Water use of Pinus radiata D. Don on bare ground at the Lincoln agroforestry experiment, Canterbury, New Zealand

Abstract

This study evaluated the rainfall distribution and the soil water storage at different positions of Clone 3 and Seedling trees of Pinus radiata genotypes grown in bare ground during early summer (September 14 to 30 November) 1994. The predawn and mid-day plant water potential of two genotypes was also evaluated. Soil water storage was monitored weekly using Time-domain Refletometry (TDR) Model 3333 and Neutron Moisture Meter (NMM) Model Troxler 4300 and the plant water potential measured by Pressure bomb. The daily rainfall was collected using plastic cups and measured by graduated cylinder immediately after any rainfall occurred.

Rainfall interception by Clone 3 and Seedling trees was not significantly different from each other; however, seedlings intercepted 3.4% more rainfall than Clone 3 trees. The highest rainfall receipts were at 0.9m on the south side of the trees. A rain shadow occurred at 0.9m on the north side of the trees where less rainfall was intercepted by the trees. Seedlings had 14.9% higher total soil water storage than Clone 3 trees did, and most water was held in the 0 to 20cm depth.

There was no significant difference in water use between genotypes. Cumulative ET was highest in the 0 to 20cm depth in all positions. Water use averaged about 7mm week⁻¹ for this slice of soil. The plant water potential of Clone 3 and Seedling trees was affected by soil water content. The predawn plant water potential of Clone 3 trees was 2.9% higher than Seedling at the start of measurement (September 14). Higher predawn and mid-day plant water potential was in Clone 3 trees where more stress was occurred. The highest moisture stress in both genotypes occurred on November 29 when soil water storage was less. There were slight differences in shoot growth. Seedling trees shoots were 1.6% greater in diameter and 4.7% longer than in Clone 3 trees.