Additional effects of fertilizing on several foliar nutrient concentrations and ratios inEucalyptus grandis
The interaction responses to N, P, K fertilizing and limimg in four experiments withEucalyptus grandis are described. Inclusion of the N—P and P—K relationships gives a clearer understanding of the nutrient requirements of this species. Phosphorus and nitrogen supply is of great importance, but must be well balanced when either or both are adequately supplied in specific circumstances. Potash supply is also of importance, especially in conjunction with phosphorus, although no direct benefit has been found in these experiments. Increased soil pH reduces the uptake of these latter two nutrients. Magnesium is of greater importance and more readily taken up than calcium inE. grandis. Zinc seems to be the most important of the micro-nutrients and its interactions make it evident that Zn-enriched fertilizers should be used. Manganese levels are generally high where growing conditions are adverse. The great importance is indicated of the foliar N/P and P/K ratios as diagnostic criteria for evaluating fertilizer needs inE. grandis.
Fertilisation in South African Forestry
SYNOPSIS The history of forestry fertiliser research in Southern Africa is described briefly. Fertiliser investigations in wattle started in the 1920s and in pines in the 1930s, but investigations with eucalypts started only in the 1950s. Nevertheless, it is noted that today more is known about the nutritional requirements of eucalypts than of the other species, mainly owing to the application of foliar analysis in combination with suitable experimental designs. The importance of the various nutrients for the different species is discussed with reference to experiments undertaken in Southern Africa. The controversial issue whether gains from fertilising are maintained is examined and the conclusion is reached that unsatisfactory design and insufficient replication are the main causes that initial responses have not been shown to be maintained. An indication of the commercial use of fertiliser in wattle, eucalypt and pine growing is given and the high profitability of fertilisation for these species indica...
Differential susceptibility of two populations of Eucalyptus viminalis labill. to iron chlorosis
SummaryIn comparing two populations of E. viminalis observations indicated that plants of a calcareous population (i) showed a greater yield at high pH, and when subjected to Fe-stress, (ii) took longer to develop chlorosis, (iii) more quickly developed new roots, and (iv) were capable of removing more Fe from solution than were plants of an acid population. Some Fe-stressed plants also appeared to be able to reduce Fe3+ to Fe2+, but population differences have not yet been clearly established. Plants from an acidic population accumulated very high levels of P in leaves when grown in alkaline solutions and, consequently, exhibited high P/Fe ratios, chlorosis, and symptoms of P toxicity.