Abstract: Background and Objective: Adequate yield improvement in groundnut may not be achieved in acid sand Ultisol through the application of mineral phosphorus alone, however, a combined application of lime and phosphorus fertilizer may be a better management option in such soils. Hence, this study evaluated the effects of four levels of lime (0, 2.0, 4.0 and 8.0 t ha–1) and four phosphorus (P) levels (0, 25, 50 and 75 kg ha–1) on the performance of groundnut (Arachis hypogaea L.) in the humid rainforest of South Eastern Nigeria. Materials and Methods: The study was a factorial experiment laid out in a Randomized Complete Block Design (RCBD) and consisted of sixteen treatment combinations replicated three times each. Results: The result obtained showed that the application of phosphorus fertilizer and lime had a significant (p<0.05) effect on plant height, number of leaves per plant, number of branches per plant, 75 kg ha–1 P and 8.0 t ha–1 lime resulted in the highest growth parameter. Similarly, 75 kg ha–1 P and 8.0 t ha–1 lime significantly improved the number of pods per plant 30.67, pod yield 3.58 t ha–1, biomass yield of 4.68 t ha–1, seed yield of 2.1 t ha–1 and 100 seed weight of 44.58 g, seed yield of groundnut while curtailing the number of unfilled pods 2.33. Conclusion: Application of phosphorus and lime at 75 kg ha–1 P and 8.0 t ha–1 lime is a beneficial agronomic practice that could enhance the productivity of groundnut in the Calabar rainforest zone of Cross River State.
INTRODUCTION
Groundnut production is constrained by Phosphorus (P) and Calcium (Ca) deficiency in many soil types1,2 and in the humid tropical rainforest zone in Calabar, it is aggravated by the acidic nature of the acid sand geological material of the Ultisol which is the dominant soil type in the region. The nutrient status and mineralogy of acid sand bear the imprints of quartz arenite which is not rich in most plant growth nutrients3 and usually gives low crop yield if there is no application of external inputs.
According to Vance et al.4, 30-40% of soils globally including the most fertile soils are deficient in available P. Also, more than 80% of applied P becomes unavailable for plant growth because they are chemically bound as phosphates of Fe and Al owing to a high level of soil acidity or much of it may be converted to organic forms5,6. The tendency for P to form relatively insoluble compounds in Ultisol makes it a major source of concern in soil fertility management. Phosphorus, a major nutrient that constitutes about 0.2% of plant dry matter is known to play essential roles in photosynthesis, nodulation/nitrogen fixation, respiration, energy generation among others4. Therefore, to optimized crop yield in P deficient soils, application of P fertilizer is usually recommended.
Nearly 30% of the world’s land area comprises acidic soils and these soils are mostly found in tropical and subtropical regions7 and are P deficient due to excess Al3+, Fe2+ and H+ ions over Ca, Mg, K, etc.8. Nevertheless, liming is the most effective soil management practice to reduce the deleterious effects of soil acidity9. Improvement in the growth and yield of groundnut in particular and indeed other leguminous crops in acid sands vis-a-vis their P requirements can most likely be achieved through the combined application of P fertilizer and lime10-12.
The pH range of 6.0-6.5 is suitable for most crops, ranges lower than 5.5 usually require liming to neutralize excess H+ and/or Al3+ before the soil can support good yields13. Several studies in acid sand Ultisol in Calabar have indicated the pH of the area to be less than 5.56,14,15. Hence, there is a need for liming. Liming the soil with suitable conventional liming materials such as calcium carbonate (CaCO3), Magnesite (MgCO3), Hydrated lime {Ca(OH2)}, quicklime (CaO), dolomite [CaMg (CO3)2], etc., apart from providing Ca and/or Mg for groundnut nutrition, also helps to reduce soil acidity by displacing H+ and Al3+ from the adsorption site thus counteracting high soil acidity16, limit the toxicity effects of some micro-nutrients by lowering their concentrations in the soil solution and increasing the availability of other essential plant nutrients such as P, N, K and Mg in the soil16,17 and also enhancing soil conditions for beneficial microbial organisms responsible for mineralization18.
Various researches have been done on the effects of P and lime on a wide variety of soils and crops globally, for example, combining lime and P fertilization gave a high available soil P while several other kinds of research have indicated positive effects of liming on crop growth and yield19-24.
The adoption of combined use of lime and P fertilizer as a soil fertility management option is not yet significantly practised by farmers in South-eastern Nigeria, although some studies have already been published. The positive effect of lime on crop uptake and soil nutrient status has also been documented by Opala25 and Kisinyo16. There is however a possibility that the rate of applications recommended elsewhere may not be effective on acid sand Ultisol in Calabar, because of high rainfall coupled with excessive leaching, the type of soil parent material among other factors. There still exists a paucity of information on the combined application of lime and P on groundnut production in Nigeria. Therefore, this research seeks to evaluate the effect of lime and P on groundnut on the Ultisol of the humid forest zone of South Eastern Nigeria.
MATERIALS AND METHODS
Study area: Field experiments were carried out in the 2018 and 2019 planting seasons at the University of Calabar Teaching and Research Farm, Nigeria. Calabar is located in the humid forest zone of Nigeria (Latitude 04°57’ N and Longitude 08°19' E) and has a bimodal annual rainfall distribution that ranges from 1500-2500 mm per annum, mean annual temperature and relative humidity of 27°C and 83%, respectively, on an altitude of about 39 m above sea level.
