Search Results - (Author, Cooperation:M. T. Wong)

2013-07-28

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; Caspases/biosynthesis ; Cholera Toxin/immunology ; Disease Models, Animal ; Escherichia coli/immunology ; Escherichia coli Infections/genetics/immunology ; *Immunity, Innate ; Inflammasomes/*immunology ; Lipid A/genetics/*immunology ; Macrophages/*immunology ; Mice ; Mice, Mutant Strains ; Mutation ; Salmonella Infections/immunology ; Salmonella typhimurium/immunology ; Sepsis/immunology ; Toll-Like Receptor 4/*immunology

0301-4622

Criterion equation ; Critical spherical shell ; Enzyme-substrate fast reaction system ; Sink model

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Chemistry and Pharmacology

Physics

Electronic Resource

1573-0867

CERES models ; fluctuations ; lignin ; microbial motility ; mineralization ; nitrate ; nitrate retention ; polyphenol ; synchrony ; water potentials

Springer Online Journal Archives 1860-2000

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Abstract The concentration of native available N in tropical soils fluctuates considerably in response to seasonal changes in soil water potential. Such fluctuation reflects the net effect of inputs of N from mineralization, fertilizers and the atmosphere, and removal by plant uptake, immobilization, leaching and gaseous losses. The greatest concentrations normally occur during the transition between the dry and wet seasons. In East-Africa, up to 184 kg mineral N ha−1 has been measured in the 0–40 cm soil layer and in Trinidad, 143 kg ha−1 was found in the 0–10 cm layer. Release and accumulation of mineral N occur as a result of the influence of soil water potential on microbial activity. This is due to changes in microbial motility, solute diffusion, microbial survival and the release of protected organic matter. A quantitative understanding of these processes should increase the efficiency of use of this valuable N resource by crops. Current methods of forecasting mineralization under field conditions include measurement of the soil mineralization potential, the release of N from seasonal inputs of litter and model predictions. Litter quality is important. Its composition, in particular its nitrogen, lignin and soluble polyphenol content has a major impact on its N mineralization rate. Crop uptake, gaseous and leaching losses decrease the concentration of soil mineral N during the wet season. These losses are important under moist tropical conditions. For example, at Port Harcourt and Ibadan in Nigeria, leaching losses were large in spite of NO 3 - adsorption which decreased the depth of NO 3 - leaching relative to through-flow. To minimise these losses, it is essential to synchronise plant nutrient demand with supply by mineralisation. This is particularly important at the start of the tropical rainy season when high rates of mineralisation often in excess of the relatively low levels of crop demand, are observed. Fertilizer recommendation, the time table for cropping and the farming system used therefore need to take into account the seasonal availability of N. The CERES model simulates crop growth and development and the N-cycle. As development and validation continue, such models should provide a strong basis for better soil, crop and fertilizer management practices. A better understanding of the processes should provide a strong basis for futher development of such models.

Electronic Resource

1573-0867

Leaching ; calcium ; magnesium ; potassium ; nitrate ; tropical soils ; 15N ; urea ; shifting cultivation

Springer Online Journal Archives 1860-2000

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Abstract Calcium hydroxide was applied to monolith lysimeters at Onne in south-east Nigeria. Eight lysimeters were cropped with maize followed by upland rice and four were uncropped. The cropped and two uncropped lysimeters received Mg, K and urea in the first season. Two uncropped lysimeters received no fertilizers. Drainage water was collected during the two growing seasons and analyzed for calcium, magnesium, potassium, sodium, nitrate and chloride. The fertilizer applied in the second season was not leached during the year of application. The cropped lysimeters lost 27 percent of the sum of the exchangeable Ca in the soil profile and the calcium added, and 29 percent of the corresponding sum for Mg. With no crop, the losses increased to 34 and 37 percent, respectively, but with no crop or fertilizer, the losses were similar to those from the cropped lysimeters. The loss of potassium ranged from 6 percent from the unfertilized lysimeters to 10 percent in the cropped lysimeters. The amounts of sodium leached ranged from 29 to 35 kg Na ha−1. The bulk of the calcium and magnesium leached from calcium hydroxide and fertilizers occurred in the second season when the loss was in good agreement with the amount of nitrate lost giving (Ca + Mg)/NO3 charge ratios of approximately one. Urea increased the amount of nitrate leached and led to a corresponding increase in the amounts of calcium and magnesium lost in the drainage water. The charge ratio remained unchanged when the cations were leached only with nitrate derived from the mineralization of soil organic matter. In the cropped lysimeters, this source accounted for about four times more nitrate in the drainage water than the fertilizer.

Electronic Resource

1573-0867

West Africa ; soil fertility ; organic matter ; nutrient dynamics ; water/crop/fertilizer interactions

Springer Online Journal Archives 1860-2000

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Abstract The Alfisols, Oxisols, Ultisols and Inceptisols which dominate the soils of West Africa have sustained crop growth for a very long time. As a consequence, their fertility has become perilously low and the task of increasing or even maintaining the productive capacity of these soils has become perhaps the greatest challenge to agricultural scientists in this latter half of the 20th century. Water is useful not only for the growth of plants but also for the efficient use of costly inputs such as fertilizers. On the other hand, fertilizers increase the water-use efficiency. Such interactions must be closely studied so as to maximize the impact of inputs of agricultural production. The nutrients in the soil are always in a state of flux, with additions and subtractions. Monitoring the dynamics of the nutrients would promote their efficient use by crops and prolong the productive life of the soils. Several models currently exist for the study of organic matter dynamics in soils. These models should be applied to the West African situation since it is vital to develop management practices that can promote efficient use of nutrients released during mineralisation of soil organic matter. Judicious fertilizer use in West Africa should be promoted as this practice will enhance agricultural production while protecting the fragile environment.

Electronic Resource

1573-5036

acidity ; agroforestry ; aluminium ; Calliandra ; Grevillea ; Leucaena ; manure ; Oxisol

Springer Online Journal Archives 1860-2000

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Abstract Prunings of Calliandra calothyrsus, Grevillea robusta, Leucaena diversifolia and farm yard manure were applied each cropping season at 3 and 6 t dry matter ha−1 to an Oxisol in Burundi. The field plots also received basal applications of nitrogen (N), phosphorus (P) and potassium (K). Application of the tree prunings or farm yard manure decreased the concentration of monomeric inorganic aluminium (Al) in soil solution from 2.92 mg Al dm−3 in the control plots to 0.75 mg Al dm−3 in the plots receiving 6 t ha−1 Calliandra prunings. The other organic materials also decreased the concentration of monomeric inorganic aluminium in the soil solution. The lowered Al concentration led to a corresponding decrease in the percentage Al saturation of the 0–10 cm soil layer from 80% to 68%. Grain yields of maize and beans were strongly inversely related to the percentage Al saturation of the soil. This confirms that soil acidity was the main constraint to maize and beans production. The yield improvement was mainly attributed to the ameliorating effects of the organic matter application on Al toxicity. The nutrient content had less effect presumably because of fertilizer use. In the best treatments, the yield of maize increased from 0.9 to 2.2 t ha−1 and the corresponding beans yield increased from 0.2 to 1.2 t ha−1. A C Borstlap Section editor

Electronic Resource