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  • Author or Editor: F. D. Moore III x
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Abstract

Water and nitrogen loss from field soil cropped to head lettuce with furrow irrigation was measured during three seasons in a semi-arid region. Water applications were reduced during the latter ⅓ of the growth period in an attempt to conserve N and water in the root zone.

Approximately 5 acre feet of water was applied to grow the crop. One-fifth of the applied water drained off and one-half percolated below the root zone. Eighty-nine lb./acre of NO3-N was leached. Two-thirds of the water and three-fourths of the N (soil and applied) which were lost below the root zone were lost during germination. Reducing the total volume of water applied by 1½ acre feet did not reduce water or N loss appreciably and had a deleterious effect on the crop.

Very little N was lost as a result of runoff, but much was moved to the bed tops after the first irrigation. Implications of these findings are discussed.

Open Access

An index “internal slope” derived from the cumulative frequency distribution of individual seed leachate conductivities is related to seed quality; the larger the index value the less variation among individual seeds in a sample (100 seeds) and the higher the seed quality. We have recently developed data acquisition/instrurment control/data smoothing/data analysis software which accesses frequency and cumulative frequency distributions of individual seed conductivities and the derived index on an almost continuous basis from the start of the first soaking.

At present, lack of convergence with regard to curve fitting may occur necessitating multiple sampling times. A “window in time” approach is described whereby index estimates during a two-hour interval within the index stability phase are averaged. Evidence of the method's ability to assess seed vigor will be presented.

Free access

Duration of growth is dependent on morphological events or changes in growth rate. It is the latter that is associated with phasic development. The most productive phase of plant growth is the linear or constant rate phase, primarily because it endures longer than the exponential phase. The purpose of our research was to objectively determine the true tree-height growth pattern, the linear and stationary phases of height growth, and to mathematically derive the maximum slope (maximum growth rate) of the growth curve, its location (inflection point), and the maximum slope of the logarithmic form (maximum relative growth rate) of the growth curve. The data were composed of 333 tree-height records covering 240 years from 200 beechwoods in the U.K. Height-age data were fitted using a splined function (S) and the Chapman-Richards function (CR). The growth curve and critical points on the curve were derived from the CR model. The linear phase began when trees were 9 and lasted 43 years. However, the stationary phase did not begin until age 162. Anecdotal evidence suggests that very little fruiting occurs before age 50. Based on derived critical points and anticipated source-sink dynamics, the reproductive stage should have taken place during the progressive “deceleration phase” when trees were between 31 (location of the maximum slope, also inflection point) and 162 (from quadratic root). The linear phase ended at 52 years, (coinciding with minimum acceleration) and may prove a more accurate estimate than 31. Maximum slope was 1.2 m per year occurring at age 31. Maximum slope of the log curve was 0.14 m·m–1 per year. The advantage of the CR function and the importance of the derived quantities and growth phases will be discussed.

Free access

Carbon dioxide concentrations measured within and above a strawberry plant (Fragaria × ananassa) canopy were significantly higher during enrichment with carbonated water or 900 kg CO2 ha-1 hr-1 applied as gas. Both sources were applied to the base of the plants through drip irrigation tubing under a black polyethylene mulch (0.025 mm) covering or over bare unmulched soil. Mulch affected the concentrations at the top of the strawberry canopy differently for the two sources of CO2 enrichment. Carbonated water was found to reduce the pH of the calcareous soil at the research site (pH 8.2) during and between irrigations. The greatest single pH reduction was 2.6 pH units during irrigation measured in mulched soil; significant soil pH reductions were detected as long as 28 days after irrigation underneath the mulch. Soil pH “duration” below pH 7.4 was 70% greater considering mulch and carbonated water vs. no mulch and carbonated water irrigation.

Free access

Abstract

Potato tubers of Solanum tuberosum cv. Kennebec, produced at elevations from 1533 to 3198 m at 2 levels of insolation per site were grown in a greenhouse at 1533 m to determine the effect of the parental clone's environment on the performance of the succeeding generation. Rate of emergence, early vegetative growth, and tuber growth increased with increasing elevation of the parental clone but there was no significant difference in vegetative growth or tuber yield at vine senescence. The environment of the parental clone had no direct influence on the photosynthetic activity of the clonal progeny, but an inverse relationship between bulking efficiency and altitude of seed tuber production was evident. Shading of the parental clone at each elevation had little influence on the succeeding generation.

