Partitioning differences between genotypes are also attributed to ability of genotypes to initiate pods under drought conditions. The ability to produce pods under drought and the ability to recover from drought with greater pod growth are two different mechanisms for higher yields under drought conditions. Studies have also indicated that pods that are initiated and developed under drought stress conditions have lower seed quality in terms of reduced germination and seedling vigor.
10.3. Nutrient Stress Nitrogen (N) - Groundnut being a legume, meets its nitrogen (N) requirements through a symbiotic relation with bacteria (Bradyrhizobium spp.). Generally, most soils will have nitrogen fixing bacteria in them; however, it may be beneficial to inoculate seeds with rhizobia to ensure nitrogen fixing. Inorganic N fertilization is not typically recommended in United States, except in regions where nitrogen fixation is low.
In India and Africa, a starter dose of 10-15 N/ha kg is recommended until the symbiotic nitrogen fixation is fully functional. Studies have also shown that higher doses of nitrogen application inhibit biological fixation. If nitrogen deficiency symptoms (yellowing of older leaves) are observed, a top dressing with nitrogen can be recommended. Phosphorus (P) is an important nutrient for groundnut. Most of the groundnut production regions in Africa and Asia are deficient in P. On a global scale P is probably the most deficient nutrient element for groundnut production.
Its deficiency usually occurs in soils with
low organic matter, or in soils which are brought into cultivation recently and
never have been fertilized with P before. In addition, soils with a long
cropping history without any application of P fertilizer also show this
deficiency. Soils which are rich in Fe also induce P deficiency due to fixation
of P by the iron compounds.
This deficiency can easily be corrected by applying P fertilizer at the time of planting. Common sources of P fertilizer include rock phosphate, single super phosphate, triple super phosphate and diammonium phosphate. Foliar application of P is also used in areas where P fixation is problem. Potassium (K) deficiency is not common in groundnut, due to its low requirement compared to soybean and other legumes. However, in soils with low organic matter content groundnut can respond to K application. In semiarid regions of Asia and Africa the crop can respond to application of K.
In India, K supply at the time of planting is
often recommended in order to improve oil and protein concentration in the
kernels. Calcium (Ca) is by far the most important nutrient for pod
development. The crop has a very high Ca requirement; about 90% Ca is absorbed during flowering
and pod formation and development. The required Ca for pod and seed development
must be absorbed by the gynophore (peg) and developing pods via passive uptake
through diffusion. Calcium absorbed from roots and stored in leaves cannot be
moved into pods.
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