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Boron is an essential micronutrient element required for plant growth. Boron deficiency is wide-spread in crop plants throughout the world especially in coarse-textured soils in humid areas. Boron toxicity can also occur, especially in arid regions under irrigation. Plants respond directly to the B concentration in soil solution and only indirectly to the amount of B attached to soil surfaces (Keren et al. 1985). Therefore, the soil adsorption complex acts as both a source and a sink for dissolved B and can mitigate phytotoxic soil solution B concentrations.

Plants vary in their B requirement but the range between deficient and toxic soil solution concentration of B is very narrow than for any other nutrient element. In arid and semi arid regions, B toxicity results from high levels of B in soils and from addition of boron via irrigation water. However, B deficiency is of great concern in areas receiving heavy rainfall. Compared with other micronutrients, chemistry of B in soils is very simple. Boron doesn’t undergo oxidation-reduction reactions or volatilization reaction in soils. Boron containing minerals are either insoluble (Tourmaline) or very soluble (Hydrated B minerals) and generally do not control the solubility of B in soil solution (Goldberg et al. 1993). Boron concentration in the soil solution is generally controlled by B adsorption reaction as is the amount of water soluble B available for plant uptake.

Boron is an essential micronutrient element required for the normal growth of plants. The range between boron deficiency and toxicity symptoms in plants is typically narrow, in the range of 0.028 to 0.093 mmol/L for sensitive crops and 0.37 to 1.39 mmol/L for tolerant crops (Goldberg, 1997). Much work has been done on plant availability of boron and physico-chemistry of boron in soil, but generally not in combination. Availability of boron to plants is affected by a variety of soil factors including soil solution pH, soil texture, soil moisture, temperature, oxide content, carbonate content, organic matter content, and clay mineralogy (Goldberg et al. 2000). However, these soil properties are functions of the physico-chemistry of soils, so that determination of relationships between plant availability of boron and the physico-chemical properties of boron in soils has still tremendous interest for us. This article summarizes results about plant availability of B, physico-chemical properties of soil B, chemical behavior of common B soil minerals and their relationships.

Mango (Mangifera indica. L) is grown in 1.1 m ha in India in different climatic zones ranging from humid tropics receiving 2500 mm annual rainfall to semi arid tropics (600-900mm rainfall) and subtropics (800–1000mm rainfall). It is also grown in soils widely varying in its physico chemical properties. The pH of mango orchards range from a low of 4.5-5.2 in Konkan, Maharashtra to 7.2 to 8.1 in Uttar Pradesh and Chittor, Andhra Pradesh and accordingly it is affected by different types of macro and micronutrient disorders based on soil properties Boron deficiency is one of the important micronutrient disorders affecting mango both in high rainfall areas (Edward Raja et al 2005) and in semi arid tropics and average productivity is low at 6-7 t ha.

The plateau in Pakistan (Fig. 1; latitude 32° 10' to 34° 9' N; longitude 71° 10' to 73° 55' E) is part of the great Indo-Gangetic synclinorium, separated from it, and elevated, at the end of the Tertiary Period. The plateau spans over 1.82 million hectare (Mha) and constitutes a major rainfed tract in the north of Punjab province, Pakistan (Fig. 2). It is situated in the north of Salt Range, in-between rivers Jehlum and Indus. Its climate is semi-arid to sub-humid continental. Rainfall pattern in the plateau is bi-model; the maximum being in late summer and winter-spring (Fig. 3).

Boron is distributed in nature very widely. The average content of boron in the earth’s crust is 1×10. More than 150 boron minerals have been found, but only about ten of them are currently in use. The chemical composition of boron minerals is divided into three types: borosilicate minerals, boro-alumino-silicate minerals and borate minerals (including those containing water and anhydrous borate minerals).

There were some reports containing information on micronutrients in citrus area (Kausar et al. 1979; Rashid et al. 1991). Upon looking the details, it was found that existing information were limited and unsystematic. The samples were collected disregarding the time and age of plant tissues during sampling which is very important aspect. To establish nutrients deficiency in fruit plants, the age of leaves taken from bearing and non-bearing branches are extremely important. These aspects were mostly lacking from the existing information. Keeping in view the previous work done in Pakistan, more appropriate efforts have been made in this study to investigate soil and plant micronutrients status of citrus growing area on high-pH calcareous soils.