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Thomas, Judith F.; Raper, C. David; Weeks, Willard W.
doi: 10.2134/agronj1981.00021962007300040003xpmid: N/A
By altering the timing of reproductive events, temperatures may affect allocation of N and C within soybean [Glycine max (L.) Merrill]. The objective of this study was to determine the changes in partitioning associated with early development of the reproductive sinks. Plants of the determinate cultivar ‘Ransom’ growing in controlled environments were transferred to inductive shortday photoperiods at the V3 stage and grown under 25 combinations of day/night temperatures over a range of day temperatures of 14 to 30 C and night temperatures of 10 to 26 C. Plants from each combination were sampled at 0, 20, 30, and 50 days after the first inductive photoperiod. Plants were separated into leaves, stems, and pods, freeze‐dried, and analyzed for total N and soluble carbohydrates.
doi: 10.2134/agronj1981.00021962007300040004xpmid: N/A
Relatively little information exists on the N and P needs of sunflower (Helianthus annuus L.) on infertile soils in non‐traditional production areas. The effects of four levels each of N (0 to 180 kg/ha) and P (0 to 60 kg/ha) applied to a thermic Typic Rhodustult were evaluated over three seasons. In all seasons there were highly significant seed yield responses to N and P a plied. The nature of the N ✕ P interactions indicated a greater response to N fertilization where P had been applied than in the absence of P fertilization. Maximum seed yields of up to 2,600 kg/ha were four to 13 fold higher than yields in the absence of applied N and P. Protein level in the seed was increased by N but decreased by P fertilization, the opposite effects being generally observed with respect to the oil. Nitrogen and P fertilization markedly increased the protein and oil yields, the N ✕ P interactions indicating that P fertilization was necessary for maximum response to applied N. The ratio of seed N to fertilizer N decreased with increased N fertilization but increased with increased P applied. The food energy yield and energy production efficiency of sunflower increased markedly with both N and P fertilization.
doi: 10.2134/agronj1981.00021962007300040005xpmid: N/A
Identification of Al tolerant sorghum [Sorghum bicolor (L.) Moench] is important if this crop is to be grown successfully on acid, Al‐toxic soils. A rapid method for screening genotypes for Al tolerance was developed by growing over 100 plants in the same container of relatively small volume (50 ml/plant). Mineral element conditions that gave good differential responses for Al tolerance were 148 µmol liter−1 Al, 64 µmol liter−1 P, 7.4 mmol liter−1 Ca, 1.6 mmol liter−1 Mg, 3.9 mmol liter−1 K, 24.7 mmol liter−1 N (8 NO3−:1 NH4+), light (17 hours)/dark (7 hours) temperatures of 28/23 C, and solution pH values below 4.0. Mineral element levels or temperatures higher or lower than these resulted in poorer differential responses of genotypes to Al, either because Al had essentially no effect or Al effects were too severe. Nitrate as a single N source could not be used to screen for Al tolerance because the solution pH increased as plants grew and Al in solution was inactivated. A mixture of NO3− or NH4+ gave better genotypic separation than NO3− or NH4+ alone. Visual Al toxicity symptoms on roots were noted within 10 days, and seminal root lengths could be used to assess Al tolerance of sorghum genotypes. Differences in root and top dry matter yields did not distinguish sorghum genotypes for Al tolerance.
doi: 10.2134/agronj1981.00021962007300040006xpmid: N/A
Quantitative information relating the effects of delayed emergence caused by soil crusting to cotton (Gossypium hirsutum L.) seedling vigor are needed to improve the technology for stand establishment. A greenhouse study measured the effect of crusted soil (Amarillo fine sandy loam, Aridic Paleustalfs) in delaying emergence for 50, 100, and 150% of normal emergence time for constant soil temperatures of 20, 25, and 30 C. Measurements of maximum emergence, seedling survival, hypocotyl diameter, and root disease rating were used as indicators of seedling vigor. Regression analysis indicated that seedling survival and hypocotyl diameter were minimal at 26 and 24 C, respectively, and root disease rating had a maximum value at 24 C. Seedling emergence and survival were significantly reduced when emergence was delayed between 50 and 100% of the normal emergence period, but almost all increase in hypocotyl diameter occurred in the first 50% delay. Estimates of reductions in vigor for seedlings emerging through crusted soil should be possible by measuring the degree of emergence delay and/ or hypocotyl diameter
Smith, C. Wayne; Varvil, J. J.
