THE FIELD PEA CROP IN SOUTH WESTERN-AUSTRALIA - PATTERNS OF WATER-USE AND ROOT-GROWTH IN GENOTYPES OF CONTRASTING MORPHOLOGY AND GROWTH HABIT

Root development and seasonal water use of six field pea (Pisum sativum L.) genotypes were studied in a water-limited field environment (Wongan Hills) and in freely watered glasshouse-cultured plants (Perth, WA). From 80-97% of root biomass of the genotypes at peak vegetative growth in the field was located within 20 cm of the soil surface. Roots of one genotype (Wirrega) extended deeper and extracted soil moisture reserves to 2 m, i.e. some 40 cm below that of the other genotypes. Peak evapotranspiration rates (2.7-3.0 mm d(-1)) were attained in the field at or just beyond flowering after which water consumption decreased sharply parallel with increasing moisture stress and declining green area. By contrast, glasshouse-grown plants increased steadily in cumulative transpiration well into fruiting. Judging from cumulative evaporation and dry matter at peak biomass, field crops of the fully leaved genotypes (Dundale, Wirrega and Progreta) showed significantly better water-use efficiency than the three semi-leafless genotypes (Dinkum, L82 and L80). Effectiveness of water usage was also assessed from regressions of dry matter production against cumulative evapotranspiration (field material), gravimetric measures of transpiration loss versus dry matter gain (glasshouse plants) and C-13 isotopic discrimination of shoots of glasshouse-grown plants. All three comparisons showed the tall conventional types (Dundale and Wirrega) to be superior to the four semi-dwarfs. Data are discussed in relation to previous studies of the water-use economy of field pea and other grain crops.