A simple model of P uptake by crops as a possible basis for P fertilizer recommendations.

In the Netherlands the Pw value, based on an extraction of soil P with water, is used as a basis for P-fertilizer recommendations for arable crops. Using a simple, mechanistic model of P transport in the soil the Pw value required for adequate P uptake by crops can be calculated on the basis of daily uptake requirements, root area index, P-adsorption isotherms and total amount of P taken up during a growing season. Calculated Pw values for adequate uptake are in the same range as the present recommendation scheme based on field experiments. Possible refinements of the model are discussed. For each soil the Pw value can be calculated that corresponds to the P concentrations in the soil solution according to standards set to reduce environmental pollution. The model predicts that, unless the root area index of non-cereal crops is considerably improved, these standards cannot be met in the plough layer without affecting crop production levels. Calculations show that the present method of determining the Pw value yields a reasonable compromise between a measurement of intensity and capacity of P supply in the soil. (Abstract retrieved from CAB Abstracts by CABI’s permission)

A Comparison of Planting Stock Characterization with Root Area Index, Volume and Dry Weight

Volume, area and weight methods for characterizing tops and roots of coniferous nursery stock were compared for accuracy, reproducibility and practicality using 60 seedling samples of red pine (Pinus resinosa Ait.), white pine (Pinus strobus L.) and white spruce (Picea glauca (Moench) Voss). Root volume estimates as determined by the volume displacement method were as accurate and reproducible as root area index estimates determined by the rhizometer. Root volume determination was faster than root area index while producing information of comparable quality and usefulness. White roots measured by a rhizometer can be underestimated by as much as 50% when a high light intensity is used. Dry weight is a reliable indicator of biomass but is time consuming compared with either root volume or root area index.

Root biomass and surface area in three successional tropical forests

Total root biomass and surface area of fine roots (<5 mm diameter) were determined to a depth of 85 cm in 1-, 8-, and 70-year-old tropical forests on the same soil type (Typic Dystrandept) at Turrialba, Costa Rica. Root biomass and root area index (RAI) increased with age: biomass = 219, 1291, and 1555 g/m2, and RAI = 1.34, 4.66, and 5.28 in the 1-, 8-, and 70-year-old stands, respectively. Fine roots were most concentrated in the surface 5 cm of soil at all three sites, but especially so in the 70-year-old stand. The 1- and 8-year-old vegetations had proportionally more fine roots below 25 cm than the 70-year-old vegetation, but lacked the large-diameter roots characteristic of the 70-year-old stand.