rates are critical for meeting plant needs and improving nitrogen utilization efficiency ( Zhang et al., 2008 ). Limaux et al. (1999) reported that the timing of fertilizer N applications has a significant effect on the uptake of fertilizer N and the
chemistry, medicine, and agriculture research and is often used to study the movement of N in plants ( Lajtha and Michener, 1994 ). Using a stable isotope as a tracer, the uptake of N and its absorption efficiency can be determined more accurately compared
Abstract
Urea frequently is applied to turfs in liquid formulation at low water application rates which enhance potential foliar N uptake. This study was conducted to evaluate foliar N uptake by several cool-season turfgrasses treated with urea applied at low water volume (35 ml · m−2). Urea was applied foliarly to 8 turfgrasses at 2.5 g N m−2 in 35 ml m−2 of water. Verdure was harvested prior to treatment and after treatment at 24, 48, and 72 hr. Total N-uptake increases were primarily a response to increased the percentage of N, since dry matter production was stable for each turfgrass throughout the 72 hr. Maximum N-uptake occurred 24 hr after treatment. Any significant decrease in N-uptake over time suggested N-movement out of the sampling zone. Turfgrass species and cultivars showed differences in total N-uptake which resulted from initial variations in dry matter, percentage of tissue N, and variations in N-uptake rate. The percentage of N recoveries ranged from 31% to 61% for ‘Park’ Kentucky bluegrass and ‘Highlight’ chewings fescue, respectively. Cultivar differences indicated that ‘Baron’ Kentucky bluegrass was more efficient in relation to foliar N-uptake than ‘Park’ Kentucky bluegrass.
As a result of long-term application, some fungicides may accumulate in the soil to levels that can affect soil N transformations and plant growth. Studies were initiated to compare benomyl, captan, and lime-sulfur fungicides with the biological nitrification inhibitors (NI) nitrapyrin and terrazole for their effects on biological nitrification and denitrification, and tomato (Lycopersicon esculentum Mill.) growth and N uptake. In laboratory studies, inhibition of nitrification was less than 5% in a Tifton l.s. soil incubated with 10 μg g -1 a.i. of benomyl but was about 51%, 72%, and more than 85% when amended with lime-sulfur, captan, and NI, respectively. Similarly, increased inhibitory effects on denitrification of NO3 were obtained in a liquid media incubated anaerobically with either NI (37%) than captan or lime-sulfur (25%) while benomyl had no significant effect. In greenhouse studies with tomato plants, weekly drench applications of 0.25 μg a.i. g -1 soil of the appropriate chemical for 4 weeks with three NH4:NO3 ratios showed that the NI and captan produced the greatest plant biomass and N uptake, but benomyl and lime-sulfur had no main effect while all fungicides interacted with the N ratio to affect plant growth and N uptake.
N deprivation is known to increase the rate of N uptake by graminaceous plants, but such response has not been reported for mature woody plants. A recirculating nutrient solution system was utilized to study the effect of intermittent N-deprivation on N uptake by mature `Royalty' rose plants. Plants received a nutrient solution lacking N for 4, 8 or 16 days, after which one containing N 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 (e.g., 143 vs 62 mg N plant-1 day-t). The magnitude of this deprivation-enhanced N uptake was not affected by either the duration of N-deprivation or the plant developmental stage.
A characteristic diurnal pattern of N uptake was observed 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 transpiration rates.
The ability to increase the rate of N uptake in roses by depriving them of N for several days may be of practical importance for increasing N fertilizer use efficiency and decreasing N losses to leaching.
Strawberries (Fragaria xananassa Duch. .Osogrande.) were grown hydroponically with three NO3-N concentrations (3.75, 7.5, or 15.0 mM) to determine effects of varying concentration on NO3-N uptake and reduction rates, and to relate these processes to growth and fruit yield. Plants were grown for 32 weeks, and NO3-N uptake and nitrate reductase (NR) activities in roots and shoots were measured during vegetative and reproductive growth. In general, NO3-N uptake rates increased as NO3-N concentration in the hydroponics system increased. Tissue NO3-. concentration also increased as external NO3-N concentration increased, reflecting the differences in uptake rates. There was no effect of external NO3-N concentration on NR activities in leaves or roots during either stage of development. Leaf NR activity averaged ~360 nmol NO2 formed/g fresh weight (FW)/h over both developmental stages, while NR activity in roots was much lower, averaging ~115 nmol NO2 formed/g FW/h. Vegetative organ FW, dry weight (DW), and total fruit yield were unaffected by NO3-N concentration. These data suggest that the inability of strawberry to increase growth and fruit yield in response to increasing NO3-N concentrations is not due to limitations in NO3-N uptake rates, but rather to limitations in NO3 - reduction and/or assimilation in both roots and leaves.
