Impact of N and P on growth, yield and nodulation of Bambara groundnut
The plant height, leaf area, nodule number, nodule weight, nitrogen yield, pod number and harvest index were investigated at harvesting time were significantly increased with different levels of applied N and P fertilizer (Table 1 and Fig 1). The mean highest plant height of 20.65 cm was recorded at T16 (N30P60 kg ha
-1) and gave 5.46% more advanced than T1 (control). The result also revealed that the growth of plants increased with the increasing N and P levels.
Hasan et al., (2019) also reported a similar effect where plant height decreased with decreasing N and P fertilizer. Highest increase in pod number and pod dry weight at N30P60 kg ha
-1 was reported by
Hasan et al., (2021). The number and weight of nodules were increased with N30P60 kg ha
-1 compared to other N and P fertilizer combinations. The highest nodule number of 38.00 was recorded at T16 (N30P60 kg ha
-1) followed by 34.75 at T15 (N30P40 kg ha
-1) and 33.75 at T8 (N10P60 kg ha
-1). These findings are similar to other studies (Egbe and Egbo, 2011). The most significant increase in the pod number was 74.28% at T16 (N30P60 kg ha
-1), followed by 65.71% at T12 (N20P60 kg ha
-1) and 53.33% at T4 (N0P40 kg ha
-1) compared to T1 control (control). There exists an increasing trend with increasing levels of N and P fertilizer. The finding of this experiment is similar to
Hossain et al., (2007), where N (0, 20, 40, 60 kg ha
-1 and P (0, 30, 60, 90 kg ha
-1) doses were applied and found the better growth and yield at N60P60 kg ha
-1.
Impact of N and P on mineral and proximate composition of seed
The results showed that calcium (Ca), magnesium (Mg) and manganese (Mn) content in bambara groundnut differed significantly due to the different levels of N and P application but have no significant difference was recorded on protein, fiber, ash, moisture, potassium (K), copper (Cu), iron (Fe) and sodium (Na) (Table 2). The highest value of Ca was illustrated at 660.00 mg kg
-1 at T13 (N30P0 kg ha
-1) and the lowest was 592.75 mg kg
-1 at T1 (control) (Table 2). Manganese content increased 70.45% at T16 (N30P60 kg ha
-1), followed by 61.36% at T12 (N20P40 kg ha
-1) and 56.06% at T4 (N0P40 kg ha
-1). The result mentioned that the mineral composition increased with increasing at a different level of N and P fertilizer but decreased where no fertilizer was applied. A similar finding was reported by
Hasan et al., (2019) that the mineral composition was increased at N30P60 kg ha
-1 compare to other fertilizer treatments. The amount of protein contains in seed at different levels of N and P was varied among 191.30 to 203.00 mg kg
-1. On the other hand, in this study bambara groundnut seeds contain 51.50 mg kg
-1 fibre, which was the same as the result obtained from Abdulsalami and Sheriff (2010) but higher than that of the result by
Mazahib et al., (2013). Nitrogen and P contribute significantly to the synthesis of fibre and protein and the higher N and P available to the crop, the higher protein can be synthesized.
Impact of N and P on amino acid content of seed
Application of N and P fertilizer at different levels had no significant impact on all amino acid content on the seed of bambara groundnut plant (Table 3). The seeds contain sufficient quantities of lysine, cysteine and methionine, such kind of essential amino acids. Amino acids content in seeds were decreased at T16 (N30P60 kg ha
-1) such as aspartic acid (2.32%), arginine (6.80%), cystine (13.64%), glumatic acid (2.03%) and histidine (6.23%) in comparison to T1 (control). It is seen that aspartic acid, glumatic acid and leucine are the most abundant amino acids in all the samples.
Olaleye et al., (2013) reported the same result. However, the amino acids contained in the seed were lower than the result reported by
Mazahib et al., (2013).
Bambara groundnut is an edible legume that serves as one of the primary sources of income for smallholder farmers. Our findings indicated that N and P fertilizer significantly influenced the growth, yield, nitrogen content and nutritional composition of bambara groundnut. This is a clear indication that N30P60 kg ha
-1 increases the growth, yield, nitrogen content and nutritional composition of bambara groundnut rather than other fertilizers.