**6. Irrigation scheduling**

There are variations in water requirements by plants at different growth stages; hence a need for irrigation scheduling that could supply optimum water required by plants at the appropriate time. Irrigation scheduling considers when and how much water should be applied to plants [23, 24]. These could be predetermined by monitoring the soil water status and the crop water requirements. Soil moisture-based, evaporation-based, and plant-based measurements are the most common methods for scheduling irrigation to aid effective use of water and promote crop productivity.

Soil moisture content can be used to determine an irrigation schedule. The moisture content of the soil is measured with the aid of instruments, these include FDR soil moisture meter (DIK-321A, Daiki Rika Kogyo Co. Ltd., Kounosu, Japan) [25, 26] *Fundamentals of Irrigation Methods and Their Impact on Crop Production DOI: http://dx.doi.org/10.5772/intechopen.105501*

and when soil moisture goes below a critical level, irrigation commences. The soil moisture-based irrigation schedule takes into consideration the type of soil and its composition to determine the availability of water in the soil. Sandy, loam, and clay have a low, medium, and high availability of water, respectively.

The evapotranspiration schedule takes into consideration soil evaporation and plants transpiration rates. The amount of water required by a plant is determined by balancing the amount of water input into the soil and the amount of water loss. Evapotranspiration data allow us to better understand when to irrigate an actively growing plant.

Also, the plant observation method could be used to determine the irrigation schedule. This method takes into consideration the changes in plant characteristics to determine when to irrigate the plant. There are common morphological symptoms of plants under stress or low water deficit. These visible changes including chlorosis, dried leaves, curling of leaves, and stunted growth were used to assess the timing of irrigation. To determine chlorosis and water stress for irrigation scheduling, a chlorophyll meter (SPAD 502 PLUS, Minolta corporation, Ltd., Japan) and a chlorophyll fluorometer (PAM-2000, Walz Co., Ltd., Effeltrich, Germany) [25] are used.
