Showing papers in "Agronomy Journal in 1987"

Nitrogen cycling in a wheat crop: soil, plant, and aerial nitrogen transport

Abstract: An understanding of N cycling in the soil-plant-atmosphere components of wheat (Triticum aestivum L.) production systems is necessary to maximize yield and quality. The objectives of this study were to examine N cycling and observe the effects of N surplus and deficit on N absorption/desorption in the soil and atmosphere and to evaluate translocation within the plant. Soil, plant, and microclimate measurements were taken concurrently, and soil, plant, and atmospheric ammonia (NH₃) transport determined. During the early vegetative phase, plant N concentration reached a maximum; however, during the remaining growth periods, N concentration decreased even though N uptake from the soil continued until plant maturity. More total N was translocated to grain from leaves than stems, and translocation from the leaves began earlier than that from stems. Isotope and total N studies showed that after anthesis about half of the grain N came from remobilization from leaves and stems and the other half directly from the soil. A progressively larger percentage of N came from mineralized organic matter as the season progressed. Nitrogen was lost as volatile NH₃ from the plant after fertilizer application and during the senescence period. Prior to anthesis, atmospheric NH₃ absorption was observed during a period when soil N was temporarily unavailable. About 21% equivalent of the applied fertilizer was lost as volatilized NH₃. During the period of soil unavailability an amount equivalent to about 1% equivalent of the applied fertilizer was gained from atmospheric NH₃ by plant absorption.

Mineral analysis of forages with near infrared reflectance spectroscopy

Abstract: Mineral concentration data could easily be generated by near infrared reflectance spectroscopy (NIRS) while determining quality parameters in forage samples. However, which minerals can be analyzed and why they can be determined has not been documented adequately. Therefore, NIRS spectra were collected on 200 samples of crested wheatgrass (Agropyron spp.), 203 tall fescue (Festuca arundinacea Schreb.), and 59 alfalfa (Medicago sativa L.) hays. Concentrations of Na, K, Ca, P, Mg, Fe, Mn, Cu, and Zn, as determined by atomic absorption, and calculated values of the Ca/P, K/Mg, and K/(Ca + Mg) ratios were regressed against reflectance values measured in 2-nm increments between 1100 and 2500 nm for each sample. Approximately one half of the samples in each forage set was used to develop the calibration equations, while the other half was used to validate the equations. The coefficients of variation [CV = (standard error of analysis ÷ the mean)X 100] generally ranged from 10 to 20% for K, Mg, Ca, and P concentrations in each forage type. The Ca/P ratio in alfalfa was determined with a CV of 18%. The CV values of other minerals and mineral ratios generally exceeded 20%. Chlorophyll and some inorganic salts and organic-acid salts of Ca, Mg, and K were scanned with NIRS for wavelength comparisons with those wavelengths used to determine mineral concentrations in forages. Some of the wavelengths used in the equations for Ca, K, and Mg were related to peaks and changes in slope observed in chlorophyll and organic-acid salts of Ca, K, and Mg, suggesting that NIRS is indirectly measuring these minerals by their association with organic molecules. Accurate use of NIRS to determine mineral cation composition in forages appears limited to certain major minerals (Ca, P, K, and Mg).

Contributions of Ground Cover, Dry Matter, and Nitrogen from Intercrops and Cover Crops in a Corn Polyculture System1

Abstract: Continuous corn (L.) grown on sloping land and harvested for silage, returns few residues to the soil and leaves the soil unprotected against erosion for most of the year. Three field experiments were conducted on a Lima loam (a fine-loamy, mixed, mesic Glossoboric Hapludalf) to determine the contributions from various intercrops and cover crops towards ground cover, dry matter, and N. In Exp. 1 and Exp. 2, the effects of intercrops and cover crops were measured by determining corn grain yields following the plow down of the various crops. Corn grain yields following the incorporation of various crops were compared to yields of corn where no cover crops had been incorporated but N rates of 0, 56 or 112 kg ha had been applied. In Exp. 3, the effects of intercrops and cover crops on corn yields were measured over a 5-yr period. First-year corn grain yields were neither increased nor decreased as a result of seeding intercrops when the corn was 0.15 to 0.30 m high. All intercrop and cover crop treatments in Exp. 3 provided significantly more ground cover than the control treatment. Annual ryegrass (Lam.), medium red clover (L.), and a combination of the two were the most effective in terms of ground cover and dry matter production.

