Based on the values of the table, the amounts of transpiration to produce 1 ton of dry matters are as follows：
C4 crops： 315t; C3 gramineous crops： 599t
C3 leguminous crops： 694t; Other C3 crops： 570t
If we assume that the land-surface evaporation during the growing period is 0.2 of the amount of evapotranspiration, from Equation (6), the demand for water of the farmland needed to produce 1 ton of dry matter is 25% more than each of the above values.
In view that majority of ferrestrial vegetation are the C3 plants, and assuming the plant community's demand for water is 600t per ton of dry matters, the water resources consumed for each production mentioned above can be estimated as follows. All these water resources are supplied by precipitation on lands.
Potential net primary production： 816,000 (100 million ton/year)
Actual net primary production： 489,600
Yields of foods and timbers： 73,200
Production needed for the yields of foods and lumbers： 122,400
Table 4 shows the water balance of each continent on the Earth. The figures above and in Table 4 suggest that without human activities most of the lands would have been covered by natural vegetation, which would have used about 69% of annual precipitation on earth to produce dry matters. This rate is 10 percentile points greater than the current evapotranspiration rate (58%). For actual net primary production, 41% of precipitation on lands are used, which is about 20 trillion ton less than the estimated amount of evapotranspiration in Table 4. This reflects increases in surface runoff from the bare land areas and in evaporative loss.
According to the data of 1991, approximately 1,870 million ton of grain production required 704 million ha of farmland (including 113 million ha irrigated).
