The level of CO₂ and of subsoil density were varied in a growth chamber study of the interaction of these two factors on root growth of cotton seedlings at constant O₂ concentration. At very low density root elongation rate decreased progressively with increasing CO₂, although moderate to good growth occurred even at 24% CO₂, the highest concentration used. At higher subsoil level densities, CO₂ had little effect on root penetration. Retardation by CO₂ was somewhat more severe for roots growing into solution culture than for those growing into loose subsoil, indicating that application of results of aeration experiments in nutrient solution to soils should be made with caution. Results suggest that in well-drained, medium-to-coarse-textured soils such as the Norfolk, CO₂ will seldom be a limiting factor for root growth even in compacted zones near the surface. The mechanical impedance of such zones, will definitely restrict root penetration and proliferation in subsoils.

SynopsisSoil moisture was estimated under a meadow crop for different periods during the growing season. The potential rate of evapotranspiration was estimated from Class A open-pan evaporation data. Stage of plant development and soil moisture stress factors were included in the prediction technique.

In recent years, economists have become much interested in recursive models. This interest stems from a growing need for long‐term economic projections and for forecasting the probable effects of economic programs and policies. In a dynamic world, past and present conditions help shape future conditions. Perhaps the simplest recursive model is the two‐dimensional “cobweb diagram,” discussed by Ezekiel in 1938. The present paper attempts to generalize the simple cobweb model somewhat. It considers some effects of price supports. It discusses multidimensional cobwebs to describe simultaneous adjustments in prices and outputs of a number of commodities. And it allows for time trends in the variables.

SynopsisThe highest yield was obtained on the 5370 water-stable aggregate treatment , indicating that natural aggregate stability levels may have been higher than those required for optimum yield of corn tops. Corn roots growing in conjunction with the soil microorganisms depleted the oxygen supply of the soil air to somewhat lower values than did the organisms alone. Rate of oxygen use per cc. of roots was greatest at higher oxygen levels and fell off sharply with decrease in oxygen content of soil air.

Merchantable volume growth in a managed southern pine forest was measured every 3 years from 1940 through 1960. Available soil moisture in the surface foot was estimated for each day of the 21 growing seasons. The soil-moisture estimates were combined with estimates of potential evapotranspiration to calculate indexes of potential growth. Linear regressions of measured growth on calculated potential growth explained 95 to 97% of the variation about the regression lines. With sufficient soils information and past measurements of growth, foresters may be able to estimate current annual growth in timber stands.

The processes involved in Mo availability to corn and soybeans growing in soil were investigated. Both mass-flow and diffusion were involved. Mass-flow caused Mo to accumulate at or in the root when the saturation extract contained more than 4 ppb. Mo. Diffusion patterns were usually obtained by autoradiographic procedures when the content was below 4 ppb. The saturation extracts of the soils investigated ranged from 2.2 to 8.1 ppb. Mo. The content of labile Mo in the soil varied from 41 to 211 ppb. of soil. The values of Dp/b for Mo varied from 0.5 to 8.4 × 10⁻⁷cm.² sec.⁻¹ and were much larger than for phosphorus.

To determine how manipulation of vegetative cover affects soil-moisture storage, 8 plots were laid out in a 50-acre block on the Coastal Plain of New Jersey, 4 on Lakeland sand and 4 on Lakehurst sand. Each plot, about 1/100 acre in size, was subdivided into 3 subplots, each of which was sampled gravimetrically 42 times over a period of 3 growing seasons. A relationship between bulk density and soil depth plus stone content was developed. From this, bulk density was estimated for each sample in five 1-foot layers. Moisture content by weight for each 1-foot layer was converted to moisture content by volume by applying the respective estimated bulk densities. Variations within and between the relatively close-spaced plots are presented for estimated bulk density and moisture content by voulme for each of the 1-foot layers.