Water Deficit Effects on Transpiration and Leaf Growth1

Abstract: Reductions of leaf development and transpiration are closely related to soil water deficits. Few studies have analyzed the effects of water deficits on both processes during different growth stages. A study was conducted to analyze and quantify the effects of water deficits during different growth stages on leaf development (number, extension, and senescence) and transpiration rates of sorghum [Sorghum bicolor (L.) Moench] and cotton (Gossypium hirsutum L.). The study was conducted a t the Blackland Research Center at Temple, TX, in a glasshouse using covered pots and in the field using covered lysimeters. In the glasshouse, the sorghum and cotton preflowering treatments were irrigated a t 60, 35, 15, and 0% of water used in the control pots. In the lysimeters, water deficit treatments of 50, 30, and 0% plant available water (PAW) were imposed on sorghum during the vegetative period (before panicle initiation and between panicle initiation and anthesis) and after anthesis. Leaf length and transpiration rates were measured two to three times per week. Leaf extension was reduced to 0% of well-watered sorghum and cotton when the PAW decreased from 50 to 0%. Transpiration per unit leaf area decreased from 100 to 0% of well-watered sorghum and cotton when PAW decreased from 28 to 0% for each stressed period. Sorghum leaf senescence was enhanced and leaf number increased in the 0% PAW treatments compared to the well-watered and 30% treatments. These relationships of leaf development, transpiration, and PAW compare favorably with other published results. The PAW threshold values when each process is affected would be useful in developing criteria for scheduling irrigation and in improving the accuracy of crop growth models in estimating leaf development and transpiration. Additional index words: Sorghum, Cotton, Soil water deficit, Lysimeter, Dry matter, Plant available water, Leaf senescence, Growth stage. NUMBER of relationships have been published that A describe the effects of water deficit on leaf growth (LG) and transpiration (T) (Meyer and Green, 1980; Acevedo et al., 1971; Ritchie et al., 1972). The percentage of plant available water (PAW) has been used to describe water status when T and LG decrease from the potential rate (Ritchie et al., 1972; Meyer and Green, 1980; Rosenthal et al., 1977; Tanner and Jury, 1976). At low PAW, reductions in T are generally accompanied by increased stomatal resistance and decreased photosynthetic rates, dry matter accumulation, and economic yield (Y) (Turner, 1974). Many relationships have been developed comparing Y to T (Hanks 1974; Garrity et ai., 1982; Arkley, 1963). The sensitivity of Y to T relationships differ between growth stages, with the most sensitive period for sorghum [Sorghum bicolor (L.) Moench] being the early boot through anthesis growth stages when the potential number of seeds per panicle is determined (Eastin et al., 1983; Garrity et al., 1982; Meyers, et al. 1984; Vanderlip and Reeves, 1972; Whiteman and Wilson, 1965). I Contribution from the Texas Agric. Exp. Stn., Texas A&M Univ., College Station, TX 77843. Contribution no. TA-22156. Received I4,Nov. 1986. Research scientist, Blackland Res. Ctr., Texas Agric. Exp. Stn., P.O. Box 6 1 12, Temple, TX 76503-6 1 12; associate director, Georgia Agric. Exp. Stn., Griffin, GA 30212; soil scientist, U.S. Salinity Lab., USDA-ARS, Riverside, CA 92501; and director, Texas Water Resources Inst., Texas A&M Univ., College Station, TX 77843, respectively. Published in Agron. J. 79:1019-1026(1987)~ Generally, the most sensitive period for cotton (Gossypium hirsutum L.) yield is during peak flowering (Marani and Horowitz, 1963; Marani and Fuchs, 1964). Water deficits may also affect canopy development through effects on total leaf number and rates of individual leaf emergence from the whorl, and on leaf extension and senescence (Arkin et al., 1983). All of these components are important in determining the surface area available for transpiration and assimilate production (Meyers et al., 1984; Parameswara and Krishnasastry, 1982; El-Sharkawy et al., 1965). Acevedo et al. (1 97 1) and Hsiao et al. (1 976) found corn (Zeu mays L.) leaf extension to be more sensitive to water deficits than transpiration. Meyer and Green (1 98 1) found the lower limit of PAW for maximum soybean [Glycine mux (L.) Merr.] leaf extension to be approximately 25%. The lower threshold for maximum T is also a function of evapotranspiration and soil hydraulic conductivity (Slabbers, 1980). In spite of the abundant literature on water deficit effects on leaf extension, few studies have investigated more than one plant process during water deficits applied at different growth periods (Hsiao, 1973; Ritchie, 1981). The purpose of our study was twofold: (i) analyze and quantify the effects of water deficit on sorghum leaf number and senescence, and sorghum and cotton leaf extension, and (ii) analyze and quantify water deficit effects on transpiration before flowering in cotton and sorghum, and after flowering in sorghum. MATERIALS AND METHODS Glasshouse Study. During 1982, a study was conducted in a ventilated glasshouse at the Blackland Research Center at Temple, TX, using thirty 50-L pots filled with Fno silt loam (fine, montmorillonitic, thermic Cumulic Haplustoll) (75%) and peat moss (25%). The pots were covered with polyethylene plastic sheets fitted around the base of each plant stem and covered with dry sand to minimize soil evaporation. Holes were drilled at the bottom of the pots to allow for free water drainage. Before planting, each pot was irrigated until water drained freely from the bottom. Weight changes were measured every other day using a 700-kg load cell, and were taken as transpiration rates. After anthesis, total plant weight was measured after plants remained wilted for 4 days. The changes of plant weight between measurements were small compared to the pot weight changes such that it resulted in less than 2% error and was ignored in the analysis. Sorghum (cv. 100M) and cotton (cv. SP37-H) were planted in 15 pots on 1 July. After emergence, seedlings were thinned to two plants per pot. Adequate minerals to provide for growth throughout the season were supplied before planting. The area of individual green sorghum leaves (LA) was determined from measurements of leaf length (LL) and maximum leaf width (LW) every second day using Eq. [ 11 suggested by Stickler et al. (1961): LA = LL X LW X 0.75. Measurements were taken from leaf emergence in the whorl until the leaf ligule had appeared. Leaves were numbered from the first leaf at plant emergence (Leaf 1) to the flag leaf I11 1019 Published November, 1987

