Step 1: Understanding the Concept:
Soil water is grouped into three forms by how strongly the soil holds onto it: hygroscopic, gravitational and capillary. The question asks which one is the source a crop actually draws upon for its daily growth.
Step 2: Key Formula or Approach:
A rough working scale of soil moisture tension helps here. Hygroscopic water is held at very high tension, far beyond what a root can pull against. Gravitational water is held at almost no tension and drains out under its own weight. Capillary water sits at a moderate tension, low enough for roots to pull it out, but high enough that it stays in the root zone instead of draining away.
Step 3: Detailed Explanation:
Right after rain or irrigation, the gravitational water in the large pores drains downward within one to two days and moves below the root zone, so a crop gets only limited benefit from it.
The hygroscopic water forms a very thin film stuck to the particle surface, and even at wilting point this water is still present in the soil, unused, because roots cannot generate enough suction to remove it.
Once the gravitational water has drained away, what remains in the smaller pores is capillary water, held by surface tension against gravity but still weak enough that plant roots can pull it in day after day. This is why capillary water is treated as the usable, plant-available water in soil.
Step 4: Final Answer:
Capillary water is the type of soil water available for normal crop growth, so option (3) is correct.