,,
Substrates and Root Zone Dynamics
Some manufactured hydroponic substrates such as stonewool slabs or blocks , and even some coco fiber products , can have physical properties specifically designed for certain crops . Stonewool slabs have differences not only in overall moisture and air-filled porosity levels , but also carefully calculated moisture gradients between the top and base of the slab . Many of these specialized products are aimed at different crops , growing climates and uses , and help provide the optimum levels of moisture in the root zone . Growing conditions also play a role in root zone moisture dynamics . The rate of transpiration , temperature , and humidity should be taken into account when choosing a substrate . Crops growing under warm , high-light , low-humidity conditions requires frequent irrigation and benefit from a moisture retentive medium that helps prevent drying out of the root zone and gives more of a safety buffer should failures with pumps or the power supply occur . Under cool conditions with slower growth and small plants , substrates that are free-draining and retain lower levels of moisture assist with prevention of oversaturation . These types of free-draining open substrates are also more forgiving of the application of high levels of nutrient solution that may be needed for plant nutrition , but at the same time not contributing to a water-soaked root zone when growth and transpiration rates are low .
Tomato fruit splitting can have a number of causes , though large moisture fluctuations in the root zone are a common cause .
The difference between the wet and dry weight
IS THE WATER HOLDING CAPACITY OF THAT SUBSTRATE .”
Root Zone Dynamics and Oversaturation
When nutrient solution is irrigated onto a substrate it displaces air in the open pores of the material . When draining subsequently occurs , more air is drawn down into the root zone . If overirrigation is occurring , the air-filled pores remain saturated for too long and the plant has less access to the oxygen contained in the air . Oxygen is essential for root system respiration and healthy functioning and considerably more O 2 is present in air than can be dissolved into the nutrient solution . Plants exhibit a strategy termed ‘ oxytropism ’ where roots will avoid growing into oxygen-deprived areas such as overwatered hydroponic substrates and stagnant nutrient solutions . This is most often seen inside the base of growing containers or slabs of substrate as areas devoid of any root growth or in small , thin , brownish roots that have died back due to suffocation and oversaturation . Other symptoms of an overly wet substrate and water logging are chlorosis ( yellowing ) of the new foliage , older leaves may yellow and fall from the plant , flower and fruitlet drop are also common as are outbreaks of root rot pathogens such as Pythium . Another symptom of extreme overwatering is epinasty , where excess moisture in the root zone causes ethylene gas to build up in the plant resulting in severe bending downwards of the leaves . This is often mistaken for wilting , however , growers should always check to determine if any wilting is actually due to an overly dry root zone or epinasty because of water logging .
Strawberries are a crop that has little tolerance for oversaturated root zones .
Checking that the root system is healthy and spreading through the substrate is a good idea .
24 Maximum Yield