Hydraulic and earth engineering – Drainage or irrigation
Reexamination Certificate
2002-06-24
2004-04-13
Pezzuto, Robert E. (Department: 3671)
Hydraulic and earth engineering
Drainage or irrigation
C073S073000, C324S690000
Reexamination Certificate
active
06719488
ABSTRACT:
TECHNICAL FIELD
This invention relates to the technology of measuring the water content of the soil, as well as a method of cultivation and an apparatus for cultivation that use the technology. The invention relates particularly to a method that measures the water content of the soil and performs pF conversion to determine its pF value in order to facilitate soil management and enable the saving of water, resources and labor, as well as a method and an apparatus for irrigation control which control the supply of water or nutrient (nutrient solution) to the soil on the basis of the measured pF value. The term “soil” as used herein refers to all materials that support the underground parts of plants such as root and subterranean stem; the term includes not only what is commonly called “soil” but also solid mediums such as sand particles, gravel stones, smoked coal and pumice.
BACKGROUND ART
In their cultivation on the soil, the growth of field crops is largely dependent on the soil-moisture content which can be controlled in various ways; in lands of high moisture content, enhanced drainage is performed whereas in lands of low moisture content, irrigation is performed, which is enhanced in dry seasons. In order to ensure a favorable growth of field crops, the accurate moisture content in the soil must be known.
High-grade vegetables such as corn salad and tomato are usually grown in crop fields but sometimes they need to be cultivated in open-area facilities and greenhouses with the environment being precisely controlled as in industrial plants. This cultivation method is called “protected cultivation”. Cultivation in crop fields involves supplying fertilizers and other nutrient sources to the soil while applying water to the crop. In protected cultivation, solution culture is preferably adopted, according to which sand particles, gravel stones, smoked coal, etc. are laid down to make mediums which are supplied with aqueous nutrient solutions by irrigation. However, optimum irrigation has not always been achieved in the actual cultivation, particularly in solution culture.
Solution culture can be classified into three types, hydroponics, aeroponic and solid-medium culture. In solid-medium culture, continuous drip irrigation is commonly adopted. In continuous drip irrigation, timer or otherwise controlled automatic irrigation is the dominant approach but optimum irrigation is not always assured. This is because the amount in which the nutrient solution is absorbed by crops being cultured is dependent on various factors including the amount of solar radiation, as well as the temperature and humidity in the greenhouse. For example, the transpiration from crops being cultivated is very high if the amount of solar radiation is large and the greenhouse has high temperature and low humidity. On the other hand, the transpiration from crops being cultivated decreases on a rainy day. The absorption of nutrients by crops being cultivated is also largely dependent on the process of their growth and if they have grown up, the absorption of nutrients becomes very high. It is known that high-quality fruits with high sugar content can be obtained by reducing the water supply after they have grown to a certain extent. However, timer and otherwise controlled automatic irrigation is incapable of meeting those environmental conditions for cultivated crops at various stages of their growth unless the number of irrigations, the start time of irrigation and the duration of irrigation are daily set for new values.
This is not “timer or otherwise controlled automatic irrigation” in the true sense of the term and it is highly doubtful whether optimum irrigation can really be achieved. For these reasons, timer or otherwise controlled automatic irrigation often involves over-irrigation in order to prevent wilting or other troubles of crops but then it has been impossible to avoid root rot due to over-irrigation and increased drainage (i.e., increased quantities of nutrient solution and water are discarded).
Speaking of the relationship between the moisture content of the soil and field crops, not all of the water in the soil is available to field crops and bound water in the soil is not available to the growth of field crops. The moisture content of the soil also varies with weather changes; the soil is filled with water if there is a heavy rain but thereafter the water is gradually absorbed by the lower soil layers and the moisture content of the soil decreases. The soil filled with water is equivalent to what occurs in hydroponics and its air permeability is too low to be suitable for open-field cultivation. If, at the subsequent stage, the moisture content of the soil decreases considerably to a level below a certain threshold, the root is no longer capable of sucking up water and the capillary network in the root is interrupted, causing the root to wither. Once this stage has been reached, the root will no longer recover from withering even if it is supplied with water; therefore it is necessary that the moisture content of the soil be kept higher than the lower limit defined by that stage.
Since the wetness of the soil is determined by the potential of water in the soil, it is held inappropriate that the wetness of the soil which is related to the cultivation of field crops should be simply expressed by the moisture content of the soil. A more preferred method is by expressing the wetness of the soil on the basis of its water potential.
One of the factors that describe the wetness of the soil is the “pF value”. Being first proposed by R. K. Schofield in 1935, the pF value is an index for the matrix potential as a soil-water potential. The matrix potential is a drop in chemical potential resulting from the interactions between water and soil particles, as exemplified by capillary, intermolecular and Coulomb forces. Stated briefly, the matrix potential is the force by which water molecules are attracted to soil particles. The common logarithm of the absolute value of a matrix potential expressed by a graduation on a water column (cm) is called the pF value. The soil-water potential &phgr; expressed by a graduation on a water column (cm) and the pF value are related by pF=log(−10.2 &phgr;).
The pF value is a quantity that describes the quality of water in the soil (which is a nutrient in solution culture). A near-zero pF value represents the state of the soil that is filled with water. The moisture that remains in the soil 24 hours after rainfall or irrigation is called field capacity and has a pF value of about 1.7; the water which is present in the range from the field capacity to the primary wiltig point (pF of 3.8) at which a crop starts to wither is called “available water”. In practice, however, the growth of crops begins to experience troubles at a point where more water exists than at the primary wiltig point. The point is where the capillary network in a crop's root is interrupted to stop the movement of water from the root. Called the rupture of capillary network, this point has a pF of about 2.7. Hence, for cultivation of crops, it is generally held that the pF value is suitably within the range from 1.7 to 2.7. For these reasons, the moisture present in the pF range of 1.7-2.7 is called “easily available water” and for cultivation of field crops in the soil, it is required to maintain this easily available water in the pF range of 1.7-2.7. The descriptions of the pF value and the soil-water potential may be found in “Dojo Kankyo Bunsekiho (Analyses of Soil Environment)”, ed. by the Editors' Committee on Analyses of Soil Environment under the supervision of the Society of Soil and Fertilizers of Japan, published by Hakuyusha, first printing in 1997, pp. 48-51; “Tsuchi no Kankyoken (Environment of Soil)”, ed. under the supervision of Shingo Iwata, published by Fuji-Techno System, 1997, pp. 72-76; “Dojo Shindan no Hoho to Katsuyo (Soil Analysis—Methods and Applications)”, Shunrokuro Fujiwara et al., published by Nosangyoson Bunka Kyokai, Corporation, 1996, pp. 72-77; and
Kamiya Ichiro
Kuroda Tetsuo
Narasaki Yuzo
Otsuka Hidemitsu
Ebara Corporation
Mayo Tara L.
Pezzuto Robert E.
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