Stressmeter

An apparatus for determining a critical level of soil humidity for plants comprising:

• an external body;
• a soil recipient container means hermetically sealed to said external body, said soil recipient container means for receiving a soil therein, said soil recipient container means having a collecting pipe thereon for passing water into the soil, said collecting pipe having an interior passage;
• a well positioned within said external body, said well containing water therein;
• a pressure cell means connected to said well to controllably pass water from said well to said soil recipient container means, said pressure cell means having an established resistance to the passage of water, said pressure cell means being positioned within said external body away from said interior passage of said collecting pipe, said pressure cell means being permanently under the water in said well at a constant level, said pressure cell means for forming a meniscus having a pre-established strength for resisting water movement toward the soil;
• and
• an air admitting pipe means in sealed relationship with said external body, said air admitting pipe means having an end opening exterior of said external body to allow air to pass into said air admitting pipe means, said air admitting pipe means communicating with said pressure cell means, said air admitting pipe means for transmitting air into said pressure cell means when energy in the soil recipient container means is higher than the resistance of said pressure cell means, said pressure cell means for urging water from the well into said interior passage of said collecting pipe.