Methodology: The experiment was a 4×4 factorial arranged in a randomized complete block design. The treatments consisted of factorial combinations of 4 levels of lime (0, 2.0,4.0 and 8.0 t ha–1) and 4 levels of phosphorus (0, 25, 50 and 75 kg ha–1) resulting in 16 treatment combinations each of which was replicated thrice. Each experimental unit measured 3.0×2.5 m. Two seeds of groundnut were planted per hole and thinned to one plant per stand. Hydrated lime {Ca(OH)2} was used as the source of lime whereas single super-phosphate was the source of phosphorus used for the experiment and was applied at planting. Groundnut seeds were planted at a distance of 50 cm between rows and 30 cm within rows (66,600 plants ha–1). The plots were weeded by hand-pulling within the crop rows and hand-hoeing between rows at 2 and 4 Weeks After Planting (WAP). During weeding, the bases of the groundnut plants were earthed up to protect developing pods as well as provide a loose medium to ease their penetration and enlargement.
Data Collection: Data were collected from 5 tagged plants in the middle rows of groundnut stands from each plot on the following growth, yield and yield attributes, plant height, number of branches, number of leaves, leaf area, number of nodules, the total number of pods, number of unfilled pods, above-ground biomass, pod yield, seed yield, 100 seed weight, threshing percentage, harvest index, dry matter yield.
Before planting, soil samples were collected at a depth of 0-20 cm with the aid of a soil auger and were thoroughly mixed in a Ziploc bag to obtain a homogenized sample. These samples were adequately labelled and transported to the laboratory for analysis. The samples were air-dried, ground and passed through a 2 mm sieve and subjected to Physico-chemical analysis using methods as outlined in Estefan et al.26. To determine the dry matter, sample plants were cut at the ground level and oven-dried at 60°C for 48 hrs until a constant weight was obtained.
Statistical Analysis: Data collected were subjected to statistical analyses following analysis of variance (ANOVA) procedures for factorial experiment dispersed in a Randomized Complete Block Design (RCBD). Significant mean values were compared using Fisher’s Least Significant Difference (FLSD) at a 0.05 level of probability.
RESULTS
Pre-cropping soil analysis: The results for pre-cropping soil analysis showed that the sand, silt and clay contents were 81.94, 10.06 and 8%, respectively for the 2018 cropping season while in the 2019 cropping season the observed texture for sand, silt and clay were 78.96, 13.0 and 8.04%, respectively. The texture of the studied soil was sandy loam for both the 2018 and 2019 cropping years. The observed soil pH was 5.40 and 5.59 for the 2018 and 2019 cropping years, respectively. The organic carbon contents of the soil were 1.68 and 1.75 % for the 2018 and 2019 cropping years. Total nitrogen of the 2018 cropping year was 0.14% while that of the 2019 cropping year was 0.12%. The available phosphorus content of the soil was 26.59 and 32.14 mg kg–1 for the 2018 and 2019 cropping years. The exchangeable cations (Ca, Mg, K and Na) were all low in both cropping years. The exchangeable acidity of the soil were 1.55 and 1.60 cmol kg–1. The Effective Cation Exchange Capacity (ECEC) of the soil were 3.05 and 4.50 cmol kg–1 for the 2018 and 2019 cropping years, whereas, base saturation of the soil were 66.0 and 73.77% for the 2018 and 2019 cropping years in Table 1.
Effects of lime and phosphorus application on the vegetative growth of Arachis hypogaea: Effect of lime on the vegetative growth of groundnut are summarized in Table 2. Lime application at 3 t ha–1 significantly increased plant heights above other rates of application in 2018 whereas, in 2019, every successive increment in lime rate had a corresponding significant increment in plant height. Generally, the zero application rate had the least growth increment except in 2018 where it was at par with 2 kg ha–1 lime (Table 2). Branching was significantly influenced by lime application in 2019 and not in 2018 (Table 2). Plants treated with lime irrespective of the rate had a statistically similar effect on the number of branches produced but were significantly higher compared to no application. The number of leaves and leaf area expansion per plant was significantly influenced by lime application rate in both years of study. Every successive increment in lime application rate led to a corresponding significant increment in the number of leaves and leaf area expansion per plant in the order 8>4>2 t ha–1 and all lime treated plot produced significantly more and larger leaves compared to untreated plots
Phosphorus (P) had a significant effect on the plant height of A. hypogaea (Table 2). In the 2018 cropping year, applications of 50 and 75 kg P ha–1 had statistically similar plant heights which were significantly higher than the 25 kg P ha–1 application. Zero P application produced plants with the least plant heights. However, in 2019, the increment in the plant heights was in the order 75>50>25>0 kg P ha–1 and each preceding higher rate had a corresponding significantly higher effect than the other. P application did not have any significant effect on the number of branches produced (Table 2). Both the number of leaves produced per groundnut plant leaf area expansion were significantly influenced by P application in both years of study (Table 2). There were no significant differences between the number of leaves and leaf area at 50 and 75 kg P ha–1 but leaf production and leaf area expansion was significantly lower at Zero P application compared to all the plots that were treated with lime.
