Final answer:
The statement regarding the leaching fraction being less than the leaching requirement for a field with nonuniform compensated irrigation is true. Proper irrigation management that compensates for nonuniformity results in efficient water use and reduces excess water for leaching, thus decreasing the leaching fraction relative to the leaching requirement.
Step-by-step explanation:
The statement that for a field with no under irrigation, in which the irrigation duration compensates for nonuniformity, the Leaching Fraction is much less than the Leaching Requirement is likely True. Leaching Fraction refers to the portion of the irrigation water that passes through the root zone, intended to prevent the buildup of salts in the root zone by leaching them out. The Leaching Requirement, on the other hand, is the amount of excess water needed to keep the salt content of the soil at a level that will not harm crops.
Irrigation practices aim to ensure adequate soil moisture for optimal plant growth without excessive watering that contributes to inefficient use of water and potential leaching of nutrients and salts beyond the root zone. When irrigation is carefully managed to counter nonuniformity, the resultant effective use of water means that the actual need for leaching to alleviate salinity buildup (Leaching Fraction) will be less.
Nonuniform irrigation can lead to uneven distribution of water and can cause areas within a field to receive too much water, potentially leading to unnecessary leaching of nutrients and waterlogging. However, if irrigation is done such that it compensates for these nonuniformities, the water is used more efficiently, and as a result, the Leaching Fraction would indeed be less than what theoretically might be required, or the Leaching Requirement, to maintain soil salinity at levels acceptable for crop health.