Forage nutritive value and palatability of perennial weeds.

Abstract: Knowledge of forage quality of individual weed species is essential for making sound management decisions regarding the control of weeds that invade alfalfa (Medicago sativa L.). Our objective was to determine the nutritive value and palatability of nine perennial forb and grass weeds in comparison to alfalfa and smooth bromegrass (Bromus inermis Leyss.). Field trials were conducted on a fine-silty over sandy skeletal, mixed, mesic Typic Hapludoll. We used a randomized complete block design with four replicates. Compared to alfalfa, smooth bromegrass and quackgrass [Agropyron repens (L.) Beauv.] consistently had more neutral detergent fiber (NDF), less crude protein (CP), and similar in vitro digestibility (IVDDM). Grasses consistently had more NDF than forbs. Nutritive value varied considerably among forbs. Jerusalem artichoke (Helianthus tuberosus L.), Canada thistle [Cirsium arvense (L.) Scop.], dandelion (Taraxamum officinale Weber in Wiggers), and perennial sowthistle (Sonchus arvnesis L.) had CP and IVDDM concentrations equal to or greater than those of alfalfa, while Jerusalem artichoke, dandelion, and curly dock (Rumex crispus L.) frequently had lower NDF concentrations than that of alfalfa. Forb weeds generally had lower palatability than alfalfa or smooth bromegrass, with several exceptions. Jerusalem artichoke, curly dock, hoary alyssum [Berreroa incana (L.) DC.], and Canada thistle were either completely or nearly completely rejected by grazing lambs (Ovis spp.). Palatability of a quackgrass biotype selected for wide leaves was equal or superior to smooth bromegrass and was equal to alfalfa in two of three trials. Common quackgrass consistently had lower palatability than smooth bromegrass or alfalfa. Because forage quality of perennial weeds varied considerably among species and was sometimes superior to that of alfalfa, we conclude that decisions on whether to implement weed control in established alfalfa should be specific for each situation

Differences in Drought Resistance between Two Corn Hybrids. II. Component Analysis and Growth Rates1

