Search Results
A 3-year experiment was conducted to determine the optimum fertilizer N requirements of fresh-market tomato (Lycopersicon esculentum Mill.) `Sunbeam' grown on a hairy vetch (Vicia villosa Roth.) or black polyethylene mulch. In 1993 and 1994, four rates of fertilizer N (0, 56, 112, and 168 kg·ha-1) as water-soluble NH4NO3 were applied in 14 equal applications through the trickle irrigation system starting 1 week after planting. Four additional rates (224, 280, 336, and 392 kg·ha-1) were applied in 1995 to assess the plant response to supra-optimal levels of N. Hairy vetch produced 3.3–4.5 t·ha-1 of above-ground biomass and a total N content of 126–169 kg·ha-1 in the above-ground biomass. Leaf N content at 7 weeks after transplanting of tomatoes correlated positively with yield from black polyethylene but did not correlate with yield from the hairy vetch plots where leaf N content was optimal at all N rates. Predicted tomato yields were higher for the hairy vetch than for the black polyethylene treatment at all applied N rates in all years. Tomatoes grown in black polyethylene required N at 130 to 144 kg·ha-1 to achieve yields equivalent to those grown following unfertilized hairy vetch. Tomato yield increased in response to applied N in both mulches in all 3 years; optimum N rates of 89 and 190 kg·ha-1 in hairy vetch and black polyethylene, respectively, were predicted by a linear plateau model, and 124 and 295 kg·ha-1 by a quadratic plateau model. The linear plateau model is recommended because it would allow less N to become available for runoff and leaching.
Abstract
Seedlings of highbush blueberry (Vaccinium corymbosum L.) subjected to 3 fungal treatments and 2 soil pH levels (4.2 and limed to 6.0) displayed no significant treatment interaction in respect to growth, mycorrhizal infection intensity, or nutrient uptake. Among the fungal treatments, there were differences in nutrient uptake and infection intensity, but no difference in total linear stem growth or number of shoots. Lower soil pH resulted in significantly greater stem growth and number of shoots; however, intensity of infection was not significantly different compared to the high pH soil.
Abstract
‘Jersey’ blueberry plants were greenhouse-grown through 1 season with treatments consisting of a factorial combination of 4 soil factors: inoculation with a mycorrhiza-forming fungus; high or low nutrient regime; with or without leachate from a native blueberry soil; and soil porosities corresponding to a clayey, silty, or sandy, and a native blueberry soil, Berryland, as a standard comparison. Although very low in nutrient elements, Berryland soil or its leachate significantly increased plant growth. There was no significant effect on growth from mycorrhizal inoculation at either high or low nutrient levels and only a slight effect from varying the soil free-pore space.
Abstract
The growth and elemental composition of a range of blueberry (Vaccinium sp.) progenies was greenhousetested on 5 unmulched soils. Three of the soils, low in pH and fertility, represented the physiographic regions of the eastern United States; Coastal Plain, Piedmont, and Appalachian Highlands; also included were a high-pH, high-fertility Piedmont soil and a commercial blueberry Coastal Plain soil. Two studies, 10 and 20 weeks in duration, were made with seedlings of crosses of blueberry clones of hybrid origin. Growth was significantly higher for seedlings grown on the commercial blueberry soil in both studies. V. ashei (rabbiteye) seedlings grew significantly larger than all others when measured over all soil types in one experiment but not the other. There were no significant differences in growth among the 4 progenies when averaged over all soil types. Percent sand was positively correlated with growth while both percent silt and clay were negatively correlated with growth. Plant composition was generally within acceptable levels for Ca, Mg, K, Fe, and Zn. Plant Mn and Al, although variable, tended to be higher than reported values. Soil Mn was significantly and negatively correlated with growth. It was possible to select individual seedlings which grew well on each of the mineral soils represented in the study.
Abstract
The effect of polyethylene glycol (PEG)-induced water stress on stomatal and nonstomatal inhibition of photosynthesis of apple seedlings (Malus domestica Borkh.) grown in solution culture was investigated. Water stress was applied gradually by modifying the nutrient solution water potential daily to a minimum of -8.0 bar. Nutrient solution of less than or equal to water potentials -6 bar decreased net and gross photosynthesis rates. Stomatal and nonstomatal factors were responsible for photosynthetic inhibition. Nonstomatal inhibition of photosynthesis appears to be due to decreased capacity for CO2 fixation and not increased photorespiration. The ratio of gross to net photosynthesis was not affected. A higher level of water stress was required to affect mesophyll resistance than stomatal resistance and/or there was a lag time for mesophyll resistance to respond to stress.
Abstract
Apple seedlings (Malus domestica Borkh.) were grown in the greenhouse under a range of polyethylene glycol (PEG)-induced osmotic potential stresses up to −7.5 bars. Water use by seedlings (ml water consumed/dm2 leaf area) responded to ambient temperature fluctuations after 4 days in the solution. During the first 4 days after initiation of the stress, no response was obtained indicating that the seedlings were undergoing an “adaptation period.” Plants receiving higher osmotic stresses were less able to respond to ambient temperature fluctuations as measured by transpiration. Transpiration rate decreased as osmotic stress was increased. PEG-induced osmotic water stress and water stress in soil were compared, the latter by letting the soil mass dry out. Comparable transpiration rates from the 2 methods, when plotted, showed that PEG-induced osmotic stresses of −0.5 and −4.0 bar were equivalent to greenhouse potting soil at 75% of field capacity and approaching the wilting point, respectively. It was concluded that the PEG-induced water stress was similar to water stress in soil, thus PEG-induced stress can be used in experiments with apples to study various effects of water stress. Use of a freezing point depression osmometer in determining solution osmotic potentials of PEG-modified solutions is described.
Abstract
Polyethylene glycol (PEG)-induced water stress in nutrient solutions decreased both water consumption and 45Ca uptake by apple seedlings (Malus domestica Borkh.) The decrease in water uptake was more severe than the decrease in 45Ca uptake. When 45Ca uptake was calculated on the basis of water consumption, it was found that 45Ca uptake was not dependent on water uptake although water was necessary for movement of 45Ca. In split-root experiments, PEG and 45Ca were either applied to the same half of the root or to separate halves. Calcium uptake decreased in plants subjected to water stress. The results indicated that the site of this decrease was at the root, not the aerial portion of the plant which, indirectly, may affect root function and thus 45Ca uptake. Split-root experiments also indicated that the unstressed half of the root cannot fully compensate for the stressed half of the root in either water or 45Ca uptake. Water use of plants with half of their root under a −5.0 bar water stress was decreased by 30%. Urea-nitrogen pretreatment did not modify the effect of osmotic stress on leaf Ca, Mg and K concentrations, water use or dry matter production during the period of applied water stress. All these parameters decreased with increasing solution osmotic stress.
Abstract
A near-infrared reflectance (NIR) technique was developed that provides a rapid, nondestructive, nonchemical analysis of ground apple (Malus domestica Borkh.) leaf tissue for predicting total N content. Leaf tissue samples of apple with known (chemical) leaf N concentrations ranging from about 1.6% to 2.9% N were used in the calibration of the NIR technique. The NIR technique was highly correlated (r = 0.923) with the chemically determined total leaf N content. Prediction of tissue N values was performed with a standard error of estimate of about ±0.10% N. This value compares favorably with the standard error obtained for duplicate determinations preformed by a tissue analysis facility employing standard chemical (Kjeldahl) digestion methodology.