Search Results

You are looking at 1 - 3 of 3 items for

  • Author or Editor: J.C. Ojala x
Clear All Modify Search
Authors: and

Abstract

Field studies were conducted in 1985 and 1986 to compare the effects of banded ammonium polyphosphate (APP) and acid urea phosphate (AUP) on P nutrition and yield of potatoes (Solanum tuberosum L. cv. Russet Burbank). The studies were conducted on a Declo silt loam containing 9% CaCO3 equivalent. Soil NaHCO3-P values were 6.9 and 12.1 mg·kg-1 in 1985 and 1986, respectively. Ammonium polyphosphate and AUP were applied at planting in bands above the seedpiece at 0, 60, and 120 kg P/ha in 1985 and 0, 40, and 80 kg P/ha in 1986. Nitrogen fertilizer was applied at a uniform rate of 240 kg N/ha. In both years, petiole P concentrations for the APP treatments were higher than those for the AUP treatments during most of the tuber growth period and tuber yields were 9% to 15% higher with APP than with AUP.

Open Access

Abstract

Regression models of potato (Solanum tuberosum L. cv. Russet Burbank) leaf water potential (ψleaf) were developed for irrigated conditions using concurrent measurements of total solar irradiance (Rs), air vapor pressure deficit (VPD), air temperature (Ta) and windspeed. Estimates of potential evaporation (Ep) also were related to ψleaf. The data were collected over a 3-year period from two locations in southern Idaho. Of the variables tested, Rs had the highest simple correlation with ψleaf (r = 0.93), although a slightly higher correlation was obtained for log-transformed values of VPD (1n VPD). Potato ψleaf was best described by the equation ψleaf = -0.3672 - 0.1959 In VPD – 0.0005 Rs, where ψleaf, VPD, and Rs are expressed in units of MPa, kPa and W·m–2, respectively. The model accounted for 95% of the variation in ψleaf for well-watered ‘Russet Burbank’ potatoes. When the model was tested on an independent data set, it estimated diurnal changes in ψleaf for several different cultivars to within ±0.1 MPa of the measured values. The relationship between ψleaf and Ep was nonlinear and was described by an exponential function. Estimates for the Ep model were nearly identical to those for the VPD Rs model when ψleaf values were below -0.3 MPa.

Open Access

Abstract

Reference values were derived from field data for use in evaluating the N, P, K, Ca, and Mg status of ‘Valencia’ orange (Citrus sinensis [L.] Osbeck) trees by the Diagnosis and Recommendation Integrated System (DRIS). DRIS diagnoses generally agreed with diagnoses made by the sufficiency range method, with the advantage that DRIS reflects nutrient balance, and identifies the order in which nutrients are likely to become limiting. DRIS diagnoses were affected by the type and age of the tissue sampled. DRIS reflected changes in nutrient concentrations due to alternate bearing or crop load effects and agreed with the sufficiency range method when concentration changes were sufficient to affect the latter method.

Open Access