Effects of soil conditions on root system were reviewed. Soil type, fertilization, tillage and soil water condition affect total root length, root depth and specific root length of winter wheat. Significant difference in the root system was also found for some arable crops and genotypes. Idieal type of crop root system was discussed in relation to grain yield, grain quality and sustainable agriculture.
Methods for analyzing root system architecture and root distribution in soil are reviewed in relation to fractal geometry. Fractal dimension (D) is an useful index for describing root system morphology, as well as for quantification of topological architecture of the system. Fractal lacunarity and multifractal measure are applicable to root system analysis and they may offer alternative information on root system architecture.
Theoretical back-ground and principle of electro-physiological method for the study of root physiology were reviewed. The applicability of a model of electro-physiological structure to the root system in the field was experimentally examined and discussed. A convenient system via a perfect liquid junction was developed for long term measurement of trans-root electric potential (TRP) in field trees. The electro-radicogram of a kaki tree (Diospyros kaki) showed a regular diurnal changes. The seasonal change in the potential level and in the amplitude of oscillation was observed, and discussed in relation to the root activity and the environment.
We present neutron imaging of water in root-soil system by an X-ray film method as well as CT method. In the case of an X-ray film method, a soybean seedling grown in a thin aluminum container was fixed on an aluminum cassette and was irradiated for 19 seconds by thermal neutrons from a research reactor, JRR-3M, installed at Japan Atomic Energy Research Institute. The neutron flux from the reactor was 1.5X 108n/cm2・s. A gadolinium n/γ converter, which thickness was 25μm, and an X-ray film were sealed in vacuum in the cassette. To get a CT image, the soybean seedling grown in a cylindrical container was fixed on a rotating disk and was irradiated for 4 seconds per projection. The neutrons penetrating the sample was converted to photons by a fluorescence converter. The photon image was guided to a cooled CCD camera using two mirrors. The sample was rotated with an interval of 1 degree for 180 degree, i.e.180 images were obtained for the CT construction. Neutron beams allowed to image not only a root imbedded in soil but also water movement in the vicinity of the root. The method is nondestructive, therefore, morphological development of the root but also water movement near the root was able to be visualized. Through piling up the CT images, which were successively taken every 50μm, three dimensional water image of the root-soil system was constructed.
A large amount of nitrogen fertilizer has been applied in tea cultivation to produce the new shoots contained much amino acids. However the recovery rates of nitrogen by tea plants are comparatively low, and excessive application of nitrogen bring on the increase in nitrate concentration of the groundwater. It could be essential for the distributed region of root system magnification in tea plants by the the soil improvement before planting in tea gardens to increase the recovery rates of applied nitrogen. We estimated that the nitrate leaching rates from tea gardens was suppressed by the use of coated fertilizer and the application of fertilizer into surface soil by injection method.
Relationship between allophane content and physical properties for volcanic cohesive soil was investigated. The main results are as follows
1. Allophane clay minerals are the main factor for forming ped structures.
2. Acid dispersion is more effective than alkali dispersion when the allophane content is above 50%.
3. Natural water content, liquid limit, non-free water content and natural void ratio increasing linearly with allophane content respectively.
4. Volcanic cohesive soil lies below A-line in plasticity chart and fall more far from the A-line with increasing allophane content. The soil has its characteristic linear line in the chart.
5. Compacted dry density decreases linearly with increasing allphane content.
As Terra Roxa has a high clay content, and a lot of fissures occur in the surface soil under the no-tillage cropping in habitual drought terms, thus the root system of crops expands to the subsoil through the fissures. Under the tillage cropping, roots expand transversely among the granular structure of tilled soil layer. Roots can hardly penetrate through the underlying compact layer downward as there are only a few of finer fissures. For the non-tilled surface soil, fissures occur in the parts where hardening has been developed. Since the broken structure is preserved, the state of surface soil gets closer to that of tilled one by the accumulation of the structure as time goes by. An examination was conducted to make evident the process of nutrient supply to the subsoil which is brought about by falling of fertile surface soil into the fissures. Clods were collected from each soil horizon and fractionated samples were prepared ; i.e. the main bodies of clods and fine soil particles which adhered to the surfaces of clods and these were lightly scraped off with a metal brush from the surfaces. The contents of several nutrients were compared between the fine particle fraction and clod fraction at each horizon. Under the no-tillage cropping, generally, the nutrient content of fine particle fraction was higher than that of clod fraction, especially on K, Ca, and Mg. On the other hand, those differences were rather smaller under tillage cropping. Thus, under no-tillage cropping, falling of fertile surface soil was presumed but nutrient supply attributable to root decay was also suggested, because the content difference was found in the subsoil as well where the fissures became less and finer. Under the no-tillage cropping, improvements in the physical and chemical properties of subsoil are considered to be possible by such a mechanism mentioned above, with maintaining the surface soil in a fertile state.