Abstract
In a 3-year study sulfur-coated urea (SCU) resulted in differences in crop response which were related to the different N release rates. On Decatur silty clay loam at Normal, Alabama, SCU with relatively high N-dissolution rates performed best in terms of yield and N uptake for turnip greens, Brassica campestris L. (Rapifera group) while SCU with a slower dissolution rate performed better on Morrison sandy loam at Tuskegee, Alabama. On cabbage, Brassica oleracea L. (Capitata group) SCUs performed similar to ammonium nitrate (AN) and uncoated urea (UCU). With tomato, Lycopersicon esculetum Mill., spring-applied SCU with the highest dissolution rate, performed as well as split applications of AN, indicating the possibility for labor saving with SCU through reduced number of applications. Effect of SCU on nitrate accumulation was minimal. At harvest in the top 15 cm soil the total N content was highest in tomato plots treated with split AN, followed by SCU-A, SCU-C, and AN, respectively.
Microsprinkler irrigation may result in increased efficiency of N and water application to citrus. However, best management practices (BMPs) have not yet been developed for microsprinkler use, particularly on newly established citrus. Experiments were conducted during 1997-98 in central Arizona to evaluate the effects of N rate and fertigation frequency on `Newhall' navel oranges (Citrus sinensis) planted in Mar. 1997. Two experiments were conducted, each with factorial combinations of N rate (0 to 204 g/tree/year) and fertigation frequency (weekly to three times per year). In one experiment, nonlabeled N fertilizer was used, and in the other 15N-labeled fertilizer was used. Trunk diameter, leaf N, and 15N partitioning in the trees were monitored. During 1997, neither trunk diameter nor leaf N were affected by N rate or fertigation frequency. No more than 6% of N applied was found in the trees. During 1998, leaf N in fertilized plots was significantly higher than in nonfertilized plots, but leaf N in all trees remained above the critical N concentration of 25 mg·g-1. During 1998, no more than 25% of the fertilizer N applied was taken up by the trees. Results suggest that N applications are not needed during the first growing season after planting for microsprinkler-irrigated citrus in Arizona. Only low rates of N (≤68 g/tree/yr) may be needed during the second growing season to maintain adequate tree N reserves.
Abstract
Plant dry weight of tomato (Lycopersicon esculentum Mill.) grown in aged bark media was equal to or greater than that of those cultured in a control medium of perlite-sand. Plant growth in fresh bark was inhibited initially and then recovered. Zn concentration and total content per plant were high for plants cultured in bark media even when little or no Zn was applied. The intereaction between media and applied Zn was significant. Plant Zn increased with increasing amount of applied soluble Zn when cultured in perlite-sand, but did not normally change for plants cultured in bark. High Zn concentration of plants cultured in fresh bark was too low to account for the initial growth inhibition. N concentration and content per plant were normally lower for plants grown in fresh bark. N of plants in aged bark was similar to plants in the standard medium. Growth inhibition of plants in fresh bark did not appear to be due to N deficiency.
Abstract
15N-labeled potassium nitrate was applied in a foliar spray to French prune/Marianna 2624 trees (Prunus domestica L.), and the nitrogen absorbed by the leaves was quantified. Nitrogen derived from a single foliar spray averaged 3% of total leaf nitrogen. L77, a non-ionic organosilicone surfactant which lowers surface tensions of aqueous solutions sufficiently for stomatal penetration, significantly enhanced the rate of NO3 absorption and increased incorporation of foliar-derived nitrogen into alcohol insoluble macromolecules. This enhancement was not apparent when labeled NO3 was applied with Regulaid, a carbohydrate-based non-ionic surfactant. About 25% of the foliar-derived N was apparently transported from leaves within 3 days when the stomatal penetrant was employed. No transport was evident in the absence of the penetrant.