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  • Author or Editor: A. R. Renquist x
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Abstract

Red raspberry (Rubus idaeus L.) is prone to a “white drupelet” disorder on the sun-exposed side of the fruit, largely during those harvest periods when daytime temperatures exceed about 33°C. In mid-August, more than 40% of the fruit were affected. Three types of shade covers (30% and 60% black shade fabric and 25% shade white polyester), placed over raspberry plots for 1 to 3 weeks prior to fruit harvest, reduced the amount of solar-injured fruit from 41% in unshaded plots to between 8% and 16%. Fruit surface temperature was reduced about 4° by both black shade fabrics, but only 1° by the polyester cover. Fans cooled fruit by about 2°, but the reduction in solar injury was less than with shade covers.

Open Access

Economic and environmental concerns have increased the need for quantitative advice on fertilizer rates. In addition, it would aid researchers to be able to estimate the degree to which nutrient availability is affecting yield in a wide variety of field experiments. All of these needs can, in principle, be addressed using the new PARJIB model. PARJIB retains the functional simplicity of much earlier analytical models of crop responses to soil test values and fertiliser application rates. However, in a key departure from previous approaches, response to scaled nutrient supply indices is dictated by the potential yield adjusted for plant population and water stress. The version currently being evaluated simulates responses to supply of N, P, K and Mg, varying either singly or in combination. We have calibrated the model for sweet corn, carrots, and snap bean crops grown under temperate conditions in a wide range of soils. Simulated yields agreed well with observed values; the root mean square error was 8% to 13%, and regressions of observed against simulated yields passed through the origin with slopes that were not significantly different from 1. After calibration, the model predicted strong interactions between nutrient supply, plant population and water stress. PARJIB appears to have substantial potential to improve nutrient management for horticultural crops.

Free access

Abstract

A computer model was developed to predict autumn vegetative maturity, end of summer dormancy of red-osier dogwood (Cornus sericea L. syn. Cornus stolonifera Michx.). Empirical equations were developed from growth chamber data and applied to results obtained from lath house grown plants. The model required input parameters of 2-hourly temperatures and daylengths. From the data daily phototemperature values were determined. The empirical model over-estimated the time to maturity of the lath house grown plants by only 4 days, perhaps indicating the need for a more precise measure of the critical photoperiod.

Open Access

Abstract

Flowering, fruit set, fruit size, and bearing potential are the main components of tree fruit and nut yield. The contributions of the individual components to yield and their interrelationships must be clearly defined in research addressing tree fruit productivity. Researchers have been inconsistent in terminology and procedures used to evaluate treatment effects on the major yield components. Although the relative effect of a treatment may be evident within an individual study, standardized measuring and reporting procedures are necessary if one wishes to compare results within the same species from various investigators, locations, and disciplines.

Open Access