Browsing by Author "Righetti, Timothy L."

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    Analysis of ratio-based responses
    (AMER SOC HORTICULTURAL SCIENCE, 2007) Righetti, Timothy L.; Sandrock, David R.; Strik, Bernadine; Vasconcelos, Carmo; Moreno, Yerko; Ortega Farias, Samuel; Banados, Pilar
    It is not appropriate to compare ratio-based expressions for different cultivars or treatments if a plot of the denominator versus the numerator of a ratio-based expression has a nonzero y-intercept and the values for either the denominators or numerators differ with cultivars or treatments. Whenever nonzero y-intercepts are encountered, the value for a ratio-based expression will be dependent on both the denominator and numerator. The "ratio problem" is demonstrated with shoot N concentration in blueberries (Vaccinium corymbosum L.) and amino acid accumulation in almonds [Prunis dulcis (Mill.) D.A. Webb]. Data were collected from the first and second growth flush of blueberry shoots on plants that were at two in-row spacings and two rates of N fertilizer. Free amino acid:total amino acid ratios were measured in dormant almond trees fertilized at different rates with and without foliar N supplements. Functions describing the relationship between dry weight and total N content in blueberry tissues have positive y-intercepts for both N fertilizer application rates. Functions describing the relationship between total amino acids and free amino acids in almond trees have a negative y-intercept. Differences attributable to fertilization rate in blueberries probably were the result of differences in N uptake and N utilization, but the effects of spacing and growth flush are indirect and can be accounted for by differences in dry weight. Likewise, effects of fertilization rate and foliar N supplement in almonds are indirect and can be accounted for by differences in the total amino acids in dormant trees. With regression one can determine if the relationship between the denominator and numerator differs for the groups or treatments being studied. When an analysis of covariance is used to account for differences in the denominators of ratio-based expressions, results are consistent with the regression analysis. When a conclusion is based on statistical differences of a ratio-based expression, it is the researcher's responsibility to determine whether these effects are direct or indirect.
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    Assessments CO2 assimilation on a per-leaf-area basis are related to total leaf area
    (AMER SOC HORTICULTURAL SCIENCE, 2007) Righetti, Timothy L.; Vasconcelos, Carmo; Sandrock, David R.; Ortega Farias, Samuel; Moreno, Yerko; Meza, Francisco J.
    Net photosynthetic rates often are dependent on leaf size when expressed on a leaf-area basis (CO2 assimilation as ULMOI(.)m(-2.)s(-1)). Therefore, distinguishing between leaf-size-related and other causes of differences in net photosynthetic rate cannot be determined when data are presented on a leaf-area basis. From a theoretical perspective, CO2 assimilation expressed on a leaf-area basis (mu mol(.)m(2.)s(1)) will be independent of leaf area only when total net CO(2)assimilation (leaf CO(2)assimilation as mu mol(.)s(-1)) is linearly related to leaf area and the function describing this relationship has a nonzero y intercept. This situation was not encountered in the data sets we evaluated; therefore, ratio-based estimates Of CO2 assimilation were often misleading. When CO2 assimilation data are expressed on a per-leaf-area basis (the standard procedure in the photosynthesis literature), it is difficult to determine how photosynthetic efficiency changes as leaves or plants mature and difficult to compare the efficiency of treatments or cultivars when leaf size or total plant leaf area varies.
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    Response of Highbush Blueberry to Nitrogen Fertilizer During Field Establishment, I: Accumulation and Allocation of Fertilizer Nitrogen and Biomass
    (AMER SOC HORTICULTURAL SCIENCE, 2012) Pilar Banados, M.; Strik, Bernadine C.; Bryla, David R.; Righetti, Timothy L.
