constructed in recent years in USA and around the world. However, the hydrological processes, water budget, and environmental benefits and consequences of these ponds have not yet been fully quantified. This study developed a computer model to estimate farm pond hydrological processes and water budgets using the STELLA (Structural Thinking and Experiential Learning Laboratory with Animation) software. The model was applied, as demonstrations, to estimate the diurnal and seasonal pond hydrological processes and water budget at Metcalf Farm (33o 39′ 48″ N, 90o 39′ 12″W) in Porter Bayou Watershed located in Mississippi Delta, USA. Two simulation scenarios were chosen in this study, one without and the other with pumping pond water for soybeans irrigation. Simulations showed that the evaporative loss of water from the pond was minimal, while the runoff water from rainfall was a major source of water entering into the pond. Therefore, factors that would affect surface water runoff should be considered in locating and sizing a farm pond in Mississippi. The seasonal rainwater and runoff water collected by the pond was: winter > spring > summer > fall, which corresponded well to the seasonal rainfall events; whereas seasonal order of pond evaporation was: summer > spring > fall > winter, which corresponded well to the seasonal solar radiation and air temperature. The STELLA model developed proved to be a useful tool for estimating pond water budget and consequently irrigation practices for crops.