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Jongtae Lee, Jinseong Moon, Heedae Kim, Injong Ha and Sangdae Lee

increased with added N fertilizer, whereas P and K uptakes in bulbs were lowest at the 0 N rate ( Table 4 ). However, fertilizer use efficiency of N was 36.0% in the 120 kg·ha −1 treatment followed by 240 kg·ha −1 at 28.0% and 360 kg·ha −1 at 20.6%. On

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Tyler C. Hoskins, James S. Owen Jr. and Alex X. Niemiera

, and improvements in fertilizer use efficiency may help growers maintain profitability as fertilizer costs increase. Second, reducing the runoff nutrient load minimizes non-point source agrichemical contributions to local watersheds while simultaneously

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L. Espinoza, C.A. Sanchez and T.J. Schueneman

Four field experiments were conducted during two production seasons to evaluate soil-test P fertilizer recommendations for celery (Apium graveolens var. dulce) produced on Histosols, which often are linked hydrologically to environmentally sensitive wetlands, and to evaluate band placement as a strategy for improving P fertilizer-use efficiency in celery in such areas. Phosphorus was applied (broadcast or banded) at 0,50, 100,150, and 200 kg P/ha. Broadcast P was surface-applied and disked into the soil ≈ 15 cm deep 1 day before planting. Banded P was applied 5 cm below the soil surface and 5 cm to the side of each celery row. Total above-ground mass, marketable trimmed yield of celery, and yield of the larger grade sizes increased with P rate in all experiments. Band P placement was not a viable strategy for improving P fertilizer-use efficiency for celery. However, our results indicate that previous soil-test-based P fertilizer recommendations for celery were too high for the cultivars grown currently, and improved P fertilizer-use efficiency can be obtained with revised soil-test calibrations.

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Raul I. Cabrera, Richard Y. Evans and J. L. Paul

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.

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Mohamed Benmoussa and Laurent Gauthier

In soilless culture, the buffering capacity of the root environment for nutrients is low. This, combined with fluctuations of climatic factors and changes in nutrient uptake rates, can lead to nutrient imbalances. In order to achieve high yield and better quality, it is necessary to keep the nutrient concentrations in the root environment at the target levels. This requires frequent analysis and adjustments to the nutrient solution. Currently, leaching of the growing media or renewal of the nutrient solution is commonly used to avoid accumulation or depletion of nutrient in the root environment. However, this practice lowers the efficiency of fertilizers and can lead to the contamination of the ground water. One way to remedy to this problem is through the use of nutrients uptake models to track the composition of the nutrient solutions. The objective of this study was to develop such models. Such models can be used to maintain balanced nutrient solutions for longer periods. This can lead to reduced leaching and improved fertilizer use efficiency. Macronutrient (N, P, K, Ca, and Mg) uptake models were developed for tomato plants grown in an NFT system using data collected from experiments conducted in the Laval Univ. greenhouses. Analysis of the experimental results showed that the main factors affecting nutrients uptakes are light and transpiration.

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J.P. Mitchell, S.E. Allaire-Leung, B.L. Sanden and L. Wu

Optimal water management is essential in irrigated agricultural regions to sustain productivity, conserve water resources and protect groundwater quality. The southern San Joaquin Valley (SJV) of California is a major irrigated production region in which solid set sprinkler systems are commonly used to grow such crops as carrots (Daucus carota L.), potatoes (Solanum tuberosum L.), garlic (Allium sativum L.) and onions (Allium cepa L.) in predominantly sandy soils. Water and fertilizer use efficiencies are important concerns in this region. In 1996 and 1997, we evaluated the effects of three sprinkler spacings [32.2, 38.6 and 45 ft (9.8, 11.8 and 13.7 m)] and irrigation uniformity within these spacings on carrot yield, quality and nitrogen content. Applied water and soil nitrate and ammonium contents were monitored at four locations within each sprinkler lateral spacing throughout both seasons. Neither sprinkler spacing nor location within a given sprinkler spacing affected carrot production or quality. Distributions of soil nitrate and ammonium resulting from the different sprinkler spacings were also not correlated with carrot yields. These results suggest that any of the three spacings can be used for high carrot quality and productivity.

