Richard Y. Evans

Rapid direct determination of ammonium and nitrate in soil and plant tissue extracts

Abstract The diffusion‐conductivity method (DCM) for NH4 + and NO3 ‐determinations in soil and plant tissue extracts is tolerant of sample color and turbidity. The instrument can be calibrated for direct analysis of extracts from either low or high level samples. Extracts can be processed at one per minute. Ammonium and NO3 ‐ can be determined simultaneously at this rate with a two channel prototype instrument. The use of serum filters simplifies sample extract preparation and avoids the NH4 + and NO3 ‐ contamination problem that has been documented for filter papers. The instrument sample intake tube can aspirate extracts directly from the serum filter tube. A variety of soil or plant extracting solutions can be used for both NH4 + and NO3 ‐ determinations. Interference in NO3 ‐determinations has been encountered in a few samples where it appears to be due to a high phenolic content. For these samples, interference is minimized by using two NO3 ‐ reduction cartridges in series. Comparisons of the DCM pro...

Cyclic nitrogen uptake by greenhouse roses

Abstract A recirculating nutrient solution system was constructed to study N uptake by greenhouse ‘Royalty’ rose plants in relation to irradiance and the developmental stage of the crop. The rate of N uptake followed a cyclical pattern that was related to shoot development and harvest, but independent of transpiration rate. The N uptake rate changed four- to five-fold during a single cycle of flower shoot growth (e.g. 29–146 mg N per plant day −1 ). Following a flower harvest, the N uptake rate decreased even as the new flower shoots began to develop. The lowest N uptake occurred when the shoot elongation rate was at its maximum. Thereafter, uptake rates increased, with the highest rate occurring as the flower shoots reached commercial maturity. Potassium, Ca, Mg and P followed the same pattern of uptake observed for N. Irradiance did not control the periodicity of the N uptake cycles but did affect the average daily plant N demand. Uptake rates in summer days (approximately 60–70 mg N per plant day −1 ) were about twice of those in winter (approximately 30 mg N per plant day −1 ). The total annual plant N uptake (16.8 g N per plant year −1 ) was in close agreement with the yearly plant N demand calculated for container-grown roses.

Leaching losses of N from container-grown roses

Abstract ‘Royalty’ roses were grown under different leaching rates and applied N concentrations for 1 year in 20-1 microlysimeters in a greenhouse. During this period, there were eight synchronized flowering flushes at approximately 6-week intervals. Analysis of leachates collected from the microlysimeters indicated leaching losses of 21, 40 and 49% of the applied N from plants irrigated at a leaching fraction of 25% with nutrient solutions containing 77, 154 and 231 ppm N, respectively. Average leachate N concentrations were 79, 257 and 441 ppm. There were no significant differences among treatments in number of flowers or harvested dry matter per plant, and, except for the 77 ppm N treatment, only minor differences in leaf N content (3.2–3.4%). The concentration of the 77 ppm N treatment was increased to 105 ppm in April because of the appearance of N deficiency symptoms. The N present in the harvested flowers accounted for 49, 24 and 21% of the N applied to the 77 (105), 154 and 231 ppm N treatments. Plants irrigated with 154 ppm N at leaching fractions of 10, 25 and 50% had corresponding N leaching losses of 22, 38 and 56%. The average leachate N concentrations were 296, 240 and 181 ppm, respectively. The 50% leaching fraction produced yields that were significantly higher than those of the other treatments. The leaf N content was similar among the treatments (3.3–3.4%), but the N recovered in the harvested flowers accounted for 34, 30 and 22% of that applied to the 10, 25 and 50% leaching fraction treatments. The plant N demand estimated from these studies would be met by the addition of N fertilizer at levels substantially lower than those currently recommended.

