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Saturday, March 17, 2018


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Search results on 03/17/18

4585. Morrow, L.. 1990. Meaningful relationships.. Growers Guide, May 1990 A6.
Calcium is an important nutrient to consider. It gives strength to plant cell walls, making them more resistant to disease. It also interacts with nitrogen and helps the latter enter the plant through the leaves when foliar fed. It also reduces N volatility. Foliar applications of N have been shown to be twice as effective as soil applications. Calcium by itself is best applied at seeding time.

5735. Rasmussen, P.E. and C.R. Rohde. 1988. Stubble burning effects on winter wheat yield and N utilization under semiarid conditions.. Agronomy J. 80:940-942.
Burning vs. not burning was examined at 3 nitrogen levels over 6 years (3 crops). Burning had no effect on grain yield or grain N uptake. Burning increased straw yield when wheat was fertilized by N, but had no effect on straw N uptake. Burning did not decrease foot rot incidence or severity, but did reduce downy brome density. T: Effects of stubble burning and N fertilization on grain and straw of winter wheat 1980-85. Effect of stubble burning on foot rot infection. Effect of stubble burning on downybrome infestation.

7524. White, J.G.H.. undated. Grain legumes in sustainable cropping systems; a review.. unpublished manuscript, Plant Science Dept..
This paper briefly reviews the role that grain legumes can play in sustaining cropping systems. It presents various estimates of N fixation of grain legumes, with lupin and fababean showing the highest rates, followed by peas and lentils, chickpeas, and soybeans. Phaseolus beans are generally poor N fixers. Fababeans are more tolerant of soil mineral N than other species and will still fix large quantities of N when mineral N is present. Under drought stressed conditions, peas and lentils were more efficient in N fixation than fababeans. Only in lupins and fababeans was N fixation normally greater than the N removed in the seed. The roots and nodules of grain legumes are likely to be the greatest source of N for following crops. This N is often quickly mineralized within several weeks after harvest, and strategies are needed to prevent its loss. Grain legumes are also beneficial break crops, particularly for soil-borne diseases, and can help to control certain grassy weeds. Preceding grain legumes with a brassica crop has reduced the incidence of Aphanomyces root rot in peas, due to sulfur containing compounds. Most grain legumes suffer reduced yields if soils are compacted and poorly aerated. The paper contains numerous references and tables on nitrogen relations.

8783. Marschner, H.. 1986. Relationship between mineral nutrition and plant diseases and pests. Chpt. 11. p. 369-390.. IN: Mineral Nutrition of Higher Plants. Academci Press, Orlando. 674 pp..
Although plant resistance to diseases is genetically controlled, it is considerably influenced by environmental factors, including level of plant nutrition from the soil. Excees N appears to lower disease resistance while potassium sufficiency increases resistance. Calcium makes cell walls more resitant to fungal parasite attack. Deficiencies of nutrients which lead to an accumulation of low molecular weight organic substances lower plant resistance. Boron-deficient wheat has a higher infection with powdery mildew. The severity of take-all on wheat is greatly inhibited by lower soil pH, beginning at 6.8. Ammonium-based fertilizers which acidify the rhizosphere can inhibit take-all severity, while nitrate N increases pH and disease problems. Ammonia is toxic to certain Fusarium species and nitrite is toxic to Pythium and Phytophthora. There is often a positive correlation between nitrogen application and pest attack, as young or rapidly growing plants are more susceptible. A large potassium supply often decreases pest attack. If a fertilizer increases the content of soluble organic nitrogen in plants, sucking insects tend to become more of a problem. The physical surface of leaves can be made less attractive to insects by some foliar sprays containing sodium silicate. One experiment with wheat found that without chemcial disease control, rust infection reduced grain yield in all fertilizer N treatments, but the zero N plots yielded the greatest. With fungicide, split N application led to highest yields.

11095. Smiley, R.W. and R.J. Cook. 1973. Relationship between take-all of wheat and rhizosphere pH in soils fertilized with ammonium vs. nitrate nitrogen.. Phytopathology 63:882-890.
Take-all of wheat was reduced by ammonium fertilizer supplemented with N-Serve to slow nitrification, but was severe with no added N, or with calcium nitrate at N rates equivalent to that supplied by ammonium. The addition of lime negated the control of ammonium. A good correlation existed between rhizosphere pH and disease severity, but not with bulk soil pH. The rhizosphere pH dropped with ammonium uptake, increased with nitrate uptake, and remained unchanged with no added N. Disease severity was progressively less as rhizosphere pH dropped below 7, and was greatly reduced below 6.6. In a fumigated soil, disease was controlled only when pH was below 5. Reduced disease severity apparently resulted from direct inhibition of the pathogen at pH less than 5 and indirect inhibition (possibly a biocontrol) above 5.

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