Subsoil conditions and maximum rooting depths of commercial pea crops grown in Canterbury, New Zealand

Abstract

In order to use the water balance approach to schedule irrigation, estimates of crop maximum rooting depths (Z_max) are needed. Published guidelines for irrigation scheduling have suggested that Z_max for peas can be taken as 80 cm. The objectives of this research were firstly to ascertain how accurate the 80 cm estimate of Z_max was for a number of commercial pea crops in Canterbury, and secondly to identify the factors most likely to have limited Z_max for these crops. Values of Z_max for process pea crops at harvest were estimated at ten Canterbury sites during the 1983 – 84 growing season. Soil texture, pH, and dry bulk density were also recorded along with a root disease index, plant population, shoot dry matter, and pea yield. Z_max values for the different sites varied between 40 and 75 cm, with few values exceeding 60 cm. Root penetration to depth did not appear to be much affected by root diseases or subsoil acidity. Rather, subsoil compaction seemed to be responsible for the poor root penetration at many sites, especially where subsoil textures were silt loam or fine sandy loam. There were no clear, simple relations between pea yield or shoot dry matter and Z_max, disease index, or soil dry bulk density. It is concluded that no single value of Z_max should be' recommended for irrigation scheduling purposes, rather Z_max needs to be determined separately for each site in this area.

Keywords:

• irrigation
• peas
• Pisum sativum
• root growth
• plant diseases
• soil compaction
• pH
• soil water balance