doi: 10.2134/agronj1981.00021962007300040007xpmid: N/A
Many areas of the so‐called cotton belt frequently receive hail sufficient to cause measurable damage to cotton (Gossypium hirsutum L.). The indeterminant growth habit of cotton allows for varying degrees of recoverability from hail damage depending upon the stage of growth of the plants when damaged and the severity of damage.
doi: 10.2134/agronj1981.00021962007300040008xpmid: N/A
Perennial grasses can be grown in subtropical areas of the world having little frost damage, but, in many areas low temperatures (1 to 10 C) at higher elevations and lack of moisture may restrict growth of most subtropical forages and create critical feed shortages for livestock. A study of the seasonal distribution of forage production of subtropical grasses was conducted to determine production and quality and to develop improved management practices. Sixteen grasses (four Cynodons, three Paspalums, eight Digitarias, and one Brachiaria) were grown with and without irrigation and harvested at two stubble heights (5 and 10 cm) at 30‐day intervals for 30 consecutive months (March 1973 through August 1975). The experiment was conducted at the Immokalee Research Center in south Florida on a sandy siliceous, hyperthermic, Arenic Haplaquod (Immokalee fine sand) soil. Winter forage production (October through March) was highest for Cynodon spp (27% of total annual yield) and lowest for Paspalum spp. (14% of total annual yield). Plants cut at a 5‐cm stubble initially outyielded plants harvested at 10 cm. However, after 2.5 years little difference was observed in dry matter yield between stubble heights, except for the Paspalum spp. and Brachiaria sp. which continued to produce more forage at the 5‐cm stubble height. Little difference was observed in percentage crude protein and IVOMD between grass entries harvested during the summer growth period with the exception of Brachiaria which was significantly higher in IVOMD. Both crude protein and IVOMD were much lower in forage harvested during the summer than the winter for all grasses, again with the exception of the IVOMD for Brachiaria which had a summer‐winter range of 58 to 64%. This entry was one of the highest in dry matter yield, crude protein, and IVOMD percentage, but produced 83% of its dry matter during the summer. Irrigation had little effect on dry matter production at any season. Higher IVOMD was obtained from cut short with no irrigation. These data indicated that Cynodons harvested at a 5‐cm stubble produced highest dry matter production during the cool winter season, containing high crude protein and IVOMD levels. Dry matter yields in summer were 200 to 300% higher than in winter, however, forage quality was much lower during the summer.
Fales, S. L.; Wakefield, R. C.
doi: 10.2134/agronj1981.00021962007300040009xpmid: N/A
Suppression of woody plants by grasses has been widely reported; but few studies have investigated the factors responsible for the reduced growth and poor appearance often shown by ornamental trees and shrubs planted in association with turfgrass. This research was undertaken to determine the major factors responsible for this phenomenon.
Wolfson, Jane L.; Shearer, Georgia
doi: 10.2134/agronj1981.00021962007300040010xpmid: N/A
Increases in the price of agricultural chemicals and uncertain supplies are likely to cause a reduction of pesticide and fertilizer use in the future. Therefore, it is of interest to compare yields and quality of crops grown under present conventional practice with those grown at the lower limit of chemical intensiveness. In this paper, we report measurements of the amino acid composition of protein from maize (Zea mays L.) grain raised on 14 pairs of fields which did (conventional) and which did not (organic) receive pesticides and standard commercial fertilizers. The pairs of fields were matched for location, cultivar, planting date, and soil type.
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