Experimental on the forming mechanism of upland field soil moisture condition and its rational management to save water use and high quality production

It is generally said that soil moisture condition affects the quality and production of crop or vegetables. Therefore many considerations have been made on this theme. The aim of this study is operation of the mechanism of soil moisture condition formation in upland field and its rational management to save irrigation water and so on. Volume 1: Experimental Study on The Forming Mechanism of Soil Moisture Condition in Upland Fields. In the summer of 1994, drought injury in crops occurred due to high temperature and low rainfall throughout Japan. In this study, the author examined the characteristics of soil moisture condition and evapotranspiration to determine the water balance in a maize field during the drought. The results are summarized as follows: ①The total amount of soil moisture in the soil layer to a depth of 1.0m below surface throughout the growing season was less than the Depletion of water content for Optimum growth (DOG). And soil moisture was reduced even at a depth of 2.0m, primarily because of the rapid development of the maize root systems and water uptake. ②Characteristic of the energy balance in the maize field during the growing season under the drought conditions in this study were different from results reported by others for other crops, for example the intensity of latent heat flux approximated net radiation flux, and sensible heat flux was nearly or less than zero. ③Dry matter production, total digestible nutrients and some other components were less in 1994 than 1995, when those values were comparable to values during the normal year, despite the similarities between the two years in the weather conditions for the growth of maize. This difference may be due to the difference in total amount of soil moisture below the soil surface to a depth of 1.0m at the conclusion of Baiu, the rainy season. In 1995, the soil moisture condition was higher than DOG because of high rainfall during Baiu. ④On the bases of the above findings, the authors propose a simple irrigation method. When rainfall is insufficient at the end of the rainy season, field are irrigated only a time as soon as possible to attain the field capacity in the soil layer to a depth of 1.0m below surface. Film mulch is being used in many farm lands because it improves the environment for cultivation by suppressing water evaporation from soil surface, maintaining a mild soil moisture condition, and maintaining the soil temperature higher than the bare soil surface, in addition to protecting against pests and diseases. Crop cultivation in cool high lands (such as the Shinshu Plateau) can be made possible with the introduction of film mulch. However, as the direct infiltration in the root zone are lower in fields where film mulch is used than in bare soil fields, and this raises fears that droughts would be exacerbated. Experimental comparisons of the soil moisture condition and flow between mulched bed and furrow space using the soil moisture measurement technique at many positions and many depths were carried out in the fall of 1995 in field planted with Chinese cabbage (Brassica pekinensis Rupr.), and in the spring of 1996 in field planted with cabbage (Brassica oleracea L.). The results are summarized as follows; ①The shallow topsoil of the mulched beds had less soil moisture than furrow space and bare soil even after light rains at low soil moisture condition. The sowed areas (hole of the mulch film) in mulched beds, however, were moister than the surrounding of sowed area. But one or two days after rainfall, soil moisture condition in mulched bed and furrow space were almost same. ②As the crops grew, the soil moisture became lower than furrow space due to the water uptake by the crops' root system. In the soil layer below the root zone, i.e. at a depth of more than 0.3m, soil moisture is moved from the furrow space to the mulched bed by the gradient of soil moisture potential ⊿ψ caused by the soil moisture uptake by the root system. Volume 2: Experimental Study on The Rational Management of Soil Moisture Condition to Save Irrigation Water and Rise the Crops Production and Quality. High temperature and low rainfall created drought conditions in most of Japan during the summer of 1994. The authors measured soil moisture condition and evapotranspiration (ET) rates during that time. Suzuki and Nakayama (1996) showed that the ET rate in maize under drought conditions remained constant despite the soil moisture declining to below the level for optimum growth. They explained this observation result by the rapid development of the maize root system to uptake sufficient soil moisture. In this section, the author developed a method to estimate ET in maize fields under drought conditions for determination of the optimum amount of irrigation water. The observations were carried out at the research farm of Shinshu University, on a mountain foot in Japan's Chuo Alps. The 2.5ha experimental site was planted with maize (p3732, Yukijirusi ...