A heat flow theory has been developed which can be used to predict freezing and thawing cycles of a temperate soil. The latent heat of fusion is incorporated into the classical heat flow equation with the heat capacity and the thermal conductivity of the soil modified to include terms which account for the phase transformation. Computations for a Palouse silt loam soil show that the ice‐liquid phase transformation occurs over a defined temperature range where the apparent heat capacity and the apparent thermal conductivity may take on values which are several orders of magnitude larger than those either in the unfrozen or in the near completely frozen soil. The computations also indicate that the presence of solutes in the soil water significantly lowers the temperature range over which the freeze‐thaw zone develops and may allow considerable transport of water and heat at lower temperature than in the absence of solutes.

No abstract

No abstract

The current Hungarian Soil Classification System (HSCS) was elaborated during the 1960s, based on the genetic principles of Dokuchaev. It was developed before sufficient data and modern data processing tools were available and served different purposes than current users need or apply it for.The central unit is the soil type, grouping soils that were believed to have developed under similar soil-forming factors and processes. The major soil type is the highest category that groups soils based on climatic, geographical and genetic bases. Subtypes and varieties are distinguished according to the assumed dominance of soil-forming processes and observable/measurable morphogenetic properties. STEFANOVITS (1963) defined the 23 soil-forming processes that have a dominant impact on the differentiation of the 39 soil types of the system.Based on accumulated data and experience, as well as on numerical tools for defining taxonomic relationships a modernization process was carried out. The process included: linking processes to diagnostics, review and numerical study of similarities and dissimilarities of existing units, development of new central units, development of a computer assisted key, and definition of methodology to derive the lower level units. The new, 15 soil types are defined by stronger morphogenetic and measurable criteria, but with the application of legacy data and the developed key, the earlier units can be converted to the new ones, hence the value of legacy data can be preserved.

Excessive radiant heat load limits the growh of plants in dryland farming during the rainless summer. The use of reflectants to control the radiation balance in field conditions is examined here. Modifications of the solar radiation balance in a wide‐row sorghum [Sorghum bicolor (L.) Moench ‘726’] crop grown on a dark brown grumusol (Chromoxererts) were obtained by spraying a white kaolin suspension on 1,000 m2 field plots. Treatments consisted of separate applications of the kaolin on the foliage and on the soil surface, and combined applications on both the foliage and the soil. Radiation transfer equations were used to quantify the effect of the various treatments on the solar radiation absorption of the foliage, and of the soil. These equations account for the presence of direct and diffuse components in the downward solar flux and make specific reference to a simplified definition of the radiation scattering properties of the foliage and the soil. Measurements of the diurnal variation of the solar radiation reflection above each experimental plot and fisheye determinations of the foliage distribution validated the simplifying assumptions used in deriving the transfer equations. With some additional assumptions the equations are extended to predict absorption by the foliage and the soil from daily totals of the global radiation. The reflectivity of the foliage increased by 24% immediately after spraying kaolin on the canopy. A 17% increase persisted 5 weeks later. The corresponding seasonal net solar absorption was reduced by 6%. The soil treatment doubled the solar reflectivity of the soil, causing an 18% decrease of the solar absorption by the soil. The increased reflected solar flux from the soil surface was partly intercepted by the foliage, and produced a 9% increase of absorption by the foliage. The application of kaolin to both the foliage and the soil resulted in very little change in the absorption by the canopy, the whitening of the foliage being offset by the addition of the radiation reflected by the soil, but was most effective in increasing the solar reflection from the field. Larger reductions of the canopy solar radiation balance can be expected by improving the dispersion of the kaolin coating on the entire foliage.