Water retention and hydraulic conductivity of a loamy sand soil as influenced by crop rotation and fertilization

Measurements are reported of soil organic carbon content, dry bulk density, water retention characteristics, and saturated hydraulic conductivity of a sandy loam soil with two different crop rotations and two levels of fertilization. The water retention characteristics were fitted to the van Genuchten equation. Values of unsaturated hydraulic conductivity were estimated by calculation. It was found that crop rotation has much larger effects on these soil physical properties than fertilization. Water retention and hydraulic conductivity are greater when mustard, and clover with grass are included in the crop rotation, but only at water contents greater than 0,10 and 0, 13 kg kg^?1respectívely.     

Relationships between dough strength,polymeric protein quantity and composition for diverse durum wheat genotypes

Five different Glu-B1 HMW-GS patterns were identified among a collection of diverse durum wheat genotypes grown in 2001 in two locations in western Canada. The durum wheat lines exhibited a wide range of dough and gluten strength characteristics as measured by alveograph and 2 g mixograph parameters, gluten index (GI), and protein composition as measured by unextractable polymeric protein (UPP) content and the ratio of high-molecular weight (HMW) glutenin subunits (GS) to low-molecular weight (LMW) GS. HMW-GS subunits patterns represented within the genotypes were 6+8, 7+8, 7+16, 14+15 and 20. Two of the genotypes expressed Glu-A1 HMW-GS 2* in combination with other HMW-GS. Approximately 95% of the durum genotypes were γ-gliadin 45 types. Analysis of variance indicated that genotype was a greater source of variation in all measurements than was growing location, with the exception of protein content which showed less variation contributed by genotype and more contributed by location than for other quality parameters. UPP was strongly associated with all strength measurements. All of the γ-gliadin 42 types were low in UPP and weak. Among the γ-gliadin 45 types, those possessing HMW-GS 20 were typically in the lower half of the UPP and strength range. There was no clear evidence of an association between any of the other HMW-GS patterns and gluten strength. The majority exhibited HMW to LMW-GS ratios that were within the relatively narrow range of 0.15–0.25, yet there were wide variations in dough strength among genotypes within that range. Increasing proportions of HMW-GS resulting in ratios of greater than 0.30 were generally associated with weak dough and gluten and low UPP content.     

Morphological Changes of the Endometrial Epithelium in the Bitch during Metoestrus and Anoestrus

Although cyclic changes of the endometrium in dogs involving both stromal and glandular compartments have been described, the fate of the surface epithelium after progressive growth and secretion is still unclear. In the present study, uteri of 43 healthy bitches in metoestrus and anoestrus were examined macroscopically and histologically. Tissue biopsies were taken from three different locations (cranial and middle parts of uterine horns and bifurcation). The stage of the oestrous cycle was determined by evaluation of progesterone and oestradiol levels in plasma hormone and was also confirmed clinically. Crypts formed in the luteal phase were covered with a columnar epithelium which gradually underwent fatty degeneration. In addition, the stromal part of the crypts disappeared and finally, in early anoestrus, epithelial sheaths desquamated and shed off into the uterine lumen. The surface epithelium was replaced by new cuboidal cells proliferating and migrating from the glandular openings. These findings were confirmed by oil red O staining and immunohistochemical detection of proliferation with Ki‐67 marker.     

Radial pressures generated by the earthworm Aporrectodea rosea

Summary The radial pressures generated by the earthworm Aporrectodea rosea were measured in a study of the conditions under which the worms were able to crack soil discs into which they were encouraged to tunnel. The tensile strength of replicate discs was determined by indirect tension tests and by expansion of rubber membranes in soil discs. Simple engineering theory was used to relate the stress required to fracture a disc with the applied internal stress. Mean values for the radial stress applied by the earthworms in tunnelling through the discs was 230 kPa. With some assumptions about the distribution of muscles across the worm diameter, it was estimated that the mean maximum force generated by all the longitudinal muscles in any segment was 3.2 N.     

Influence of biopores on root growth,water uptake and grain yield of wheat (Triticum aestivum) based on predictions from a computer model

Summary The use of vertical biopores by wheat (Triticum aestivum) seminal roots for easy access to the subsoil and the consequences for plant water supply and yield has been investigated by computer simulation. Parameters included were: biopore density and diameter, depth of cultivation and strength of the subsoil — all under a wide range of seasonal weather conditions. The model predicts that biopores add significantly to root penetration at depth, even at a density of 0.1% v/v of small, vertical pores, while 1.5% to 2.0% v/v can ensure maximum root penetration. When the growing season is shorter a larger number of biopores is needed to ensure timely root penetration to depth. With shallow tillage, biopores occur closer to the soil surface, and their importance is increased. Deeper root penetration invariably gives greater water uptake and transpiration, but may have a negative effect on grain yield, especially under the driest climatic conditions. An increase in early water use may result in less soil water being available during the grain-filling period. The effect of biopores on plant transpiration varies from year to year, depending on the amount of rain and its distribution in time, and on the amount of soil water stored at time of sowing.     

Advances in characterization of soil structure

Soil structure is defined as “the spatial heterogeneity of the different components or properties of soil”. Aspects of soil structure which are important for plant development, soil water balance and soil workability are reviewed briefly. The different types of soil structure which occur on different size scales are placed in a hierarchical order. Different mechanisms give rise to the different hierarchical orders. Similarly, different physical/chemical/biological processes are involved in the stabilization of the different hierarchical orders.A number of methods for measuring soil structure are described. Preference is given to methods involving direct observation of structural features by scanning electron microscopy and by optical scanning of impregnated sections and fracture surfaces. These need to be supported by assessments of the stabilities of compound particles in water and of the mechanical strengths of compound particles as a function of water content.“Good” soil structure is described as one where all the hierarchical orders are well-developed and stable. The greatest lack of knowledge appears to be in the 2–100 μm size range which is too large to have been studied by colloid chemists and too small to be visible to the naked eye. It is suggested that more observations of soil structure should be made in this size range, as it may hold many important clues on how to manage soil structure in the field.     

Effect of soil structure on wheat root growth, water uptake and grain yield. A computer simulation model

A model for simulation of wheat root growth under non-optimal conditions has been developed. The following influences on root growth are considered: soil temperature; soil water suction and mechanical resistance dependent on soil density and soil water content; the occurrence of soil cracks. The probability of root tips finding cracks, where unimpeded growth can occur, is given special consideration, including the effect of changes in the crack system with changes in soil water content. Water uptake is calculated, and by use of a transpiration coefficient an estimate of dry-matter production is made. This is partitioned between roots, leaves and stem and later grain. Effects of soil fertility are not yet considered in this model.A sensitivity analysis of the model was made by varying the soil density profile, the occurrence of cracks, sowing date and plant density for several years of weather data. The variability, caused by the fact that only a limited number of root axes was simulated in each run and guided by random numbers, was also investigated.The model can be used to assess the effects of compaction on wheat yield, and also the likely benefits which may be derived from sub-soiling or slit-tillage.The model is written in Digital's VAX FORTRAN language, and a run for one growing season takes less than 10 seconds of CPU-time on a VAX 11/785 computer.