Search Results

You are looking at 1 - 4 of 4 items for

  • Author or Editor: J.P. Pearson x
Clear All Modify Search

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

A study was undertaken to determine the seasonal dynamics of leaf and fruit K content and the influence of tree K status and fruit growth on leaf and fruit K accumulation rates in French prune (Prunus domestics L. cv. d'Agen). Mature trees in a commercial orchard were treated with various rates of K2 SO4. (O to ≈20 kg/tree) in the fall. Fruit dry weight yield per tree at harvest and fruit K content were higher for high-K trees, but fruit percent K (by dry weight) was ≈1.0% for all trees. Leaf scorch and subsequent abscission severely reduced the canopy of K-deficient trees. Significant positive linear relationships between leaf and fruit K accumulation rates existed for the periods of 28 Apr.-28 May (May) and 28 May-7 July (June). A significant negative linear relationship existed between these two criteria from 7 July-3 Aug. (July). May (0.237 mg K per fruit-day) and July (0.267 mg K per fruit-day) mean fruit K accumulation rates were similar, but both were significantly higher (P = 0.001) than those for June (0.140 mg K per fruit-day). Mean leaf K accumulation rates for May (- 0.007 mg K per leaf-day) and July (-0.010 mg K per leaf-day) were similar, but both were significantly (P = 0.001) less than for June (0.005 mg K per leaf-day). Potassium per fruit accumulation was highest in trees with highest K status. Periods of net leaf K efflux and influx did not precisely correlate with fruit growth stages measured by fruit dry weight. The period of lowest fruit K accumulation (28 May-7 July) coincided with the period of maximum dry matter accumulation by the kernel. After 7 July, all increases in fruit dry weight and K content were due to mesocarp growth.

Free access

The objective of these experiments was to determine if preemergence herbicides perform similarly across pine bark that was aged for varying lengths of time including 0, 4, 8, and 12 months after bark removal from harvested trees. Three preemergence herbicides were evaluated for three separate weed species, including 1) Cardamine flexuosa With. (bittercress) with isoxaben, 2) Digitaria sanguinalis (L.) Scop. (large crabgrass) with prodiamine, and 3) Oxalis stricta L. (woodsorrel) with dimethenamid-P. Leaching of herbicides through substrates was evaluated for prodiamine. Weed growth in the various substrates was variable, but few differences were detected in weed growth among the pine bark substrates evaluated. For isoxaben and prodiamine, weed control was similar among the pine bark substrates in most cases when label rates were applied. Although some differences were detected in prodiamine performance across different pine bark ages, a high level of control was achieved in all cases at rates well below manufacturer recommendations. Prodiamine leaching was minimal in all substrates. It would be recommended that growers test substrates for physical properties before use so that irrigation and other production inputs could be modified if needed. In most cases, growers should expect similar performance of preemergence herbicides regardless of pine bark substrate age.

Free access