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.
The effects of fertilizing on the foliar nutrient concentrations inEucalyptus grandis
The foliar concentrations of macro- and micro-nutrients were studied in four N P K-lime fertilizer experiments withEucalyptus grandis, in the Natal Midlands and Zululand, South Africa. The sampling method and the chemical analysis of the foliar nutrient concentrations are described. Nutrient levels are similar to results found elsewhere and they differ little from those for other eucalypt species. There are many significant changes in foliar nutrient concentrations as a result of fertilizing. The relationship between soil and foliar N and P concentrations are clear as well as the importance of well-balanced N/P and Ca/Mg ratios. The Zn-P and Zn-Mg relationships make it apparent that Zn-enriched fertilizers should be used forE. grandis.
Effect of Soybean Cyst Nematode (Heterodera glycines) on Yield of Resistant and Susceptible Soybean Cultivars Grown in Ohio.
Soybean (Glycine max) producers in Ohio rarely use soybean cyst nematode (Heterodera glycines, SCN)-resistant cultivars because of concerns over limited yield potential and lack of resistance to Phytophthora sojae. A two-year study was initiated to determine grain yield and nematode population increase on soybean cyst nematode-resistant cultivars in maturity groups II and III in production fields. Sites differed in soil texture, nematode densities, and P. sojae infestation at a number of locations in Ohio. Soil was assayed for nematode densities before planting and at harvest. Yields of resistant cultivars averaged 0% to 18% higher than those of susceptible cultivars in fine-textured soils with average preplant populations ranging from 463 to 14,330 SCN eggs/100 cm(3) soil. In coarse-textured soils, yields of susceptible cultivars were 21% to 56% less than the resistant cultivars with average preplant densities ranging from 1,661 to 15,558 SCN eggs/100 cm(3) soil. The reproductive index ranged from 0.1 to 5.5 for resistant cultivars and 0.4 to 112 for susceptible cultivars. In 1993, yield of P. sojae-susceptible, nematode-resistant 'Asgrow A 3431' was as high as yield of the P. sojae-resistant, nematode-susceptible cultivar 'Resnik' in a Phytophthora-infested field. The nematode-resistant cultivars Madison Experimental 131527 and Asgrow A3431 had higher yields than AgVenture AV1341 and susceptible cultivars Resnik and Kenwood when compared over five nematode-infested sites. Nematode-resistant cultivars were found to be excellent alternatives to currently grown susceptible cultivars for managing SCN where group III cultivars are used. However, better cultivar alternatives may be needed for sites with combined Phytophthora root rot and cyst nematode problems.