Showing papers in "Agronomy Journal in 1971"

Estimating Leaf Water Content by Reflectance Measurements1

Abstract: Regression equations expressing reflectance of incidentlight from the upper (adaxial) surface of single leaves as a function of their relative turgidity and water content were developed. Reflectance at the 1.45- and 1.93-µ water absorption bands was significantly related (p = 0.01) to the leaf relative turgidity or water content. However, because of variations in internal leaf structure associated with the availability of water during leaf development, the ability to predict the leaf water status from reflectance easurements was poor. With cotton (Gossypium hirsutum L.) the greatest change in reflectance occurs when the relative turgidity is below 70% and the leaves are visibly wilted. Within the relative turgidity range, 70 to 80%, reflectance changes are small and may not be definable for predictive purposes because of variation among leaves of field-grown cotton caused by age differences and osmotic stresses.

Reflectance and internal structure of leaves from several crops during a growing season.

Abstract: Measurements of spectral reflectance characteristics during a growing season of leaves from six crops are reported. These crops include soybeans, wheat, oats, sorghum, corn, and sudangrass. The characteristics measured are related to changes in leaf structure and water content.

Growth and Water Potential of Root Crops as Influenced by Salinity and Relative Humidity1

Abstract: The interaction of relative humidity and salinity on garden beet, onion, and radish was studied in sunlit climate chambers at temperatures cycling daily between 26 and 10 C. Average daytime relative humidity (RH) was controlled at 45 and 90%. The root medium of each crop was maintained at four different osmotic potentials, the range depending on the crop's salt tolerance. With a nonsaline root medium, increasing RH from 45 to 90% increased the yield of beet by 50% and radish by 15%, but did not enhance the yield of onion. In saline root media, high RH significantly raised the salinity level at which the yield was reduced to 50% of the nonsaline yield for onion and radish, but did not affect this level for beet. Linear relationships between leaf water (ΨL) and osmotic (πL) potentials and the osmotic potential of the root medium (πS) were found for all three crops. Except low values of πS (high salinity), ΨL and πL were lower at 45% RH than at 90% RH. Leaf turgot potential was not affected by salinity in beet and onion but was reduced in radish. The relationship between crop yield and ΨL was linear. The difference in ΨL for plants between full yield and almost no yield was only 13 bars for beet, 6 bars for radish, and 4 bars for onion.

Corn Yields with Fall, Spring, and Sidedress Nitrogen1

Abstract: Studies in central and northern Illinois at 4 locations and 12 location-years were conducted with 5 rates of N applied in the fall and as spring-preplant. Sidedress N was also included at 1 of the 4 locations for 4 years. Relative efficiency of the times of application was calculated by dividing the corn (Zea mays L.) yield increase from a given rate of N added at one time by the yield increase from the same rate of N applied at another time. At the Carthage and Hartsburg locations the 3-year average relative efficiencies of fall- versus spring-applied N are about 0.8 and 0.9 (fall was 80 and 90% as effective as spring) at N rates of 67 and 134 kg/ha, respectively. Fall and spring N were about equally effective at 201 and 268 kg/ha of N. There was generally little yield response to N rates greater than 201 kg/ha at Carthage and Hartsburg. Fall and spring N gave similar corn yields for all rates of N at Urbana. For the 4-year average at DeKalb, sidedress N was the most effective, spring N was intermediate, and fall-applied N was the least effective. The difference between spring and sidedress N was less than that between fall and spring N. There was considerable year-to-year variation in relative efficiency. The importance of the time at which conditions suitable for N loss occur is discussed.