Significant interaction effects of lime and phosphorus were observed in the number of leaves only in 2018 and in plant height in 2019 (Table 2).
| Table 1: Pre-cropping physicochemical properties of the soil used for the study | ||
| Values | ||
| Soil properties | 2018 |
2019 |
| Physical properties | ||
| Sand (%) | 81.94 |
78.96 |
| Silt (%) | 10.06 |
13 |
| Clay (%) | 8 |
8.04 |
| Texture | Loamy sand |
Loamy sand |
| Chemical properties | ||
| pH | 5.4 |
5.59 |
| Total nitrogen (%) | 0.14 |
0.12 |
| Available phosphorus (mg kg–1) | 26.59 |
32.14 |
| Organic carbon (%) | 1.68 |
1.75 |
| Exchangeable potassium (cmol kg–1) | 0.15 |
0.19 |
| Exchangeable calcium (cmol kg–1) | 2.19 |
3.33 |
| Exchangeable magnesium (cmol kg–1) | 0.64 |
0.9 |
| Exchangeable sodium (cmol kg–1) | 0.07 |
0.08 |
| Exchange acidity (cmol kg–1) | 1.55 |
1.6 |
| Exchangeable cation exchange capacity (ECEC) (cmol kg–1) | 3.05 |
4.5 |
| Base saturation (BS) (%) | 66 |
73.77 |
| Table 2: Effects of phosphorus and lime on plant height, number of branches, number of leaves and leaf area of Arachis hypogaea | ||||||||
| 2018 | 2019 | |||||||
| Treatments | PH |
NOB |
NOL |
LA |
PH |
NOB |
NOL |
LA |
| Lime (L) | ||||||||
| L0 | 15.24 |
2.93 |
19.21 |
893.74 |
15.09 |
3.38 |
10.13 |
908.73 |
| L1 | 16.84 |
3.24 |
21.26 |
917.83 |
17.06 |
4.15 |
11.13 |
935.17 |
| L2 | 19.58 |
3.39 |
23.19 |
939.28 |
19.59 |
4.47 |
11.87 |
950.06 |
| L3 | 22.29 |
3.57 |
24.23 |
961.95 |
23 |
4.56 |
13.01 |
974.93 |
| LSD (0.05) | 1.65 |
NS |
0.77 |
10.78 |
0.7 |
0.5 |
0.36 |
20.85 |
| Phosphorus (P) | ||||||||
| P0 | 20.23 |
4.01 |
16.09 |
875.95 |
20.21 |
3.67 |
10.66 |
908.2 |
| P1 | 25.03 |
4.28 |
22.14 |
917.89 |
25.31 |
4.03 |
17.24 |
937.76 |
| P2 | 28.33 |
4.79 |
24.51 |
954.54 |
29.03 |
4.36 |
18.54 |
957.35 |
| P3 | 28.69 |
4.83 |
25.15 |
964.43 |
29.21 |
4.51 |
18.23 |
965.56 |
| LSD (0.05) | 1.65 |
NS |
0.77 |
10.78 |
0.7 |
NS |
0.36 |
20.85 |
| Interaction (L×P) | ||||||||
| L0P0 | 17.17 |
3.8 |
12.47 |
830.14 |
17.21 |
3 |
8.13 |
863.95 |
| L0P1 | 19.83 |
3.83 |
18.13 |
891.84 |
19.04 |
3.23 |
14 |
899.38 |
| L0P2 | 24.97 |
3.99 |
22.6 |
919.63 |
24.48 |
3.6 |
18.27 |
923.96 |
| L0P3 | 23.97 |
4.07 |
23.63 |
933.37 |
24.13 |
3.67 |
18.37 |
947.62 |
| L1P0 | 17.8 |
3.9 |
15.53 |
856.16 |
18.28 |
3.73 |
10 |
902.41 |
| L1P1 | 23.4 |
4.1 |
22.13 |
903.44 |
23.42 |
3.97 |
17.1 |
928.09 |
| L1P2 | 26.5 |
4.83 |
23.7 |
952.83 |
26.33 |
4.33 |
18.87 |
952.15 |
| L1P3 | 26.17 |
4.95 |
23.67 |
958.89 |
26.54 |
4.57 |
17.4 |
958.02 |
| L2P0 | 20.8 |
4 |
17.13 |
894.83 |
20.2 |
3.93 |
11.47 |
922.65 |
| L2P1 | 25.73 |
4.5 |
24 |
929.07 |
26.23 |
4.3 |
18.53 |
950.54 |
| L2P2 | 29.17 |
5 |
25.63 |
958.32 |
29.46 |
4.67 |
18.4 |
960.4 |
| L2P3 | 31.8 |
5.05 |
26.01 |
974.89 |
31.91 |
4.97 |
17.47 |
966.64 |
| L3P0 | 25.17 |
4.33 |
19.23 |
922.67 |
25.17 |
3.99 |
13.03 |
943.78 |
| L3P1 | 31.17 |
4.67 |
24.29 |
947.18 |
32.57 |
4.62 |
19.33 |
973.05 |
| L3P2 | 32.67 |
5.33 |
26.09 |
987.37 |
35.87 |
4.82 |
18.63 |
992.9 |
| L3P3 | 32.82 |
5.27 |
27.3 |
990.56 |
34.28 |
4.83 |
19.67 |
989.97 |
| LSD (0.05) | NS |
NS |
1.53 |
NS |
1.39 |
NS |
0.71 |
NS |
| PH: Plant height, NOB: Number of branches, NOL: Number of leaves, LA: Leaf area, L0: 0, L1: 2, L2: 4 and L3: 8.0 t ha–1 of lime, P0: 0, P1: 25, P2:50 and P3: 75 kg ha–1 of phosphorus fertilizer, LSD: Least significant different | ||||||||
In 2018, integration of 8 t ha–1 lime and 75 kg ha–1 P produced the highest number of leaves but this was not significantly higher compared to 8 t ha–1 lime and 50 kg ha–1 P or when 4 t ha–1 lime and 75 kg ha–1 P were applied. However, the least number of leaves were produced when neither lime nor P was applied (control plot).
