Publisher Summary This chapter discusses the place occupied by molybdenum (Mo) in the agronomy that services the agriculture on which the world depends for food. The detailed results from a number of disciplines are shown to be integrated into a mature body of knowledge concerning Mo in agricultural practice. In addition, it indicates some of the likely biological effects in the biosphere, and hence, broader applications of scientific effort. Sodium and ammonium molybdates are common Mo fertilizers. The practice of adding solid Mo compounds to another fertilizer as carrier for application to the soil can lead to uneven distribution. The main physiological role of Mo in plants appears to be its participation in two important enzyme systems—namely, nitrogenase, and nitrate reductase, but others may also be involved. Changes in nitrate reductase activity and overall content of Mo are associated with yield responses. Geographically, most of the responses have been reported from lightly acid soils in temperate countries. Many crop plants are consumed by animals, and the Mo status of the plant can affect the animal that eats it. Deficiencies of Mo in livestock have not been reported, but toxicity does occur and is associated with disturbance of copper metabolism.

Molybdenum in Soils, Plants, and Animals

The purpose of soil testing is to determine which nutrients are deficient in a given field and, if possible, to estimate how much fertilizer is needed. Soil testing for micronutrients is particularly difficult because plant requirements for these elements are relatively low and even slight contamination of a sample or modification of a procedure may seriously affect soil test results.

Micronutrient soil testing for the tropics

Availability Assays for the Secondary and Micronutrient Anions

Molybdenum (Mo) is an essential element of plants and animals and is of concern from human nutrition and environmental standpoints. Rational applications to soil of Mo in fertilizers, sewage sludges, or other soil amendments requires information of the concentrations of Mo in soils and plants. Two greenhouse experiments were conducted at Lexington, Kentucky, using surface samples of 12 soils (11 soil types) derived from diverse parent materials in Kentucky with soil pH ranging from 5.18 to 7.46. Molybdenum (Na2MoO4.2H2O) was added at rates equivalent to 0, 0.3, and 0.6 mg Mo kg‐1 soil. Tobacco (Nicotiana tabacum L., cv. Ky14) and soybean [Glycine max. (L.) Merrill cv. McCall] were grown to provide plant Mo data for Mo soil test correlations and comparisons. The primary purpose of these investigations was to determine the effect of pH of NH4‐oxalate extractant solution on the relationship of soil Mo and Mo uptake by tobacco and soybeans, and to evaluate the automated KI‐H2O2 procedure for use in d...

Effect of pH of ammonium oxalate extracting solutions on prediction of plant available molybdenum in soil

A study was conducted to establish the uptake of micronutrients by two Acacia Senegal varieties established under arid and semi-arid conditions, and its subsequent effect on the quality of gum arabic exudates. Soil and gum arabic samples from the experimental sites at Solit, Kapkun, Kimorok and Maoi in Marigat division, Baringo district, were collected, dried and analysed to establish their baseline physical and chemical characteristics. Glasshouse pot experiments were conducted using the same soil and vermiculite media to determine uptake of copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn) by Acacia Senegal seedlings. A randomized, split-plot design that simulated the environmental conditions in the field was used in treatments varying from normal, low and high concentrations of the micronutrients applied. The soil types varied significantly (P < 0.05) in the level of calcium (17.3, 5.7, 6.4 and 5.0 cmol. (+)/kg) and magnesium (6.1, 3.3, 4.0 and 2.7 cmol. (+)/kg), respectively, at the study sites. The average copper uptake (103 ppm) by Acacia Senegal variety Senegal in Solit on dry matter (DM) basis was significantly higher (P < 0.05) than that at Maoi (41 ppm), Kimorok (33 ppm) and Kapkun (30 ppm). Gum arabic from Acacia Senegal variety Senegal in Kapkun and Solit had concentrations of 45 and 40 ppm Cu, which reveal that Acacia Senegal variety Senegal tends to take higher Cu levels (108 and 156 ppm) from the soils than that of Acacia Senegal variety kerensis at Kimorok and Maoi (38 and 32 ppm). Iron and manganese uptake by the variety (654 and 638 ppm) at Kapkun was significantly higher (P < 0.05) than that of the variety at Kimorok (366 ppm Fe and 307 Mn), respectively.

H. F. Massey

Papers

Hot Water Extraction for Available Soil Molybdenum