Research Article
Evaluation of Ground Phosphate Rocks for Growth and Yield of Maize (Zea mays) and Soybean (Glycine max) on a Tropical Alfisol in Nigeria
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Emmanuel Teboh
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Gabriel Olufemi Obigbesan
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Phosphorus (P) is crucial for optimum growth and yield of leguminous crops and cereals. Its deficiency in tropical soils is considered one of the main constraints to food production in large areas of farmland of sub humid and semi arid Africa[1,2]. According to Adediran and Sobulo[3], P-fertilization is a vital factor in agricultural development in Africa.
The use of inorganic P sources has been limited by its acquisition and distribution to farmers as a result of high cost and poor distribution network[4]; hence the need to look for alternative or supplementary and cheaper sources. The direct use of sparingly soluble, ground Rock Phosphate (RP) as an alternative to the imported and expensive more soluble P fertilizers has been reported[5]. RP are known to be less effective than the super phosphates due to their limited solubility[6]. They provide a gradual release of plant available P and a residual effect for several years[7].
Throughout the world, wheat, rice and maize are produced in greater quantities than any other crop. Of these crops, maize has the highest average yield of 3.7 t ha-1[8]. Maize is used for human consumption, animal feed and for industrial purpose[9]. Soybean is significant as a world crop due to its high protein content and high quality oil. It is a food crop of great potential in the improvement of diet of millions of people in developing countries[10].
Information on the Right Time of RP application and the best RP source for maize and soybean production are not substantial. Besides, not much research has been done on the residual effect of RP in soybean production. As such, the present study sought to determine the best time of RP application, the best RP source in maize and soybean production and evaluate the residual effect of RP on soybean production.
Three field experiments were carried out at the Rockefeller experimental plot of the Teaching and Research Farm, University of Ibadan, Nigeria, with an Ibadan soil series[11] classified as a haplic luvisol/arenic haplustalf by the FAO/UNESCO classification[12]. The soil textural class was loamy sand and Ibadan lies in the northern limit of the lowland forest zone of western Nigeria on latitudes 7°43N and longitudes 3°90E, with an annual rainfall of about 1220 mm having a bimodal distribution[13].
The field plot (30x20 m = 600 m2) was divided into three equal blocks (replicates) of 30x 6 m with inter-block spacing of 1 m. Each replicate was divided into 20 equal plots (6x1 m) with interplot spacing of 0.5 m, giving a total of 60 plots. The experiments were split-plot with Randomized Complete Block Design involving two factors:
• | Four P application times (one week before planting, 1 WBP; at planting, AP; one week after planting, 1 WAP and 2 WAP) as sub plot factor |
• | Five P sources (ground rock phosphate of crystallizer, Cryst; Ogun rock phosphate, ORP; Sokoto rock phosphate, SRP; single super phosphate, SSP, as reference P fertilizer source and control, no phosphate addition) as main plot factor. |
Besides the control (0 kg P2O5 ha-1), an optimum P level of 50 kg P2O5 ha-1 was used. Before the commencement of each of the experiments, soil samples (five cores per plot) were collected for physico-chemical analysis.
Early maturing maize (Zea mays variety Acr. 89 DMR-ESRW) was used as test crop for the first experiment spanning between August and October 1999. Planting was done on the flat. Prior to planting, the first treatment of 1 WBP was applied. Thereafter, the other treatments of AP, 1 WAP and 2 WAP were respectively applied. Plant spacing was 60x30 cm with one plant per stand, giving a plant population of 55,555 plants ha-1. Nitrogen was uniformly applied as urea (90 kg ha-1) at 2 WAP and 60 kg ha-1 at 6 WAP. Potassium as muriate of potash was also applied at a rate of 60 kg ha-1 at 2 WAP.
The second and third experiments, carried out in 2000 and 2001, respectively made use of an early maturing non-inoculated promiscuous soybean [Glycine max (L) Merr.] variety TGX 1845 1D. The experimental design remained the same as in the first experiment but while in the second experiment there was P application, the third experiment was to test for the residual effect of the previously applied P. Nitrogen was uniformly applied (as urea) at a rate of 60 kg ha-1 at 2 WAP in both experiments. The soybean was planted at a spacing of 60x5 cm, giving a plant population of 333,333 plants ha-1.
The nutrient status of the soil prior to the first experiment (Table 1) showed that available P value was high compared with the critical value of 8-10 mg kg-1[14].
Table 1: | Pre-planting soil analysis of surface (0-15 cm) soil samples for the three experiments |
Table 2: | Rainfall data (mm) during the three field experiments. |
Source: International Institute of Tropical Agriculture (IITA) Weather Station, Ibadan, Nigeria |
From the first to the start of the second experiment available P and soil pH reduced. This could be attributed to the fact that it was about 13 months after the first experiment that the second experiment was carried out. Several processes (e.g., nutrient fixation) must have taken place in the soil that must have led to P unavailability. There were increases in available P, pH and exchangeable cations from the commencement of experiment 2 to experiment 3. These increases could be due to the liming effect of RP[15] and its ability to contribute to the increase in the soil available P[16].