Effects of lime and phosphorus application on the yield and
yield parameters of Arachis hypogaea: The application of lime had a significant effect on yield contributing attributes of groundnut except for harvest index. While in 2018, each successive increment in lime rate led to a corresponding increment in the number of nodules produced significantly. In 2019, a lime rate of 8 t ha–1 produced a significantly higher number of nodules compared to other rates of the application except 4 t ha–1 (Table 3). Data for the total number of pods per plant as shown in Table 3 revealed that every successive increase in lime rate led to a corresponding significant increase in the number of pods produced whereas, in both years, the number of unfilled or unproductive pod decreased significantly with each successive increment in the lime rate with the highest lime rate having the least number of unfilled pods.
Application of 8 t ha–1 lime produced the highest Above the Ground Biomass (AGB) but this did not significantly different from AGB at 4 t ha–1 lime but the plot with zero lime application had the least AGB (Table 3). The total pod yield as shown in Table 4, indicates that 4 and 8 t ha–1 lime did not differ significantly but were significantly higher compared to 2 t ha–1 lime whereas the plot which received no lime application had the least pod yield in 2018. In 2019, the pod yield increased significantly with each successive increment in lime rate (Table 4). Seed yields were statistically the same for plots treated with 4 and 8 t ha–1 lime in both years even though all the limed plots produced significantly higher seed yields compared with plots not treated with lime in 2018 only. Data for 100 seed weight in Table 4 showed that in both years, each successive increment in lime rate significantly increased 100 seed weight.
| Table 3: Effects of phosphorus and lime on the number of nodules, number of pods per plant, number of unfilled pods and above-ground biomass of Arachis hypogaea | ||||||||
| 2018 | 2019 | |||||||
| Treatments | No. of nodules |
No. of pods |
No. of unfilled pods |
AGB |
No. of nodules |
No. of pods |
No. of unfilled pods |
AGB |
| Lime (L) | ||||||||
| L0 | 25.52 |
19.66 |
4.73 |
3.43 |
25.7 |
19.49 |
4.66 |
3.53 |
| L1 | 29.99 |
21.49 |
3.99 |
4.14 |
30.1 |
21.56 |
3.97 |
4.13 |
| L2 | 36.3 |
22.96 |
3.58 |
4.8 |
36.18 |
23.06 |
3.55 |
4.91 |
| L3 | 37.1 |
23.5 |
2.68 |
4.98 |
37.18 |
23.85 |
2.61 |
4.89 |
| LSD (0.05) | 2.69 |
0.49 |
0.42 |
1.13 |
6.79 |
0.55 |
0.14 |
1.62 |
| Phosphorus (P) | ||||||||
| P0 | 20.19 |
19.25 |
5.76 |
3.17 |
20.26 |
18.58 |
5.78 |
3.21 |
| P1 | 30.33 |
21.18 |
3.87 |
4.18 |
30.27 |
21.15 |
3.77 |
4.2 |
| P2 | 38.87 |
22.85 |
3.08 |
4.88 |
38.96 |
23.37 |
3.06 |
4.99 |
| P3 | 39.52 |
24.33 |
2.27 |
5.13 |
39.68 |
24.87 |
2.18 |
5.05 |
| LSD (0.05) | 2.69 |
0.49 |
0.42 |
1.13 |
6.79 |
0.55 |
0.14 |
1.62 |
| Interaction (L×P) | ||||||||
| L0P0 | 14.98 |
16.28 |
7.7 |
2.26 |
14.9 |
15.51 |
7.82 |
2.38 |
| L0P1 | 24.79 |
18.67 |
5.07 |
3.4 |
24.87 |
18.08 |
4.85 |
3.51 |
| L0P2 | 30.84 |
19.7 |
3.67 |
3.77 |
31.17 |
20.37 |
3.52 |
3.99 |
| L0P3 | 31.46 |
24 |
2.47 |
4.29 |
31.88 |
24.02 |
2.47 |
4.23 |
| L1P0 | 16.92 |
19.07 |
6.3 |
3 |
17.07 |
17.57 |
6.35 |
3.02 |
| L1P1 | 27.98 |
19.9 |
4 |
4.1 |
28.27 |
21.13 |
4 |
4.02 |
| L1P2 | 36.44 |
22.33 |
3.33 |
4.67 |
36.41 |
22.58 |
3.38 |
4.75 |
| L1P3 | 38.63 |
24.67 |
2.33 |
4.8 |
38.67 |
24.96 |
2.15 |
4.73 |
| L2P0 | 22.96 |
20.67 |
5.07 |
3.68 |
23 |
20.05 |
5.11 |
3.74 |
| L2P1 | 36.13 |
22.8 |
3.7 |
4.43 |
35.43 |
22.15 |
3.54 |
4.66 |
| L2P2 | 42.78 |
24.7 |
3.23 |
5.48 |
42.84 |
25.34 |
3.3 |
5.64 |
| L2P3 | 43.33 |
23.67 |
2.3 |