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Raul I. Cabrera, Richard Y. Evans and J. L. Paul

Nitrogen leaching losses of 21, 40 and 49% were measured from container-grown `Royalty' roses irrigated for one year with nutrient solutions containing 77, 154 and 231 mg N/l. There were no significant differences in number of flowers per plant or dry matter per plant. The N present in the harvested flowers accounted for 43, 27 and 17% of the N applied for the 77, 154 and 231 mg N/l treatments, respectively.

Plants receiving 154 mg N/l at leaching fractions of 0.1, 0.25 and 0.5 had corresponding N leaching losses of 22, 38 and 56%. In this experiment, however, the 0.5 leaching fraction produced yields significantly higher than those of the 0.1 and 0.25 treatments. The N recovered in the harvested flowers accounted for 28, 25 and 19% of that applied to the 0.1, 0.25 and 0.5 treatments, respectively.

The results of these studies suggest that modifications in current irrigation and fertilization practices of greenhouse roses would result in a considerable reduction of N leaching losses and enhance N fertilizer use efficiency, without loss of cut flower yield and quality.

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Jonathan Frantz and Peter Ling

Bedding plant petunia (Petunia ×hybrida) is often produced with high nutrient concentrations as a cool-season crop. How a plant uses the nutrients supplied will depend in large part on the environmental factors influencing growth rate, such as light and CO2. Since more growers are considering using supplemental CO2 to improve energy efficiency for plant production, it is important to understand light and fertilizer levels needed for efficient production of high-quality plants. Using a multi-chamber controlled environment system, petunia plants were grown from seed for 6–8 weeks after transplanting into different light and CO2 environments and fed with either a low (7.1 mM N) or high (21.3 mM N) fertilizer regime. Plants were evaluated for appearance, harvested periodically, and separated into flower, stem, and leaf biomass. Biomass was then dried and analyzed with ICP-OES for essential macro- and micronutrients. Low-fertilizer-grown plants had consistently earlier and more flowers, but showed symptoms of nutrient deficiencies in the final few weeks of production at all light and CO2 levels. There were significant interactions between light and fertilizer treatments for different nutrients. Calcium uptake was greatly influenced by light level, Fe, P, and K were influenced by the fertilizer supply, and Mg and B were inversely influenced by fertilizer supply at high light. These data suggest new management strategies are needed to improve fertilizer use efficiency in different environments.

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N. M. El-Hout

Band placement has been recognized as an effective strategy for improving P fertilizer-use efficiency on Histosols, which are often characterized as environmentally sensitive wetlands, and for reducing P loading of drainage waters from these soils. Recent studies indicate that crisphead lettuce (Lacruca sativa L.) yields can be optimized with a band-P rate one-third of that required with broadcast applications. However, such findings have not been verified in large production plots. Five field experiments were conducted between 1991 and 1993 to evaluate the response of crisphead lettuce produced commercially on Histosols to band P rates. Liquid P fertilizers were placed in lo-cm-wide strips, 8.5-cm below the seed at planting in rates ranging from 0 to 224 kg P ha-1. Lettuce yields increased significantly with P rate in all experiments. Irrespective of initial soil-test-P index, lettuce yields within each experiment were maximized with a band rate 54% of that required in a broadcast. The pooled data for all experiments showed a similar trend. These findings provided a means of making alternative band fertilizer recommendations by utilizing an existing preplant broadcast soil test.

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B. Sanden, L. Wu, J.P. Mitchell, L. Pan and R. Strohman

This research tests the hypothesis that decreasing lateral spacing from 45 to 35 feet in solid-set sprinkler systems increases the uniformity of irrigation water distribution and improves water and N fertilizer use efficiencies. Three different spacings between sprinkler laterals (35', 40', and 45') were set up in three blocks in a 60-acre commercial carrot field in Western Kern County in California's San Joaquin Valley. Determinations of irrigation water distribution uniformity, yields, crop water use, plant growth, and nitrate leaching were made. Mean sprinkler distribution uniformities (DU) were found to be 80.6%, 78.1%, and 86% for the 35-, 40-, and 45-ft spacings, respectively. Total carrot yield and quality did not differ significantly among the three spacings, corroborating the finding that irrigation uniformities were similar among the treatments. Although the three lateral spacings evaluated in this initial experiment did not result in major differences in irrigation uniformity, total yields, or quality, the findings of this initial stage of our research are significant. They point to the need for new assessments of currently used protocols for evaluating sprinkler irrigation management of water and nitrogen fertilizer if they can be confirmed by repeated trials in coming years.