EXPLORATION AND EXPLOITATION OF SOIL BY APPLE, KIWIFRUIT, PEACH, ASIAN PEAR AND GRAPE ROOTS

Measurements of root-length density (RLD) in a range of 31 apple, kiwi fruit, peach, Asian pear and grape orchards were used to derive indice s to describe the exploration and exploitation of rooting volumes. Orc hards were of various ages and located on a range of soil types, geogr aphic regions, management systems etc. Data were obtained from core sa mples of volume 1.66 x 10(-4) m(3) randomly taken within a ''standard volume'', determined by average planting grids, of 2 m radius centred on tree stems, and 1 m depth. Root systems were described using an exp loitation index, E(phi), and an exploration index, E(0). E(phi) is def ined as the proportion of the soil volume which contains roots at RLD greater than or equal to some specified value, phi. E(0) is defined as the proportion of the soil volume which contains roots at any RLD gre ater than zero. These indices are dependent on sample size, as are all volumetric or soil-coring data. Estimates of E(0) for each orchard we re obtained as the proportions of cores containing any RLD>O and asses sed for dependence on species. Peach trees had a significantly higher value of E(0), equal to almost 1.0, compared to the other four species where E(0) was approximately 0.8 (p less than or equal to 0.01) or le ss. There was also some variation with age. E(0) was lower for very yo ung plants which had not fully occupied the sampled soil volume. Explo ration indices for woody roots increased with rootstock age but otherw ise did not explain large differences in E(phi) between species for gi ven phi values. For example at phi = 0.05 x 10(4) m.m(-3), E(phi) was approximately 0.45 for peach and kiwifruit, and 0.05 for apple, Asian pear and grape, whereas at phi = 0.5 x 10(4) m.m(-3) the corresponding values were 0.1 and almost zero. Negative exponential curves relating E(phi), scaled by dividing by E(0), to phi were fitted for each of th e 31 orchards. Exponents for these curves, k, were significantly small er for kiwifruit and peaches than apples, grapes and Asian pears (p le ss than or equal to 0.05), and smaller for apples than grapes and Asia n pears (p less than or equal to 0.05). A larger k implies a rapid fal l-off in E(phi) as phi increases. Although all five species contained zero and low RLD samples, only kiwifruit and peaches contained higher RLD values and consequently have higher mean RLD. This trend was consi stent across all soils, regions, sampling dates, and plant ages. The a nalyses demonstrate that core sampling can give useful insights into m acro-scale root-system distribution, such as the proportion of a soil volume explored and how it is exploited. If positions of core samples are noted during sampling using angular direction, depth and radial di stance as spatial coordinates the method can be used to describe root- system structures.