5.62 |
43.44 |
21.17 |
2.26 |
5.61 |
| L3P0 | 25.92 |
21 |
3.97 |
3.75 |
26.07 |
23.25 |
3.85 |
3.72 |
| L3P1 | 32.42 |
23.33 |
2.7 |
4.78 |
32.53 |
25.18 |
2.69 |
4.63 |
| L3P2 | 45.43 |
24.67 |
2.07 |
5.58 |
45.4 |
25.82 |
2.05 |
5.57 |
| L3P3 | 44.65 |
25 |
1.97 |
5.8 |
44.73 |
25.82 |
1.85 |
5.65 |
| LSD (0.05) | 5.39 |
0.98 |
NS |
NS |
NS |
1.1 |
0.28 |
NS |
| AGB: Above ground biomass, L0: 0, L1: 2, L2: 4 and L3: 8.0 t ha–1 of lime, P0: 0, P1: 25, P2: 50 and P3: 75 kg ha–1 of phosphorus fertilizer, LSD: Least significant different | ||||||||
| Table 4: Effects of phosphorus and lime on pods yield, seed yield, 100-seed weight, threshing percentage and harvest index of Arachis hypogaea | ||||||||||
| 2018 | 2019 | |||||||||
| Treatment | Pod yield | Seed yield |
100 seed wt. |
Thresh (%) |
HI |
Pod yield | Seed yield |
100 seed wt. |
Thresh (%) |
HI |
| Lime (L) | ||||||||||
| L0 | 2.28 |
1.15 |
42.98 |
68.58 |
0.33 |
2.26 |
1.26 |
43 |
68.19 |
0.35 |
| L1 | 2.77 |
1.37 |
44.28 |
75.61 |
0.33 |
2.76 |
1.37 |
43.8 |
74.02 |
0.33 |
| L2 | 3.15 |
1.65 |
45 |
78.78 |
0.34 |
3.2 |
1.71 |
44.27 |
77.12 |
0.34 |
| L3 | 3.26 |
1.72 |
45.97 |
82.03 |
0.34 |
3.3 |
1.68 |
45.41 |
79.56 |
0.32 |
| LSD (0.05) | 0.24 |
0.12 |
0.7 |
5.18 |
NS |
0.1 |
0.17 |
0.47 |
7.39 |
NS |
| Phosphorus (P) | ||||||||||
| P0 | 2.18 |
1 |
43.78 |
69.28 |
0.32 |
2.2 |
1.01 |
42.79 |
67.14 |
0.32 |
| P1 | 2.85 |
1.33 |
44.65 |
74.06 |
0.32 |
2.84 |
1.36 |
44.25 |
70.3 |
0.32 |
| P2 | 3.18 |
1.7 |
45.26 |
80.42 |
0.35 |
3.24 |
1.75 |
44.78 |
80.33 |
0.35 |
| P3 | 3.26 |
1.87 |
44.54 |
81.25 |
0.36 |
3.24 |
1.9 |
44.64 |
81.13 |
0.36 |
| LSD (0.05) | 0.24 |
0.12 |
0.7 |
5.18 |
0.12 |
0.1 |
0.17 |
0.47 |
7.39 |
NS |
| Interaction (L×P) | ||||||||||
| L0P0 | 1.56 |
0.7 |
41.17 |
65.03 |
0.31 |
1.57 |
0.81 |
41.2 |
63.73 |
0.34 |
| L0P1 | 2.37 |
1.03 |
43.47 |
67.27 |
0.31 |
2.31 |
1.2 |
43.71 |
67.37 |
0.34 |
| L0P2 | 2.5 |
1.27 |
43.3 |
70.67 |
0.34 |
2.54 |
1.45 |
43.16 |
70.42 |
0.36 |
| L0P3 | 2.7 |
1.59 |
44 |
71.33 |
0.37 |
2.63 |
1.59 |
43.92 |
71.25 |
0.37 |
| L1P0 | 1.93 |
1.06 |
44.27 |
68.83 |
0.35 |
1.95 |
1.07 |
42.53 |
67.33 |
0.35 |
| L1P1 | 2.83 |
1.27 |
44.53 |
74.8 |
0.31 |
2.77 |
1.25 |
44.04 |
69.93 |
0.31 |
| L1P2 | 3.17 |
1.5 |
44.33 |
79 |
0.32 |
3.23 |
1.52 |
44.42 |
79.17 |
0.32 |
| L1P3 | 3.13 |
1.67 |
44 |
79.8 |
0.35 |
3.1 |
1.63 |
44.21 |
79.66 |
0.34 |
| L2P0 | 2.59 |
1.08 |
44.1 |
70 |
0.3 |
2.66 |
1.08 |
43.13 |
67.88 |
0.29 |
| L2P1 | 3.03 |
1.39 |
44.73 |
75.47 |
0.32 |
3.11 |
1.55 |
44.33 |
71.28 |
0.33 |
| L2P2 | 3.5 |
1.98 |
46.5 |
84 |
0.36 |
3.57 |
2.07 |
44.6 |
83.79 |
0.37 |
| L2P3 | 3.47 |
2.15 |
44.67 |
85.67 |
0.38 |
3.47 |
2.14 |
45 |
85.54 |
0.38 |
| L3P0 | 2.62 |
1.13 |
45.6 |
73.23 |
0.3 |
2.64 |
1.08 |
44.32 |
69.62 |
0.29 |
| L3P1 | 3.17 |
1.62 |
45.87 |
78.7 |
0.34 |
3.18 |
1.45 |
44.93 |
72.62 |
0.31 |
| L3P2 | 3.53 |
2.05 |
46.9 |
88 |
0.37 |
3.63 |
1.95 |
46.94 |
87.94 |
0.35 |
| L3P3 | 3.73 |
2.07 |
45.5 |
88.2 |
0.36 |
3.75 |
1.9 |
45.45 |
88.05 |
0.34 |
| LSD (0.05) | NS |
Ns |
NS |
10.37 |
NS |
NS |
NS |
NS |
14.78 |
NS |
| HI: Harvest index, L0: 0, L1: 2, L2: 4 and L3: 8.0 t ha–1 of lime, P0: 0, P1: 25, P2: 50 and P3: 75 kg ha–1 of phosphorus fertilizer, LSD: Least significant different | ||||||||||
The threshing percentage as shown in Table 4 was significantly higher when 8 t ha–1 lime was applied compared to other rates of the application except at 4 t ha–1 in 2018 whereas in 2019, plots that were treated with lime had a threshing percentage increment in these order 8>4>2 t ha–1 lime but were statistically same. Also, zero lime application had the least threshing percentage except in 2019, where it was statistically at par with 1 t ha–1 application.