Water Relations and Growth of Cotton as Influenced by Salinity and Relative Humidity1

Abstract: Soil salinity and atmospheric relative humidity influence plant growth, but few data are available showing the interaction between them. This interaction was studied with cotton (Gossypium hirsutum) in four sunlit climate chambers at temperatures cycling daily between 38 and 26 C. Relative humidity was controlled at 25, 40, 65, and 90%. The root medium was maintained at osmotic potentials of −0.4, −5, −10, and −15 bars. Relative humidity significantly affected shoot growth only in the 90% relative humidity treatment, where growth was increased about 40%. The shoot-to-root ratio at high humidities was at least double the ratio at low humidities. The 50% yield decrement based on leaf area or plant dry weight occurred at an osmotic potential of −5 bars. Because the anthers of the cotton flowers in the 25 and 90% relative humidity treatments did not dehisce, seed cotton yields at these relative humidities were essentially zero. Seed cotton yields per plant at 40 and 65% relative humidities were comparable to or greater than field yields. Transpiration per unit leaf area for the entire experiment increased an average of 80% for all salinity levels as the relative humidity decreased from 90 to 25% and decreased slightly with increasing salinity in all humidity treatments. Transpiration per unit leaf area decreased as the plants matured and tended to approach the same value for all treatments near the end of the experiment. The relative yield of dry matter and leaf area as a function of salinity was the same at all relative humidities, indicating that no interaction between salinity and relative humidity occurred.

A Sunfleck Theory for Plant Canopies I. Lengths of Sunlit Segments along a Transect1

Abstract: The size distribution of sunflecks under a plant canopy can be represented by the length distribution of sunlit segments along a straight-line transect drawn under the canopy. A mathematical connection is deduced between this sunlit-length distribution and the probability, as a function of length, that a short line placed randomly under the canopy will be everywhere in sunlight. In turn, this probability distribution is deduced for randomly-placed leaves, from which the above-mentioned connection yields the desired sunlit-length distribution. In subsequent papers this basic result will be used to predict the effect of penumbra — fuzzy shadow edges caused by the finite angular size of the sun — upon the light intensity distributions within or beneath canopies, as a function of leaf size, shape, height, density, and orientation.

Crop Response to Excessive Zinc Fertilization of Alkaline Soil1

Abstract: The objective of this research was to evaluate the tolerance of economic plant species to excessive levels of available Zn in the soil Fifteen field crop and three vegetable crop species were grown under uniform conditions in a growth chamber in alkaline soil treated with 10, 100, 200, 300, 400, and 500 ppm Zn Response was evaluated in terms of dry matter yield decrease (YD) and Zn concentration in tops Grass species were most sensitive and had maximum YD's greater than 40% Alfalfa (Medicago saliva L), Alaska pea (Pisuni sativum L), tomato (Lycopersicon esculentum Mill), lettuce (Latuca saliva L), spinach (Spinacia oleracea), and sugarbeet (Beta vulgaris L) had YD's between 20 and 40% Field bean (Phaseolus vulgaris L), snap bean, russet potato (Solanum tuberosum L), white potato, clover (Trifolium repens L), and Perfection pea (Pisum sativum L) did not undergo a significant YD Zinc concentrations in tops associated with a 20% YD ranged from 240 ppm for field bean to 740 ppm for sugarbeet, with most crops falling in a 400 to 600-ppm range The most sensitive species tolerated Zn additions of 200 to 300 ppm before undergoing a significant YD Crops that underwent a significant YD because of excess Zn were stunted but showed no discoloration, malformation, or necrosis indicative of a direct metal toxicity

A Method for Determining Aluminum Response of Barley in Nutrient Solution in Comparison to Response in Al-Toxic Soil1

Abstract: A method was developed to screen barley populations for Al response in nutrient cultures. Thirty varieties and selections were grown in tanks of nutrient solutions containing either O or 4 ppm Al at initial pH 4.8. Aluminum tolerance ratings obtained by this method were in good agreement with those obtained previously in pots of acid, Al-toxic soils in the greenhouse and in field plots. In general, Al injury was characterized by an increase in the number of roots and a decrease in root length and root weight per plant. Highly significant (1% level) correlation coefficients were found between root length and weight (r=0.93); root weight and number of roots (r=−0.76); and root length and number of roots (r=−0.83). The correlation coefficient between root weight in solution and in soil (r=0.75) was also significant at the 1% level. The method presented is satisfactory for screening barley varieties for Al tolerance.