Calculating the available water capacity for the plant an agricultural producer possesss a property with alone data. Which information it needs to know the amount of available water for the plant? How it calculates this amount? Ahead of this situation, the producer must have in hands four information, is they: 1) Water percentage in the field capacity (- 33 kPa); 2) Water percentage in the point of permanent withering (- 1500 kPa); 3) Density of the ground (g/cm3); 4) Thickness of the ground layer that the density of the ground represents (of where it was removed) (in centimeters). To get these information, the producer must collect a ground sample deformed and not send it some agronmico institute next to its property. In this place, it must request the technician so that they carry through the measure of density of the ground, as well as supplies the curve of retention of the water in the ground. This last one, will contain the amount of water in the ground in the capacity of field and the point of permanent withering. Of ownership 20 cm and 20 40 cm and to get 40 and 60 mm of water, respectively, we can say that if the culture that we will plant possesss roots up to 40 cm of depth of the ground, then has available water 100 mm for the plant. Knowing it amount of water that the culture uses (technical the evapotranspirao), it can be known will be had or water enough plant not to grow it and even though to foresee will have sazonais problems of water scarcity, called technical of hdrico deficit, needing then irrigation.>