Phosphorus fertilizer application significantly influenced all yield and yield components in both years of study except harvest index in 2019 (Table 3 and 5). Application of 75 kg ha–1 P differed significantly from other rates of application in terms of the number of nodules produced except at 50 kg ha–1 P in both years. However, the zero application rate had the least number of nodules (Table 3). Data for the total number of pods per plant showed that each successive increment in the rate of P application had a corresponding significant increment in the total number of pods from zero to 75 kg P ha–1, whereas in both years, the number of unfilled pods decreased significantly with each successive increment in the lime rate with the highest lime rate having the least number of unfilled pods (Table 3).
The AGB in both years as shown in Table 3 indicates no significant difference among plots receiving 75, 50 and 25 kg P ha–1 and 75 kg ha–1 P only differed significantly when compared to zero application. Groundnut plant fertilized with 75 kg ha–1 P produced significantly higher pod yield than all other levels of the application except 50 kg ha–1 in 2018 and 2019 whereas those fertilized with 75 kg ha–1 P had significantly higher seed yields compared to all other rates of application in both years (Table 4). There was a significant increment in 100-seed weight for the successive increase in P rates in 2018 but in 2019, application of P increased yield in the descending order at 75>50>25 kg P ha–1 though statistically same. Zero P application had the least 100-seed weight in both years (Table 4). The effect of P application on the threshing percentage as shown in Table 4 shows that the 75 kg ha–1 P application was at par with 50 kg ha–1 P which in turn did not differ from 25 kg ha–1 P in 2018. In 2019, the order of increment in threshing (%) was 75>50>25>0 kg P ha–1, however, 75 kg ha–1 P was only significantly different when compared to the zero application rate. P application at 75 and 50 kg ha–1 P was statistically at par but significantly higher when compared to other levels of application.
Significant lime and phosphorus fertilizers interaction were observed on the number of nodules, the total number of pods per plant and threshing percentage in both years and the number of nodules in 2018 only (Table 3 and 4). Combined application of 8 t ha–1 Lime plus 50 kg ha–1 P produced the highest number of nodules but this was statistically the same when compared to those produced when 8 t ha–1 Lime plus 75 kg ha–1 P, 8 t ha–1 Lime plus 75 kg ha–1 P, 4 t ha–1 Lime plus 50 kg ha–1 P and 2 t ha–1 Lime and 75 kg ha–1 P were applied in 2018 respectively. However, the least number of nodules were produced in plots where neither Lime nor phosphorus was applied in both years. The total number of pods followed almost the same trend of increment in both years where plots treated with 8 t ha–1 Lime plus 75 kg ha–1 P produced the highest number of nodules but not significantly different from when 8 t ha–1 Lime plus 50 kg ha–1 P and 4 t ha–1 Lime plus 50 kg ha–1 P were applied respectively. Data recorded in Table 3 showed that plots that received neither lime nor P treatment had a significantly higher number of unfilled pods compared to any other treatment combinations. Relative to the control, threshing percentage did not differ significantly from other treatment combinations except when 8 t ha–1 lime plus 75 kg ha–1, 4 t ha–1 lime plus 75 kg ha–1, 8 t ha–1 lime plus 50 kg ha–1 and 4 t ha–1 lime plus 50 kg ha–1 were applied in 2018 and 2019 following a decreasing order in magnitude (Table 4).
