Soil strength is an important quality of agricultural soils prone to traffic. Surface hardness (SH) measured by the clegg impact tester (CIT) was evaluated as an indicator for assessing soil strength. Proctor tests were performed on a diverse range of soils to examine the relationships between bulk density (BD), penetration resistance (PR), SH and water content. All three indices showed typical response curves with increasing water content, with notable differences among the soils. Maximum dry bulk density (MDBD), peak penetration resistance (PPR) and peak surface hardness (PSH) showed values of 1.98 Mg·m −3 , 8.2 MPa and 248 Cmax for Piarco, River Estate and Piarco respectively. Corresponding critical moisture contents (CMC) were much greater for MDBD compared to PPR and PSH. SH showed a significant positive correlation with PR, but not BD. Further divulgence into the relationships between SH and other soil properties as well as crop response will facilitate greater use of the CIT.

Abstract:The root zone physical condition influences root development and function, which affects turfgrass growth, quality and performance. The temporal variability of root zone properties was investigated in a factorial experiment combining sand layering compaction and moisture stress on the performance of Savannahgrass (SG) (Axonopus compressus), Bermudagrass (BG) (Cynodon dactylon (L.) Pers.) (cv. Tifway 419) and Zoysiagrass (ZG) (Zoysia spp.) grown in four contrasting soils. Four stresses-drought (D), waterlogging (WL), high compaction (HC) and low compaction (LC)-were applied either with or without a surface sand layer. Root zone properties, including root weight (RW), bulk density (BD), surface hardness (SH), redox potential (E h ) and non-capillary pore space (NCPS), were monitored over a four-month growth period. Surface hardness values were greater for the high compaction effort in treatments without sand, but were highest under drought. Sand addition resulted in lower SH for all grass × soil combinations. The soil texture influenced root zone BD for all turfgrasses, with the clay soils recording significantly lower bulk densities (<1.00 g/cm 3 ) than those with coarser fractions. Compaction had a minimal influence on BD, the effect being further modified by grass type. Low BD was associated with high RW. RW was also significantly higher in the sand-amended treatments. Waterlogging reduced E h for all soils, with higher values recorded in the sand treatments. The redox potential was lowest in River Estate soil and in pots planted with ZG. Across turfgrasses, Princes Town and Talparo soils had significantly lower NCPS for the sand treatment. NCPS was highest for ZG across stress treatments, but values OPEN ACCESSAgronomy 2014, 4 125 were similar to SG under compaction treatments. Sand layering improved the root zone aeration status, particularly with SG, resulting in a better physical condition.

Turfgrass growth, performance and quality are affected by abiotic stress factors and are of primary concern for persons managing turfgrass areas under seasonal tropical climates. Under these conditions, common Savannahgrass (SG) may have a performance advantage over imported hybrid turfgrasses. A greenhouse study was conducted to comparatively evaluate the performance of tropical turfgrasses exposed to water and compaction related stresses across a range of soils, with or without the addition of a surface sand layer. Turfgrass productivity and quality was monitored over a four-month growth period. Clipping yield (CY) was lower at the higher compaction effort for all turfgrasses, but across all stresses, drought (D) and waterlogging (WL) resulted in lower CY. Values were significantly lower under D. SG had the highest clipping yield across all soils. The chlorophyll index (CI) was lower for all turfgrasses under water-induced stress compared to compaction stresses. SG had a significantly higher CI across all stress treatments. Correlation analysis showed a positive (r² = 0.420) and significant (p < 0.05) relationship between CY and CI. Similar to CI, stress type influenced turfgrass visual quality (VQ), with D stress, resulting in the lowest VQ rating among turfgrasses. Bermudagrass (BG) had the lowest VQ across all stress treatments, whilst, comparatively, Zoysiagrass (ZG) had significantly higher VQ under high compaction (HC), low compaction (LC) and WL stress. Overall, SG showed a higher level of tolerance to applied stresses and warrants greater attention as a potential turfgrass under tropical conditions. OPEN ACCESSAgronomy 2014, 4 203

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