Effect of seed invigouration treatments on nutrient uptake by crop
Uptake of N, P, K, Zn and B uptake by the crop at harvest was markedly influenced by seed invigouration treatments (Table 1 and 2). Compared to control, seed invigouration treatments registered higher uptake, due to higher dry matter production recorded in these treatments. Nutrient uptake by crop is related to nutrient content in the plant and dry matter production; dry matter production in turn depends on the photosynthetic ability of the plant. Enhanced seedling vigour resulting from the fast and uniform crop establishment might have led to the development of higher number of branches with more leaves with higher leaf area and chlorophyll content. This might have increased the photosynthetic rate and uptake of nutrients in seed invigouration treatments.
Tabassum et al., (2013) observed that increased availability of nutrients also accelerated the physiological processes which in turn influenced the nutrient uptake.
Among the seed invigouration treatments, total uptake as well as uptake of N, P and K by the grain was the highest in T
4 (seed priming with ZnSO
4 0.05 per cent for 4 h). This might be due to higher dry matter accumulation and higher content of N, P and K registered in the treatment. Higher uptake of N, P and K by grain in T
4 might be due to the role of Zn in activating the enzymes present in the chloroplast and cytoplasm
viz., carbonic anhydrase, fructose-1, 6-bisphosphate and aldolase enzymes and this will lead to the transport of photosynthates from source to sink.
Marschner and Cakmak (1989) pointed out that deficiency of Zn resulting in the accumulation of carbohydrate in plant leaves.
Pooniya and Shivay (2013) pointed out that Zn fertilization significantly improved the N and K uptake in Basmati rice grain and straw.
Khattak et al., (2006) reported that Zn nutrition improved the N uptake by maize crop. Similarly,
Karki et al., (2005) observed an increase in the uptake of nutrients due to Zn fertilization.
Zinc and B uptake were also significantly influenced by seed invigouration treatments (Table 2). Seed invigouration treatments recorded higher uptake of Zn and B compared to control. Better crop growth attained by the early establishment of seedlings might have resulted in better absorption and uptake of major nutrients along with micronutrients Zn and B. Among the seed invigouration treatments, treatments involving ZnSO
4 priming registered higher Zn uptake by the grain. In the present experiment, cowpea seeds primed in ZnSO
4 0.05 percent enhanced the Zn uptake of cowpea grain by 40.2 per cent. The result is in agreement with the observation of
Harris et al., (2007) who observed that Zn priming significantly increased the grain Zn concentration in maize and is a low-cost technology to augment the Zn content in grain.
Slaton et al., (2001) and
Miraj et al., (2013) also reported that nutripriming significantly enhanced the Zn uptake by rice seedlings. Borax pelleted seeds also recorded higher Zn uptake compared to control. The result is in conformity with the observation of
Debnath et al., (2018) who observed that application of B along with recommended dose of fertilizers increased the B uptake in grain cowpea. The B uptake by grain was the highest in ZnSO
4 primed seeds than in borax pelleted seeds.
Sinha et al., (2000) observed a positive Zn x B interaction in mustard.
Effect of seed invigouration on organic carbon content and available nutrient status
As compared to initial nutrient status, nutrient status of soil after the experiment was improved (Table 3). This was due to the fact that, being a leguminous crop, cowpea have the ability to fix atmospheric N and tap nutrients from deeper layers
(Melero et al., 2007). The result is in consonance with the observation of
Amanullah et al., (2007). Thamburaj (1991) revealed that raising legumes in rotation increased the NPK content of soil.
Jensen et al., (2012) also reported that inclusion of legumes in rotation significantly improved the soil organic carbon and available nutrients in the soil.
Post-harvest organic carbon content of soil was significantly influenced by seed invigouration treatments (Table 3). In general, an enhancement in organic carbon content of soil was observed in all the treatments compared to initial soil status. The enhancement in organic carbon content observed in all the treatments might be due to the uniform application of FYM 20 t ha
-1, biological N fixation, addition of organic residues and exudation of root exudates in to the soil by the crop root as well as the symbiotic N fixing bacteria associated with the crop. Seed invigouration treatments registered higher organic carbon content compared to control. This might be due to the enhanced crop growth resulting from the better seedling establishment and improved nodulation observed in these treatments.
Lynch and Whips (1990) revealed that about 40 per cent of dry matter accumulated by the plant was released into the rhizosphere as root exudates. Among the seed invigouration treatments, higher organic carbon content was observed in T
4 (seeds primed in ZnSO
4 0.05 percent for 4h) which was statistically comparable with T
1 and T
2 (seeds pelleted with borax 50 and 100 mg kg
-1 seed), T
3 (seeds primed in ZnSO
4 0.025 per cent for 4 h) and T
8 (T
1 +
Trichoderma viride seed treatment 10 g kg seed
-1) . This was also due to the increased nodulation and higher dry matter production observed in these treatments. Organic substances (organic acid, amino acid, sugars, vitamins, mucilage
etc.) released into the rhizosphere during the crop growth as well as due to the addition of organic matter in the form of FYM and leaf fall might have enhanced the organic carbon content of soil
(Hasanuzzaman et al., 2019).
Available N, P, K, Zn and B status of soil was also significantly influenced by seed invigouration treatments (Table 3). Compared to control, all seed invigouration treatments registered higher availability of N, P, K, Zn and B. The better crop establishment and better rooting allow the crop to tap nutrients from the deeper layers. Further organic matter addition due to the falling of senescent leaves and atmospheric N fixation by the symbiotic N fixing bacteria present in the nodule also contribute to the increased availability of N, P and K.
Chatterjee and Bandyopadhyay (2017) reported that seed treatment with micronutrients have prominent effect on the availability of major nutrients.
The available N status of all the treatments are in medium range. Availability of N was found to be higher in treatments with higher organic carbon content. The result is in accordance with the findings of
Sakin (2012) who reported that high soil organic carbon enhanced the N content of the soil. Available P status in the soil after the experiment was found to be high in all the treatments. However, the treatments having high Zn content registered lower available P content compared to those treatments having low Zn content. This might be due to the antagonism exists between Zn and P and also due to the formation of insoluble zinc phosphate. Similar observations were also made by
Balai et al., (2017). Available K status was comparatively higher in treatment T
7 and T
8 (seeds primed in ZnSO
4 0.025 and 0.05 per cent +
Trichoderma viride seed treatment 10 g kg
-1 seed) compared to other seed invigouration treatments which might be due to lower K uptake registered in these treatments.
Seed invigouration treatments registered higher available Zn and B content in soil compared to control (Table 3). This might be due to the fact that higher soil organic carbon content prevented the leaching of nutrients and sustained the soil fertility status. Similar observation was also made by
Suman (2018). Among the seed invigouration treatments, the treatments having higher post-harvest Zn content registered lower B content. This might be due to the antagonistic effect of Zn on B. The result is in agreement with the findings of
Mullah et al., (2015) and
Hosseini et al., (2007) who observed that higher Zn availability in soil decreased the B availability in soil.