Nitrogen partitioning in rose plants over a flowering cycle

Abstract Nitrogen uptake by greenhouse roses is out of phase with flower shoot elongation, such that N uptake is lowest when shoots are elongating rapidly and highest when flower shoots have ceased elongation. Fertilizer labeled with 15 N was supplied at different stages of one flowering cycle to hydroponically grown ‘Royalty’ rose plants to study the partitioning of recently absorbed N and the dynamics of total N within the plant. After a 2 day exposure, whole plants were harvested, separated into old and new leaves, stems, and roots, then analyzed for total N and 15 N enrichment. During the period of rapid shoot elongation, N uptake from the nutrient solution supplied 16–36% of flower shoot N. The remainder, representing most of the N in the growing shoots, came from N stored in other organs, particularly old stems and leaves. The increased N uptake that occurred later in the flowering cycle was sufficient to meet flower shoot N demand and to replenish the N supply in the old foliage and woody tissues. Those organs continued to accumulate N until the subsequent bud break, when it became available for the next cycle of flower shoot development.

Enhancement of short-term nitrogen uptake by greenhouse roses under intermittent N-deprivation

A recirculating nutrient solution system was utilized to study the effect of intermittent N deprivation on N uptake by mature ‘Royalty’ rose over the course of one flowering cycle.Plants received a nutrient solution lacking N for 4, 8 or 16 days, after which one containing NO3−N (0.75 mM) was supplied for 4 days. N-deprivation resulted in a 2–3 fold increase in N uptake rate compared to control plants supplied continuously with N. The magnitude of this deprivation-enhanced N uptake was not affected by either the duration of N-deprivation or the plant developmental stage. Over the course of the flowering cycle, the total cumulative N uptake by the plants was 95, 66, and 44% of the control plants in the 4, 8 and 16-day deprivation treatments, respectively. A characteristic diurnal pattern of N uptake occurred in both N-starved and control plants. Uptake oscillated between minimum rates in the morning and maximum rates in the evening, the latter occurring 4–6 hr after the maximum rate of transpiration.

Wireless Sensor Network for Precision Irrigation Control in Horticultural Crops

Wireless sensor networks for crop monitoring have become more common, but typically support sensing only and not control. Much of the work on wireless sensor networks with integrated control has been conducted in academic research. To promote the accessibility of commercially-available wireless sensing and control networks, valve control hardware and software were developed to be compatible with a commercial wireless sensor node. The work was conducted in collaboration with a wireless network vendor such that the research conducted with this wireless system and the product itself would be available to growers. The valve actuation system included custom node firmware, actuator hardware and firmware, and base computer communication software and a web interface. Network range, energy consumption, and actuator operation were characterized. A commercial soil moisture sensor was selected to monitor nursery container water content for closed-loop irrigation control in container nurseries.

Nitrogen Critical Level Determination in The Woody Ornamental Shrub Euonymus fortunei

ABSTRACT We determined the critical nitrogen (N) level on greenhouse-grown winter creeper (Euonymus fortunei Hand. Mazz. ‘Colorata’) in one-gallon containers by adding N in doses of 0 to 400 mg/pot as ammonium nitrate (NH4NO3) and growing plants for 50 days without leaching. At harvest, leaf N concentrations were similar in all treatments up to 150 mg/pot, but increased with applied N above 150 mg/pot. Yield increased with increasing leaf N up to about 1% N, but was relatively constant at higher leaf N. The leaf N critical level was 1.03%. Shoot:root ratio, based on new growth, decreased with applied N. This method for critical level determination provides an accurate description of the relationship between leaf N and growth and may be used by growers to improve fertilizer use efficiency.

Respiration of geranium and petunia in response to low night temperature

Abstract The morphology and rate of development of some bedding plant species is altered by growth at low night temperatures. This cultural practice is of interest because it results in lower greenhouse energy costs and higher productivity at low photosynthetic photon flux. Low night temperatures and changes in the carbohydrate content of the plants may alter energy losses from maintenance respiration. To test this hypothesis, seedlings of geranium (cultivar ‘Red Elite’) and petunia (cultivar ‘Snow Cloud’) were grown at day temperatures of 25°C and night temperatures of either 7°C or 15.5°C. Thereafter, CO2 evolution in the dark at 21°C was measured and starch, soluble sugar and total nitrogen levels were determined. The respiration rates at 21°C of plants grown at 7°C night temperature were consistently higher than those of plants grown at 15.5°C night temperature. Plants grown at the low night temperature had higher starch and soluble sugar levels, even after 112 h in darkness. Effects of night temperature in winter on maintenance respiration and reserve carbohydrate accumulation are discussed.