Abstract: Relatively little research has been conducted to evaluate differing responses to water stress among genotypes of the same species. The objective of this study was to identify differences in growth and development of plant parts resulting from water stress imposed on two corn (L.) hybrids that had been observed to differ in their sensitivity to water stress. During 1983 and 1984, two corn hybrids (Pioneer Brands 3192 and 3165) were subjected to three water management treatments: optimal irrigation, rainfed, and stress during vegetative (1983) or early reproductive (1984) growth. Growth analysis revealed few differences between hybrids for leaf area index, and crop and seed growth rates when well-watered or stressed during vegetative growth, except that hybrid 3192 showed more rapid early growth. When well-watered, grain yield of hybrid 3192 was the same (1983) or higher (1984) than grain yield of hybrid 3165. However, the two hybrids differed in their ability to resist severe water stress. The greater grain yield of hybrid 3165 in the rainfed treatment was associated with relatively smaller reductions in crop growth rate, total biomass accumulation, seed number, effective filling period, and harvest index with stress when compared to hybrid 3192. The greater crop growth rate and final biomass and grain yield of hybrid 3165 during severe stress most likely resulted from the maintenance of higher leaf water and turgor potentials and lower leaf diffusive resistances that were apparently mediated by higher root length densities in deeper zones of the soil profile as described in a companion paper.

Atmospheric Carbon Dioxide Enrichment Effects on Cotton Midday Foliage Temperature: Implications for Plant Water Use and Crop Yield1

Abstract: In an experiment designed to determine the likely consequences of the steadily rising carbon dioxide (CO2) concentration of Earth's atmosphere for the foliage temperature, water use, and yield of cotton (Gossypium hirsutum L. var. Deltapine-61) plants, cotton was grown out-of-doors at Phoenix, AZ, in open-top, clear-polyethylene-wall, CO2-enrichment chambers for three summers under mean daylight CO2 concentrations of 340, 500 and 640 μmol CO2 mol−1 air on an Avondale clay loam soil [fine-loamy, mixed (calcareous), hyperthermic Anthropic Torrifluvent). Infrared thermometer measurements of the cotton foliage temperature (TF) indicated that a 330 to 660 μmol CO2 mol−1 air doubling of the atmospheric CO2 content results in a midday T, increase of 1.1 °C for well-watered cotton at Phoenix in the summer. This temperature increase was predicted to produce a 9% reduction in per-unit-leaf-area plant transpiration rate and an 84% increase in crop biomass production, which compared favorably with the measured crop biomass increase of 82% for such a doubling of the air's CO2 content. These findings, together with similar findings for a second plant species—water hyacinth [Eichhornia crassipes (Mart.) Solms]—allowed us to develop a technique for assessing the effects of a 330 μmol CO2 mol−1 air CO2 concentration increase on the percentage yield increase (Y) of a crop via infrared thermometry by means of the equation Y = 7.6% × (IJ)−1, where IJ represents the Idso-Jackson plant water stress index. If this equation holds up under further scrutiny, it could provide a rapid and efficient means for assessing the yield response of crops to atmospheric CO2 enrichment.

Dry Matter, Nitrogen, Phosphorus, and Potassium Accumulation Rates by Corn on Norfolk Loamy Sand1

Abstract: The maximum amount and rate of nutrient accumulation by irrigated corn (L.) must be known so that farmers do not waste money or pollute water resources by applying excessive amounts of fertilizer. Aerial whole plant samples were therefore collected from irrigated field experiments conducted on Norfolk (Typic Paleudults) loamy sand in 1980, 1981, and 1982, to determine seasonal dry matter, N, P, and K accumulations for corn yielding 10 Mg ha or more in the southeastern Coastal Plain. Rates of accumulation were derived by differentiating compound cubic polynomial equations that described seasonal accumulation patterns. Total dry matter accumulation averaged 23.1 and 24.9 Mg ha for two population treatments that averaged 7 ✕ l0 or 10 ✕ l0 plants ha. Aerial N, P, and K accumulation respectively averaged 228,58, and 258 kg ha in 1980; 264,37, and 372 kg ha in 1981; and 225,37, and 335 kg ha in 1982. Grain yields averaged 13.4, 11.7, and 10.9 Mg ha in 1980, 1981, and 1982, respectively. Lower P accumulations in 1981 and 1982 were the result of lower grain yields that were apparently caused by excessive K accumulation. Calculated peak dry matter, N, P, and K accumulation rates were 650, 10, 1.6, and 28 kg ha day in this study, compared to rates of 247,4.5,0.6, and 3.2 kg ha, respectively, in previous midwestern studies. Peak accumulation rates during both vegetative and reproductive growth stages emphasize that cultural, nutrient, and water management practices must be coordinated to provide a minimum stress production environment for high corn yield.