    The effects of nitrogen (N) fertilizer application on plant growth, N uptake, and biomass and N allocation in highbush blueberry (Vaccinium corymbosum L. 'Bluecrop') were determined during the first 2 years of field establishment. Plants were either grown without N fertilizer after planting (0N) or were fertilized with 50, 100, or 150 kg.ha(-1) of N (50N, 100N, 150N, respectively) per year using N-15-depleted ammonium sulfate the first year (2002) and non-labeled ammonium sulfate the second year (2003) and were destructively harvested on 11 dates from Mar. 2002 to Jan. 2004. Application of 50N produced the most growth and yield among the N fertilizer treatments, whereas application of 100N and 150N reduced total plant dry weight (DW) and relative uptake of N fertilizer and resulted in 17% to 55% plant mortality. By the end of the first growing season in Oct. 2002, plants fertilized with 50N, 100N, and 150N recovered 17%, 10%, and 3% of the total N applied, respectively. The top-to-root DW ratio was 1.2, 1.6, 2.1, and 1.5 for the 0N, 50N, 100N, and 150N treatments, respectively. By Feb. 2003, 0N plants gained 1.6 g/plant of N from soil and pre-plant N sources, whereas fertilized plants accumulated only 0.9 g/plant of N from these sources and took up an average of 1.4 g/plant of N from the fertilizer. In Year 2, total N and dry matter increased from harvest to dormancy in 0N plants but decreased in N-fertilized plants. Plants grown with 0N also allocated less biomass to leaves and fruit than fertilized plants and therefore lost less DW and N during leaf abscission, pruning, and fruit harvest. Consequently, by Jan. 2004, there was little difference in DW between 0N and 50N treatments; however, as a result of lower N concentrations, 0N plants accumulated only 3.6 g/plant (9.6 kg-ha(-1)) of N, whereas plants fertilized with 50N accumulated 6.4 g/plant (17.8 kg.ha(-1)), 20% of which came from N-15 fertilizer applied in 2002. Although fertilizer N applied in 2002 was diluted by non-labeled N applications the next year, total N derived from the fertilizer (NDFF) almost doubled during the second season, before post-harvest losses brought it back to the starting point.
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    Response of Highbush Blueberry to Nitrogen Fertilizer during Field Establishment-II. Plant Nutrient Requirements in Relation to Nitrogen Fertilizer Supply
    (AMER SOC HORTICULTURAL SCIENCE, 2012) Bryla, David R.; Strik, Bernadine C.; Pilar Banados, M.; Righetti, Timothy L.
    A study was done to determine the macro- and micronutrient requirements of young northern highbush blueberry plants (Vaccinium corymbosum L. 'Bluecrop') during the first 2 years of establishment and to examine how these requirements were affected by the amount of nitrogen (N) fertilizer applied. The plants were spaced 1.2 x 3.0 m apart and fertilized with 0, 50, or 100 kg.ha(-1) of N, 35 kg.ha(-1) of phosphorus (P), and 66 kg.ha(-1) of potassium (K) each spring. A light fruit crop was harvested during the second year after planting. Plants were excavated and parts sampled for complete nutrient analysis at six key stages of development, from leaf budbreak after planting to fruit harvest the next year. The concentration of several nutrients in the leaves, including N, P, calcium (Ca), sulfur (S), and manganese (Mn), increased with N fertilizer application, whereas leaf boron (B) concentration decreased. In most cases, the concentration of nutrients was within or above the range considered normal for mature blueberry plants, although leaf N was below normal in plants grown without fertilizer in Year 1, and leaf B was below normal in plants fertilized with 50 or 100 kg.ha(-1) N in Year 2. Plants fertilized with 50 kg.ha(-1) N were largest, producing 22% to 32% more dry weight (DW) the first season and 78% to 90% more DW the second season than unfertilized plants or plants fertilized with 100 kg.ha(-1) N. Most DW accumulated in new shoots, leaves, and roots in both years as well as in fruit the second year. New shoot and leaf DW was much greater each year when plants were fertilized with 50 or 100 kg.ha(-1) N, whereas root DW was only greater at fruit harvest and only when 50 kg.ha(-1) N was applied. Application of 50 kg.ha(-1) N also increased DW of woody stems by fruit harvest, but neither 50 nor 100 kg.ha(-1) N had a significant effect on crown, flower, or fruit DW. Depending on treatment, plants lost 16% to 29% of total biomass at leaf abscission, 3% to 16% when pruned in winter, and 13% to 32% at fruit harvest. The content of most nutrients in the plant followed the same patterns of accumulation and loss as plant DW. However, unlike DW, magnesium (Mg), iron (Fe), and zinc (Zn) content in new shoots and leaves was similar among N treatments the first year, and N fertilizer increased N and S content in woody stems much earlier than it increased biomass of the stems. Likewise, N, P, S, and Zn content in the crown were greater at times when N fertilizer was applied, whereas K and Ca content were sometimes lower. Overall, plants fertilized with 50 kg.ha(-1) N produced the most growth and, from planting to first fruit harvest, required 34.8 kg.ha(-1) N, 2.3 kg.ha(-1) P, 12.5 kg.ha(-1) K, 8.4 kg.ha(-1) Ca, 3.8 kg.ha(-1) Mg, 5.9 S, 295 g.ha(-1) Fe, 40 B, 23 g.ha(-1) copper (Cu), 1273 g.ha(-1) Mn, and 65 g.ha(-1) Zn. Thus, of the total amount of fertilizer applied over 2 years, only 21% of the N, 3% of the P, and 9% of the K were used by plants during establishment.