The response of maize to different times of phosphorus application: The growth parameters (plant height, stem girth, number of leaves and leaf area) were highest when the P fertilizers were applied 2 WAP (Table 3-5).
Table 6 shows that the effect of the different times of P application on maize grain yield was variable. However, Cryst and ORP were most effective when applied 1WAP. On the contrary, SRP and SSP performed best when applied 2 WAP and AP, respectively. These fall in line with the recommendations of Adepetu[17]. He reported that P application AP and 2 WAP are the most favourable times of application.
Table 3: | Effect of time of phosphorus fertilizer application on height (cm) of maize and soybean at successive growth periods |
* Means in the same column followed by the same letter are not significantly different at p=0.05 (Duncans Multiple Range Test); WBP = Week before planting; AP = At planting; WAP = Week after planting |
Table 4: | The effect of time of phosphorus fertilizer application on number of leaves of maize and soybean at successive growth periods. |
* Means in the same column followed by the same letter are not significantly different at p=0.05 (Duncans Multiple Range Test); WBP = Week before planting; AP = At planting; WAP = Week after planting |
The effect of the different times of phosphorus application on soybean growth: From results of the effect of times of P application on the growth parameters (plant height, leaf area and number of leaves) of soybean (Table 3-5), it is evident that P application at 1 WBP was the most appropriate time irrespective of the P source. This is in accordance with the report by Sinclair et al.[18] and Wendt and Jones[19]. These reports recommended that P should be applied before planting so as to allow for solubilization to take place for easy plant uptake of the added P.
ORP, SRP and SSP led to highest soybean seed yield when applied 1 WAP (Table 6). Cryst, however, produced the highest seed yield when applied 1 WAP as recommended by Sinclair et al.[18].
The very low seed yield recorded is attributable to the fact that the crop was planted late in the season (September) and the drought affected the reproductive stage (Table 2).
Table 5: | The effect of time of phosphorus fertilizer application on leaf area (cm2) of maize and soybean at successive growth period |
* Means in the same column followed by the same letter are not significantly different at p=0.05 (Duncans Multiple Range Test); WBP = Week before planting; AP = At planting; WAP = Week after planting |
Table 6: | Grain yields of maize and soybean in response to phosphorus fertilizer sources applied at different times in the first and second cropping |
*Values followed by the same letters are not significantly different at p=0.05 (Duncan's Multiple Range Test) WBP = Week before planting; AP = At planting; WAP = Week after planting |
Board and Harville[20] as well as Linkemer et al.[21] explained that water deficit leads to greatest decreases in soybean seed yield by reducing branch seed yield. It reduces branch growth[22].
The response of maize and soybean to different phosphorus sources: Table 7 shows the effect of the different P sources on maize and soybean production. SSP had the best effect on maize grain yield (2.31 t ha-1), followed by Cryst (1.89 t ha-1), ORP (1.94 t ha-1) and SRP (1.80 t ha-1). However, in soybean production, ORP performed best (Table 7). This performance by ORP was only significantly higher than the yield for the control. The good performance of ORP as a source of P for soybean production was due to its reported good reactivity in soils with pH greater than 6[23].
Table 7: | Grain yields of maize and soybean in response to different phosphorus fertilizer sources in the first and second cropping, respectively |
*Values followed by the same letters are not significantly different at p=0.05 (Duncan's Multiple Range Test) |
On the other hand, crystallizers performance could be attributed to its having most of the micronutrients necessary for plant growth.
The residual effect of phosphorus sources on soybean yield: The seed yield varied between 1116.7 and 1333.3 kg ha-1 (Table 8).
Table 8: | Residual effects of the phosphate fertilizer sources on the seed yield of soybean |
*Values followed by the same letters are not significantly different at p=0.05 (Duncan's Multiple Range Test) |
Cryst had the best residual seed yield of 1333.3 kg ha-1, though it was not significantly higher than those of the other P sources. It was closely followed by ORP with 1166.7 kg ha-1, while both SRP and SSP gave 1150.0 kg ha-1 each. The higher residual seed yield produced by Cryst could be attributed to its enhancement of soil nutrient balance since it acts as a useful source of some micronutrients e.g., Fe, Cu etc.[23].
Any of the RP sources (Cryst, ORP and SRP) could be used as a source of P for the growth of both maize and soybean. Likewise, any of the four times of applications (1 WBP, AP, 1 WAP and 2 WAP) is suitable for a good yield of maize or soybean. Considering the insignificance of the effect of the residual P of the RP sources, any of them could be relied upon to provide good residual effect on the yield of soybean.
The Senate Research Grant of University of Ibadan, Nigeria funded the research.