Effect of undercutting and wrenching on growth of Pinus radiata D. Don seedlings.
cf. FA 31 No. 601.] Seedlings of P. radiata, from autumn sowings at Rotorua, New Zealand, were undercut in Dec. and then wrenched weekly (W/1), fortnightly (W/2), monthly (W/4), or not at all (W/0), and their growth was studied at intervals of 2 weeks for 3 months. The three treatments significantly reduced height growth and leaf and stem growth. The relative growth rate (RGR) of W/0 seedlings was significantly greater than that of wrenched seedlings. RGR was not affected by frequency of wrenching. Rates of root growth were similar for all four treatments but the root systems were more compact and fibrous in treated seedlings. W/1 and W/2 seedlings had similar root/shoot ratios throughout the experimental period. The ratio was significantly lower for W/4 stock, and in W/0 stock it was significantly lower than in W/4. Net assimilation rates (NAR) and leaf weight ratios of W/0 seedlings were significantly greater than those of wrenched seedlings. Undercutting and wrenching greatly increased the proportion of total C14 photosynthate translocated to the roots. The wrenched seedlings had a smaller proportion of starch and sugars in the stem. Contents of both reducing and total soluble sugars were significantly higher in W/4 seedlings than in the others, and root starch content was also greater. The general effect of undercutting and wrenching was thus to produce planting stock with little soft, new shoot growth, a high root/shoot ratio, and a compact mass of fibrous roots. Trials with W/0 and W/2 seedlings only were made in March and May. Seedlings tended to show the same responses as in the summer (Dec.) trial in terms of movement of C14-assimilate to the roots but the response was less than in Dec. KEYWORDS: Nurseries \ nursery practice root pruning, undercutting \ Nurseries \ nursery practice wrenching \ Pinus radiata nursery practice