Effects of lime and phosphorus application on the dry matter of Arachis hypogaea: The effect of lime and P on dry matter of plant in 2018 and 2019 are presented in Table 5. Dry matter content of groundnut treated with 8 t ha–1 lime increased significantly over that of control but was at par when compared to other lime rates in 2018 whereas, in 2019, 8 t ha–1 lime had significantly higher dry matter content compared to other rates of the application except for 4 t ha–1. Dry matter content of groundnut was statistically the same for all P treated plants but the respective P treated plants irrespective of the rate increased significantly over those in the control in 2018 whereas, in 2019, 75 kg ha–1 P had significantly higher dry matter content compared to other rates of the application except 50 kg ha–1.
| Table 5: Effects of phosphorus and lime on the dry weight of Arachis hypogaea | ||
| Dry matter | ||
| Treatments | 2018 |
2019 |
| Lime (L) | ||
| L0 | 29.68 |
30.94 |
| L1 | 32.34 |
33.09 |
| L2 | 34.5 |
36.36 |
| L3 | 36.47 |
37.12 |
| LSD (0.05) | 5.42 |
2.36 |
| Phosphorus (P) | ||
| P0 | 24.72 |
25.57 |
| P1 | 30.73 |
31.57 |
| P2 | 37.74 |
39.64 |
| P3 | 39.81 |
40.74 |
| LSD (0.05) | 5.42 |
2.36 |
| Interaction (L×P) | ||
| L0P0 | 21.68 |
23.35 |
| L0P1 | 26.88 |
27.55 |
| L0P2 | 34.2 |
34.87 |
| L0P3 | 35.97 |
38.01 |
| L1P0 | 23.78 |
24.47 |
| L1P1 | 29.59 |
30.26 |
| L1P2 | 36.52 |
38.17 |
| L1P3 | 39.48 |
39.48 |
| L2P0 | 25.49 |
26.07 |
| L2P1 | 32.13 |
33.73 |
| L2P2 | 39.17 |
42.9 |
| L2P3 | 41.2 |
42.74 |
| L3P0 | 27.92 |
28.39 |
| L3P1 | 34.3 |
34.73 |
| L3P2 | 41.06 |
42.63 |
| L3P3 | 42.58 |
42.74 |
| LSD (0.05) | NS |
4.73 |
| L0: 0, L1: 2, L2: 4 and L3: 8.0 t ha–1 of lime, P0: 0, P1: 25, P2: 50 and P3: 75 kg ha–1 of phosphorus fertilizer, LSD: Least significant different | ||
The zero P application had the least dry matter content (Table 5). Significant interactions between lime and P were only obtained in dry matter for the 2019 planting season.
DISCUSSION
The soils were strongly acidic to moderately acidic with a pH of 5.4 and 5.59 for the 2018 and 2019 cropping years, respectively. The observed exchangeable cations (Ca, Mg and K) were all low. Similarly, the total nitrogen and ECEC were equally low. Available P and BS were high for both cropping seasons. The low pH, low exchangeable cations and high P content are characteristics that typify the ultisols, such values have also been observed by Akpan et al.14 and Afu et al.6 in their result. The low levels of soil bases as well as low soil pH, could be a result of crop removal and leaching losses. These soils need special management techniques for sustainable crop production including organic manuring, mulching, liming among others6.
Plants that received 4-8 t ha–1 lime tended to be taller, produced more branches and leaves besides having larger leaves. Similar observations were made by Li et al.27 while working on several crop species. This increase in growth could be attributed to the enhanced availability of essential elements resulting from the favourable pH created by the application of lime. The growth of groundnut including plant height, number of branches, number of leaves, leaf expansion as well as the production of viable root nodules were enhanced by the application of lime relative to the control. Lime is known to react with soil water producing Ca2+ and OH– which displaces Al3+ and H+ ions from the soil adsorption sites resulting in increased soil pH values and the unlocking of fixed essential nutrients for crop growth has also been observed by Fageria et al.28. Kisinyo et al.16 and Verdes et al.29 also observed enhanced growth of soybeans due to improved availability of Mg, Ca and Mo as a result of liming. Liming also ameliorates the effects of high concentrations of Al3+, H+ and Mn2+ in acidic soils which causes root injuries and reduced uptake of some important nutrients as also observes by Zheng8. Apart from the improvement in the release of P and other essential nutrients, liming promotes microbial activities and besides aid in the breakdown of organic matter which adds more N and nutrients to enhance plant growth. The result is in line with the observations of Fageria et al.28 and Fonara et al.18.
The yield and yield attributes except harvest index were greatly enhanced by lime application, the number of pods, pod yield, seed yield as well as 100-seed yield and threshing percentage values increased considerably with the application of 4-8 t ha–1 lime while the zero application rate had the least of these values. This implies that highly acidic soils can be made more productive by liming the soil with 4-8 t ha–1 lime. The boosting in yield of groundnut could be attributed to the significant reduction in the number of unfilled pods due to liming. The improvement in P nutrition as a direct result of liming is known to promote the development of stronger roots and nodules as well as stimulate pod growth and pod filling capacity of legumes17. The improvement in growth including an overall increase in the number of branches, leaves/leaf area expansion due to the lime application could indirectly increase the photosynthetic capacity of groundnut and contributed greatly to an increase in pod and seed yield. Also, improved nodulation and microbial decomposition of organic materials in limed soils are additional sources of supply of essential nutrients that could have boosted the yield of groundnut16,18,28,29. Several other researchers have indicated positive effects of liming on crop growth and yield20-22,24. The application of 4 t ha–1 lime in most cases was as good as the application of 8 t ha–1 lime implying that it may not be economically wise to exceed the application rate of 4 t ha–1. Haynes and Naidu30 had earlier observed that though the liming of acid sands is needful for improved crop performance, the addition of an excess of it would either be wasteful or detrimental to the crop.
