Comparative Evaluation of Common Savannah Grass on a Range of Soils Subjected to Different Stresses II: Root Zone Physical Condition

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 (Eh) 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 Eh 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 ACCESS Agronomy 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.