Agriculture Reference
In-Depth Information
Flowering Response
There is no evidence that B deficiency prevents initiation of or delays floral develop-
ment.When plants are grownwithout B or are transferred into B-free nutrient solutions
in pot experiments, the apical meristems may abort and therefore flowers do not
develop, as shown for peach (
Prunus persica
;KamaliandChilders
1970
). However,
under field conditions, where B deficiency stresses occur more gradually, plants may
have time to adapt to deficiency. For example, in peanut (
Arachis hypogaea
), the
flowering period was extended in B-deficient plants (Harris and Brolman
1966
),
resulting in low-B plants producing as many flowers as B-adequate plants. In species
where the flowers occur in compact inflorescences, and these are terminal on the stem
(e.g. sunflower, wheat), low B has a greater impact on reproduction because the plant
has less ability to modulate reproductive growth than species with axillary inflores-
cences and indeterminate growth. The first group of plants is more prone to pollen
sterility under low B than the latter group of plants. Experiments on wheat by Li
et al. (
1978
), suggested that absorbed B was transported from soil to floret and spikelet
organs, which resulted in accumulation of B in seeds. Finally, lowB can result in plants
being functionally male sterile (e.g. wheat, Li et al.
1978
; rice, Garg et al.
1979
;
barley, Simojoki
1972
), although cases of female sterility have been reported
(e.g. maize, Vaughan
1977
; avocado, Coetzer and Robbertse
1987
). The external B
supply does not appear to alter the frequency of unisexual flowers, although some
workers have attempted unsuccessfully to do this by applying B sprays (Singh
1994
).
Effect of B on Nutrient Use Efficiency, Demand and Supply
Nutrient use efficiency (NUE) may be expressed as productivity of the plant per
content of applied nutrients. Enhancement of NUE is vital for improvement of crop
production in marginal lands with poor nutrient availability. NUE for plants is
reliant on the ability to efficiently take up nutrients from the soil, but also on
translocation, storage and usage within the plant, and on the environment (North
et al.
2009
). NUE is largely dependent on nutrient availability in the soil or applied
medium. Nutrient demand and supply (NDS) is how efficiently the plant can fulfil
the demand and supply rate for required nutrients at different stages and conditions
of plant growth and development. Under limiting conditions of nutrients, plants
showed decreases in nutrient uptake compared to sufficient nutrient conditions
(preserving the nutrition for future demand).
Large variations in defining nutrient efficient plants and methods used in calcu-
lating nutrient use efficiency, makes it difficult to compare results of different
studies. The effort to measure yield response to an applied nutrient is further
confounded by other factors, such as variable soil fertility levels, climatic condi-
tions, crop rotations, and changes in production practices that affect nutrient use
efficiency (Stewart et al.
2005
). In simple terms, efficiency is the ratio of output
