Rain need by maize in Kenya

Crop water balance model

Maize water requirement during the growing period is calculated by Kc * ET0, per FAO's method.

Kc is the crop coefficient, unitless. It changes with crop varieties and physiology stages.  FAO divides a growing cycle into four stages, Kc is highest in the third stage which means the crop needs the highest amount of water. There is a lookup table  to find Kc for different maize varieties in different stages http://www.fao.org/3/X0490E/x0490e0b.htm#chapter%206%20%20%20etc%20%20%20single%20crop%20coefficient%20(kc)
 
 
ET0 is the Reference ET, mm/day. It can be estimated by different methods via temperature, humidity, solar radiation, etc but it's quite complex. Daily ET0 can also be downloaded from Wapor (https://wapor.apps.fao.org/catalog/WAPOR_2/1/L1_RET_E). 



Predicted rainfall received in 2022 long rain when planting on different dates

In order to help farmers to choose an appropriate planting date, we estimated the rainfall received in 2022 long rain season if choosing different planting date by calculating the average of historial analog years. For a 120-day maize the results are shown below. Different colors represent 10 counties in Kenya. X-axis is the planting date ranging from March 1st to May 31st. Y-axis is the rainfall received during a growth period of 120 days. In most counties, the later you plant, the fewer rainfall you will receive. The constant horizontal yellow line is the water requirement of 120-day maize.

Furthermore, we break down the total rainfall received to rainfall received in each of 4 maize growth stages. Different colors represent 10 counties in Kenya. X-axis is the planting date ranging from March 1st to May 31st. Y-axis is the rainfall received during a particular growing stage. The constant horizontal yellow line is the water requirement of 120-day maize.

A good way to use the above diagrams is to see how predicted rainfall received in the growing season will change with planting date and compare that with maize water requirement in order to decide a planting date. Please bear in mind that not all rainfall received can be used by maize. The percent of effective rainfall can be as low as 50% or lower.

A superset dashboard has been established for easy view (that link might not work, we are trying to make it public)http://superset.plantvillage.psu.edu/r/36

 

http://superset.plantvillage.psu.edu/r/36

 




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