Application of phosphogypsum @ 125 kg S eq ha1 in split together with recommended dose of NPK recorded highest number of pods plant
-1 (38.33), kernels plant
-1 (75), kernel yield plant
-1 (26.08 g), test weight (34.79 g), pod yield (2063 kg ha
-1), kernel yield (1418 kg ha
-1) and haulm yield (4004 kg ha
-1) (Table 1) which recorded on par results with phosphogypsum @ 100 kg S eq ha
-1 applied in split. At the same time, application of same amount (125 and 100 kg S eq ha
-1) of phosphogypsum as basal alone recorded significantly lower values than split application in all the parameters except test weight, where difference is not significant (Table 1). These results support the earlier studies made by
Kannan et al., 2017; Kumar et al., 2011; Manaf et al., 2017. As the calcium is key nutrient element which is part of cellular membrane and promotes the tissue growth, has also recorded its importance in pod formation and pod filling
(Sahu et al., 1999). Though the present experiment was designed on the basis of sulphur equivalence, phosphogypsum also supplies calcium in substantial amounts. Whereas, sulphur is known for its protein synthesis function
(Rashmi et al., 2018; Rao et al., 2013) which in turn promotes vegetative growth through active photosynthesis thus, the effects of calcium and sulphur synergistically acted upon physiology of the plant to yield present results.
Sufficient number of pods observed in many treatments (T
9, T
8, T
5, T
4 and T
1) but number of filled pods or number of kernels plant
-1 varied greatly with different amounts of phosphogypsum. In treatments with split application of 125 and 100 kg S eq ha
-1, maximum number of kernels were noticed due to sufficient quantities of available S and Ca (which helps in pod filling) in addition to NPK when compared with other treatments. When phosphogypsum was applied in two equal splits (basal and 30 DAS) response was greater than applying entire dose as basal, similar findings were made by
Sahu and Das (1997). In each treatment incremental results were noticed with phosphogypsum, compared with treatments without phosphogypsum.
Similar to number of kernels, kernel yield plant
-1 also followed same trend where split application of phosphogypsum at 125 kg S eq ha
-1 recorded highest pod yield plant
-1 followed by 100 kg S eq ha
-1 in split (Table 1). This is because greater number of filled pods in above treatments compared with others. Whereas lower yield is due to unavailability of nutrients (Ca and S) responsible for pod filling in sufficient quantities at times of need. This proved that both quantity and time of nutrition are important factors in deciding yield.
At the initial growth stage (30 DAS), treatment receiving phosphogypsum @ 100 and 125 kg S eq ha
-1 as basal and gypsum @ 500 kg ha
-1 recoded on par sulphur uptake but the highest uptake (6.84 kg ha
-1) was noticed with phosphogypsum @ 125 kg S eq ha
-1 (Table 2) which is due to the presence of greater amounts of available sulphur in soil when compared to other treatments. Whereas, at remaining times of study
i.e., 60, 90 DAS and at harvest, treatment with split application of phosphogypsum @ 125 kg S eq ha
-1 recorded highest sulphur uptake. In all the treatments, sulphur uptake was maximum at initial 30 days and later on it progressively reduced as the growth continues (Fig 1). The reduction was greater in treatments with basal application of phosphogypsum. On the other hand, treatments with split application had advantage over basal application at later growth stages. As the efficient utilisation of nutrients in groundnut commences from peg initiation to pod filling
(Kumar and Shivakumar, 1990), split application of sulphur source (phosphogypsum here) ensured sufficient quantities of sulphur at times of crop requirement, which has been evidenced in the experiment. Gypsum also followed similar pattern like phosphogypsum in terms of sulphur uptake but gypsum was applied as basal alone so, its uptake values are comparatively lower than split applied phosphogypsum. While supplying sulphur through SSP alone without any additional source, recorded very low values of uptake which suggests its inadequacy.