Soil‐Dependent Spectral Response in a Developing Plant Canopy1

Abstract: A major problem in the use of remote sensing techniques to assess plant biomass and condition over incomplete canopies concerns the soil background contribution toward measured spectral response. An understanding of this soil signal is essential to better relate canopy spectra with plant properties. An interactive, plant-soil radiant flux model was developed to separate spectral variations associated with soil background from those attributable to vegetation. Field measured spectra taken over n developing cotton (Gossypium hirsutum L.) canopy with four soil types (Cumulic Cryoboroll, Typic Torrifluvent, Ustollic Haplargid, and Typic Calciorthid) alternately inserted underneath were decomposed into soil and vegetation spectra by utilizing the model in a principal component analysis. The soil component included all radiation penetrating the canopy and interacting with the underlying soil. The vegetation component represented all radiation reflected directly from the plant cover with no soil interaction. The soil component was found to resemble the spectral response of green vegetation due to the scattering and transmittance properties of the overlying plant canopy. Results show how the soil signal mixes into various vegetation indices inhibiting reliable vegetation discrimination. The potential improvements in vegetation analysis that can result from filtering soil background response from plant-canopy spectra are also discussed. Additionul index words: Remote sensing, Principal component analysis, Cotton, Gossypium hirsutum L. MAJOR goal in remote sensing research of vegeA tative canopies is the separation of spectral changes due to vegetation response from those attributable to soil background. The problem is especially important in areas where there occurs significant spatial or temporal soil surface variations, or both. In arid and semi-arid environments, complex associations of soil types and sparse vegetation covers often prohibit the extraction of reliable vegetation information (Elvidge and Lyon, 1985; Huete et al., 1984). Imgated agricultural soils undergo numerous temporal wetting and drying cycles and exhibit irregular drying patterns. As a result, spectral responses associated with differences in vegetation-related parameters (leaf area index, biomass, cover, stress, disease) are difficult to detect amidst a variable soil background matrix since canopy response is sensitive to both forms of variation. Numerous spectral vegetation indices have been developed with the aim of minimizing soil background variations while enhancing the vegetation signal. These include near-infrared and red band ratios (Tucker, 1979), the perpendicular vegetation index (Richardson and Wiegand, 1977) and the green vegetation index (Kauth and Thomas, 1976). These indices have been found effective in reducing spectral variations from soils devoid of vegetation. This is accomplished by ratioing soil spectra or utilizing a principal axis of soil spectral variation termed the “soil line” (Richardson and Wiegand, 1977). It is assumed that soil influences are further reduced with the emergence of green vegetation due to canopy closure. Several studies, however, have shown serious limitations in the use of these indices for vegetation assessment and characterization (Jackson et al., 1983; Colwell, 1974; Huete et al., 1985). These studies have shown soil brightness effects whereby darker (or lighter) background substrates resulted in greater vegetation 61 index values over constant vegetation amounts. Huete et al. (1 985) found all the above vegetation indices to be sensitive to soil background even when bare soil spectra were effectively normalized. Furthermore, they found soil influences to be more serious at canopy closures of 50 to 75% green cover than at either lower or higher levels. This suggests that soil and vegetation spectra mix in an interactive manner to produce composite, canopy response. Various models have been developed which describe composite canopy reflectance in terms of the fractional amounts of sunlit and shaded soil and sunlit and shaded vegetation (Jackson et al., 1979). These models assume that the respective components can be modeled as additive, independent features. As with the vegetation indices, these models predict lower soil influences with canopy closure since the fractional content of soil viewed by a sensor decreases. Deterministic plant canopy models such as those by Suits (1972) and Verhoef and Bunnik (1976) are much more complex and require detailed input model parameters. These models show that plant canopies selectively transmit radiant flux over different spectral regions. Chance (1977), using the model of Suits (1972) for a dense wheat cover, found wheat canopy reflectance to be independent of soil background in the visible spectral region and dependent in the near infrared. There is an absence of simple plant canopy models that can adequately describe the manner in which soil and vegetation spectra mix to produce a composite canopy response. It is of interest to determine what the soil contribution is toward measured canopy response and how this soil spectral component influences the various vegetation indices. This is essential to effectively remove soil influences and better relate plant properties to experimental canopy spectra. In this study, a first order interactive model of radiant flux in plant canopies is utilized to separate experimental canopy spectra into soil-dependent and vegetation spectral components. The spectral properties of the isolated components are subsequently used as input for an analysis of soil background influences on vegetation measures. MATERIALS AND METHODS