From this study, the application of P fertilizer had clear positive effects on the vegetative growth of groundnut. Phosphorus applied at a rate ranging from 50-75 kg ha–1 boosted plant height, leaf production and expansion as well as branching and nodule development. Similarly, pod growth, pod and seed yields and accompanying attributes such as 100-seed weight, threshing percentage and dry matter contents were significantly enhanced in plots treated with P relative to the control. These assertions could broadly be linked to the essential roles of P in photosynthesis, the formation of healthy roots and therefore nodules, nitrogen fixation as well as dry matter formation. Apart from the direct involvement of P in photosynthesis, the enhanced nodulation and N fixation to the soil boosted N supply which stimulated the growth of more branches, leaves which indirectly increased the amount of photosynthates production in groundnut hence high pod and seed yield. Phosphorus fertilizer also decreased appreciably the number of empty pods, further enhancing the seed yield and other yield attributes. The increase in overall plant growth and N concentration in response to increasing soil P supply have already been reported in soybeans31 and groundnut32. It was further observed that applying P above 50 kg ha–1 did not give any reasonable increment in pod or seed yield. Yakubu et al.33 had earlier reported that application of P as low as 20-40 kg ha–1 can be improved nodulation, N accumulation and grain yield in legumes in the Guinea savanna region but over-supply of P may reduce growth and nodulation.
A significant interaction between lime and P was observed in this study. The tallest plants with the highest number of leaves were produced by combined application of 8 t ha–1 lime plus either 75 or 50 kg ha–1 P and 4 t ha–1 lime alongside 75 kg ha–1 P. Similarly, yield and yield attributing factors were enhanced when 8 t ha–1 lime were jointly applied with 20-80 kg ha–1 P and remain statistically same even at the application of 2 t ha–1 lime plus 75 kg ha–1 P. This implies that it is possible to achieve higher yield by applying reduced but combined quantities of both lime and P or by jointly applying a maximum quantity of one and a minimal quantity of the other than applying the maximum quantities of either of them. This might be explained by the fact that liming has a profound effect on the availability and recovery efficiency of P besides its effects on the dynamics of other nutrients25,34. Liming also decreases the adsorption of P to the soil constituents thus increasing the supply of P for crops’ use bearing in mind that over 80% of applied P becomes unusable to crops as a result of this adsorption or its precipitation principally by Al and Fe compounds in acid soils as reported by Griesler et al.5.
Acidic soils are known to create production problems by limiting the availability of some essential plant nutrients and increasing that of the soil toxic elements and this mostly results in poor growth of a plant and reduced yield. Despite all these constraints, this study found out that with the application of lime, the optimum yield was still possible for groundnut. The present study has demonstrated that yield and yield attributing factors could be enhanced when 8 t ha–1 of lime were jointly applied with 20-80 kg ha–1 P. This implies that acidic soils should be limed to improve the availability of plant growth nutrients before such plant can be grown on it to achieve maximum yield. Additionally, the application of phosphorus fertilizer also promoted vegetative growth and yield of the groundnut. It is therefore recommended that farmers should use lime and phosphorus fertilizer for plant production under acidic conditions to obtain a higher yield.
The study was only limited to assessing the effect of P and lime on the growth and yield performance of groundnut, however, the post-harvest effect on soil properties was not considered. Also, the major limitation of the study was drudgery associated with manual land preparation.
CONCLUSION
Combining lime and P fertilizer was observed to increased groundnut growth and yield. The tallest plants with the highest number of leaves could be produced by combining 8 t ha–1 lime plus either 75-50 kg ha–1 P and 4 t ha–1 lime alongside 75 kg ha–1 P. Similarly, yield and yield attributing factors could be enhanced when 8 t ha–1 lime were jointly applied with 20-80 kg ha–1 P. This study found out that application of 4 t ha–1 lime in most cases was as good as the application of 8 t ha–1 lime, implying that it may not be economically wise to exceed application rate of 4 t ha–1 to maximize crop production cost while maximizing yield.
SIGNIFICANCE STATEMENT
This research work has shown that adequate yield improvement in groundnut may be achieved in acid sand Ultisol through the application of mineral phosphorus in addition to lime. Combining lime and P fertilizer was observed to increased groundnut growth and yield. The tallest plants with the highest number of leaves produced when combining 8 t ha–1 lime plus either 75 or 50 kg ha–1 P and 4 t ha–1 lime alongside 75 kg ha–1 P. The application of 4 t ha–1 of lime in most cases gave similar agronomic and yield performance as the application of 8 t ha–1 lime, hence, it may not be economically wise to exceed the application rate of 4 t ha–1 to minimized crop production cost, while maximizing yield. Hence, the result of this study will be beneficial to agronomists, growers and researchers at large looking for cost-effective means of solving soil acidity problems as well as means of maximizing crop yield.