There is an optimum moisture content for every crop, but this ideal level often varies throughout the season. Vines, for example, require a high moisture content during flowering and fruit set, but towards the end of the season lower moisture contents will give a higher sugar content and better quality grapes. The grower needs to know what the optimum moisture content for his particular crop is and how this varies throughout the season. Measuring Soil Moisture Content Soil moisture measurement is the key to successful irrigation. There are many different ways of doing this, but it is critical to understand what is actually being measured.
All measurement systems have a sphere of influence and a response time.
Plants are constantly taking water from the soil, giving moisture gradients. There is therefore no one value of soil moisture. There is a profile of soil moisture values extending outwards and downwards from the root zone. In addition, soil moisture can vary quite rapidly with time. Instruments such as neutron probes and capacitance-based systems will average soil moisture measurements over a wide area because they have a large sphere of influence.