In situ nuclear magnetic resonance imaging of roots: influence of soil type, ferromagnetic particle content, and soil water

Abstract: protons with a high degree of molecular-level mobility The paucity of root information combined with the difficulty in obtaining it make new approaches imperative. The observation of roots is essential to the understanding of plant growth and productivity. Proton ('H) nuclear magnetic resonance (NMR) imaging offers a noninvasive method for the study of both root morphology and function in situ. Herein, NRIR imaging of plant root systems was evaluated for southeastern U.S. agricultural soil series from 30 different sites, and eight common artificial soil substrates, as a function of soil type, ferromagnetic particle content, and soil water, using a 1.5-tesla medical research NMR imaging system and Vicia faba L. seedlings grown in the soils. Roots of about I mm in diameter and I-mm-diam capillaries of water were undetectable by NMR imaging and conventional NiLIR in soils with ferromagnetic particle contents of greater than about 3%by weight. Below 4%, ferromagnetic particle content did not correlate well with NbIR image quality, but the presence or absence of NMR signals from water-containing capillaries embedded in soil samples in a conventional NNIR experiment reliably reflected soil suitability for NMR root imaging. Images of seedlings in four of the artificial soils (perlite, Ottawa sand, peatlite, and peat) and seven of the native soils (Wynnville fine sandy loam, Lucy loamy sand. Dothan sandy loam, Lakeland sand, Kinston loamy sand, Blanton loamy sand, and Eustis fine sandy loam) showed excellent spatial resolution and accurate reproduction of the root systems when they were extricated from the soils. However, the results from three of the artificial soils (perlite. Ottawa sand. and peat) were significantly compromised by background NMR signals that derived from soil water. In the seven native soils, soil water to near saturation was rendered essentially invisible by the NMR imaging sequence employed, thereby demonstrating escellent root-to-soil image contrast. Several root pathologies apparent in the images were identified. The results reveal that 'HNMR imaging is a practical tool for the nondestructive. noninvasive investigation of plant root systems in many natural agricultural soils at virtually any stage of a water stress

Modeling Long-Term Crop Response to Fertilizer Phosphorus. I. The Model1

Abstract: Prediction of long-term crop response to fertilizer P should result In more efficient use of this resource. To achieve this, a simple model designed to calculate the long-term recovery of fertilizer P was de­ veloped and is presented here. In the model, both a labile and a stable P pool are distinguished. With time intervals of l yr, the model calculates the P transfers between the pools, the uptake of P by the crop, and the resulting pool sizes. Most input data required to operate the model can be obtained from ordinary one-season fertilizer P trials. Input data, model parameters, and initial pools can be derived from field trials, and the model can be used to calculate long-term recovery of fertilizer P. The sensitivity of the model is demonstrated by changing par~meter values. The model can also be used to es­ tablish long-term fertilizer recommendations for a certain target P uptake. Required rates of fertilizer P are calculated for different soils, fertilizer types, target uptakes, and periods of time. Additio1Ull indu words: Fertilizer recommendations, Labile phos­ phorus, Phosphorus uptake, Simulation model, Soil phosphorus cy­

Effect of Soil pH on Crop Yield in Northern Idaho1

Abstract: Etude sur 5 ans. Regroupement des donnees de 39 essais de plein champ concernant le chaulage et l'apport de soufre elementaire permettant d'etablir des modeles mathematiques de l'interaction pH du sol-rendement