Open Access

Multiple electroconductivity readings (μAmps) of leachates from individual seeds during the first 6 hr of imbibition was examined as a possible predictor of seed quality. Readings from each sample of 100 seeds were formed into frequency distributions and the mean, median. and internal slope were calculated using an automated computer retrieval system. Internal slope is a non-central tendency measure based on the slope of a line tangent to the inflection point of the S-shaped cumulative frequency distribution (CFD) of μAmps. Radicle lengths (3 days) and germination (7 days) percentages were regressed on each of the two measures of central tendency and also the CFD shape indicator, internal slope. None of the three predictors were satisfactory for estimating seed vigor (root lengths) of maize (Zea mays L.) or wheat (Triticum aestivum L.) or germination of wheat seed lots. Internal slope was useful in estimating viability of artificially aged maize seeds (r2= 0.91), which compared favorably with our previous results using naturally aged red clover (Trifolium pratense L.) seed lots. Overall the seed quality of the unaged wheat lots was fairly high and the electrolyte leakage test was not sensitive enough to detect differences within these lots.

Free access

Abstract

Performance of raw seeds of 2 lettuce, Lactuca sativa L., cultivars was compared with that of seeds from the same lots that had received 7 different seed coatings. Total emergence and coefficient of variability Of plant weights at 20 days were equal for coated and raw seeds in most instances. Coated seeds emerged 1 to 2 days later than raw seed and resulted in lower seedling weights. Seed coatings make possible precision planting of lettuce with apparently no sacrifice in overall performance.

Open Access

Five seed-quality indices based on individual seed electrolyte leakage tests were evaluated. Zea mays L. seeds were soaked for 6 hours, and individual seed leachate conductivity values were obtained. A total of 100 cells were scanned, one seed per cell, at 5-minute intervals for the first 30 minutes, followed by 15-minute intervals for the remaining 330 minutes. Seeds were allowed to dry for 5 to 7 days at room temperature and then were tested for germinability at 25C for 7 days. Radicle lengths were measured after 72 hours. The Richards function was fitted to cumulative frequency distributions of μAmps to obtain internal slope (IS), mean μAmp, and median μAmp values for each scan. Initial leach rate (ILR) was estimated after fitting hyperbolic functions to μAmp vs. soak time data. Average leach rate (ALR) was also derived from fitting the Richards function to μAmp vs. soak time data. Linear regression of seed quality on IS, mean, and median μAmp values after 5 hours of imbibition yielded r2 values of 0.91, 0.81, and 0.86 for predicting viability and 0.56, 0.46, 0.52 for predicting radicle length. Thus, IS was the best seed quality predictor, followed closely by median and mean μAmp values. ILR and ALR were not correlated with seed quality.

Free access

Seed hydration and dehydration affects many physiological reactions, including priming, accelerated aging, and desiccation intolerance. Maize grains were repeatedly imbibed and desiccated, or imbibed and held for periods of time to identify the role of each of these factors. Grains were equilibrated to 12% moisture content (mc) and subjected to cycles (up to 14) of hydration (2 hours) and immediate dryback, or one hydration of 2 to 12 hours and dryback. Germination and vigor (root length and leachate conductivity) were determined after each cycle. Grains adjusted to three levels of hydration (27%, 34%, and 40%) were held for up to 10 days in a sealed desiccator. Each day samples were taken and either dried to the original mc prior to evaluation, or evaluated immediately as above. With each cycle of 2 hours of imbibition, seed mc increased (22% to 39%). Root lengths increased (priming effect) during the early cycles of imbibition and dryback. Decline in germination after eight cycles was a result of either accelerated aging or desiccation intolerance. Based on the results of the holding study, both factors contributed to deterioration, but desiccation intolerance was only observed when mc was above 27%. Conductivity of grain leachates was not correlated with loss of germination or vigor in whole grains, but appeared to reflect deterioration in isolated embryos.

Free access