Penetration resistance showed a similar trend to bulk density with increasing water content (Figure 2). However, clear differences were observed among the soils. Piarco showed a notably lower response to water content compared to the other soils, whilst Chagaramus which had low bulk densitys showed penetration resistance values similar to and even greater than some clay soils. The difference in response of Piarco soil to compaction and soil strength as measured by bulk density and penetration resistance respectively supports statements made by [29] that either parameter alone cannot be used to assess changes in the soil fabric
due to compaction. Peak penetration resistance and corresponding CMC increased with increasing clay content (Table 2). Values ranged from 2.4 - 8.2 MPa and were generally in the range reported by [2]. Princes Town showed an unusually low value, considering that it is a cohesive soil. The preponderance of smectitic mineral in Princes Town [23] seemingly influenced penetration resistance, through the large water holding capacity. Although the Chagaramus peaty clay has not been mineralogically characterized, its parent material originates from the Northern Range, alluding to a dominance of 1:1 clay minerals. The influence of mineralogy on penetration resistance as assessed via the cone index requires further investigation. Reference [30] stated that organic matter increases soil strength and reduces the effects of compaction. This was evident in Chagaramus, which showed the 3rd highest peak penetration resistance . A strong relationship exists among organic matter content, applied stress and soil strength. Reported peak penetration resistance values were mostly greater than the ranges reported in the literature for limiting root growth [31]. Additionally, these peak values occurred below the plastic limit, at moisture contents typically experienced during crop cultivation. An appropriate moisture content to prevent physical limitations should be between the critical moisture contents for bulk density and penetration resistance.