"hard soils" is correct and usable in written English
You could use it to describe a type of soil that is difficult to till or an area with particularly dense or compacted soils. For example: "The farmer struggled to till the hard soils in the rocky hillside."
The level of shaking for a large earthquake would be weakest in areas with rocks or hard soils, and strongest on the soft soils.
The appropriate furrow opener for the control system was investigated on soft, medium, and hard soils.
The structures were subjected to strong seismic ground motions recorded on soft and hard soils of earthquakes generated at subduction seismic sources.
Results showed that the hoe furrow opener showed no significant difference in furrow shape even in hard soils with great soil penetration, and the variation of the lateral and vertical seed distributions was reasonable.
The importance of root hair traits for P uptake is well established (Lynch 2011; Brown et al. 2012a), and root hairs are also believed to be important for uptake of other nutrients (Drew and Nye 1969; Gahoonia et al. 2006; Samal et al. 2010), for rhizosheath formation, and for penetration of hard soils (Brown et al. 2012b; Haling et al. 2013; Lynch et al. 2014).
Although important advances have been made in this field, the precise mechanisms and specific root traits that enable roots to penetrate into hard soils remain largely unknown.
As for bulbs, it's hard to imagine digging into this hard soil, come fall.
Putting down roots in this ancient, fertile but very hard soil has been a challenge.
One furtively scans his surroundings, while another jams his spade through the hard soil.
The shells were often eroded, but never distorted like tree roots that grow in hard soil.
In the park itself, skyscrapers now cast shadows on the hard soil.
