Effect of Lime on Boron Transport to and Uptake by Cotton

Deficiencies of Boron have occurred in cotton (Gossypium hirsutum L.) grown in coarse textured soils during periods of moisture stress and in those soils which have been recently limed. These B deficiencies have generally been attributed to a decrease in soil B availability to cotton. As a result a greenhouse experiment was conducted to study (i) the amounts of adsorption and diffusivity rates of B in two silt loams and (ii) B absorption by cotton grown in pots. Addition of lime increased B adsorption by both a Taloka silt loam and a Calloway silt loam. Maximum B adsorption occurred on the seventh day after its addition but did not differ appreciably from the one day equilibration time. The adsorption data could not be accurately described by the Langmuir adsorption equation. Increasing amounts of lime and decreasing soil water content caused a decrease in B diffusivity in the two soils. Diffusivity values when averaged over all treatments were 4.6 × 10⁻⁶ and 2.7 × 10⁻⁶ cm²/sec for the Calloway and Taloka soils, respectively. The addition of lime to the Taloka soil reduced the growth and rate of development of cotton grown in greenhouse pots. Plant parameters such as date of emergence, plant height, dry weight accumulation, total B content, root length and root surface were reduced by the lime addition. The rate of B absorption by cotton decreased until square initiation then increased. This result suggests that cotton has differing B requirements during the growing season and that these requirements are highest during the early growth stages and fruit formation. Even though the total amount was lower, the rate of absorption of B by those plants growing in the limed soil was greater than those growing in the soil which received no addition of lime. This was attributed to the lime having a greater effect in reducing the magnitude of root surface area as compared to its effect in reducing the rate of B transport within the soil.