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Effects of Rates and Split Application of Compound NPK Fertilizer on the Growth and Yield of Three Amaranthus Species in Nigeria Guinea Savanna



S.O. Alonge , F.O. Alonge , S.P. Bako , J.D. Olarewaju and O.B. Adeniji
 
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ABSTRACT

Field trials were conducted at two sites in Ahmadu Bello University, Samaru-Zaria, Nigeria, to determine the effect of five rates (0, 125, 2501, 2502 and 500 kg ha-1) of compound fertilizer (NPK 27:13:13) on the growth (root and shoot dry weight) and grain yield of three Amaranthus species. The Amaranthus species include: A. hybridus, A. spinosus and A. hybridus var. cruentus. The plants were sampled weekly between 4 and 7 Weeks After Planting (WAP) and the second dose of the fertilizer (for 125 and 2502 kg ha-1) was applied at 5 WAP. The best growth in the Amaranthus species resulted from 500 kg ha-1 NPK treatment at 4 and 5 WAP and from 2502 kg ha-1 NPK treatment at 6 and 7 WAP. The 2501 kg ha-1 NPK application also produced slightly higher values in growth parameters than 125 kg ha-1 at 4 and 5 WAP, but this situation was reversed at 6 and 7 WAP. The overall data showed that, 2502 kg ha-1 NPK treatment produced higher shoot growth and grain yield than the other treatments. Amaranthus hybridus had the highest shoot growth and total dry weight ha-1 than the other species. Amaranthus hybridus var. cruentus also produced the highest total grain weight per hectare than the other species. This study showed that, the split in contrast to sole application of NPK fertilizer rates can be of greater economic benefit in Amaranthus production.

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S.O. Alonge , F.O. Alonge , S.P. Bako , J.D. Olarewaju and O.B. Adeniji , 2007. Effects of Rates and Split Application of Compound NPK Fertilizer on the Growth and Yield of Three Amaranthus Species in Nigeria Guinea Savanna. Asian Journal of Plant Sciences, 6: 906-912.

DOI: 10.3923/ajps.2007.906.912

URL: https://scialert.net/abstract/?doi=ajps.2007.906.912

INTRODUCTION

Amaranthus is a genus of the family Amaranthaceae. Amaranthus species are the most commonly grown leafy vegetable of the lowland tropics in Asia and Africa (Schippers, 2000). Cultivation of the various Amaranthus species is acquiring increasing importance in Nigeria and other parts of African continent where the available species are grown for their leaves. According to Becker and Saunders (1984) animals eat more of those with thorns (A. spinosus). Amaranthus species can grow up to 100 cm high with colour ranging from green to purplish or pinkish Amaranthus requires a fertile soil well supplied with organic matter for good productivity. Like any grain crop, Amaranthus responds to good soil fertility. Nitrogen has proven to be the limiting soil nutrient in most situations (Weber, 1989) which has led to a small number of studies on the effect of nitrogen fertilizer on Amaranthus especially in U.S.A. For instance, in a study in Arkansas, with one grain cultivar and one vegetable cultivar, there was a seed yield response to nitrogen fertilizer in the one environment tested and also observed that the seed weight increased in response to nitrogen rate (Markus, 1990). Myers (1998) also reported that, addition of N fertilizer caused several significant responses in the growth and development of grain Amaranthus. Nitrogen fertilizer increased grain yield for all three cultivars tested in all three environments. Studies by Tindall et al. (1987) showed that, application of 168 kg N ha-1, 112 kg P2O5 ha-1 and 168 kg K2O ha-1 is sufficient for proper growth and development of Amaranthus. They further stated that the nitrogen should be applied 2-3 times in split doses.

According to Schippers (2000) there are no exact data on yields for the various African species of Amaranthus. Good productivity in Amaranthus however requires optimum conditions which include judicious use of inputs such as fertilizers. Application of the right fertilizer in adequate amounts and at appropriate times during crop growth will significantly increase Amaranthus yield and consequently economic returns to farmers.

In Nigeria, fertilizer being costly and sometimes scarce can make farmers not apply enough for good growth. This is coupled with the fact that, research work is generally scarce on fertilizer requirement of Amaranthus in Nigeria and particularly in the guinea savanna ecological zone. Also, the NPK 27:13:13 fertilizer used in this study is fairly new in the market (the most common type being NPK 15:15:15) although being used for cereal cultivation which requires high nitrogen levels, just as it has been reported for Amaranthus (Maerere et al., 2001). There is therefore the need to investigate the response of some of the available Amaranthus species to this new compound fertilizer as a process to determine the required application rate under the Guinea savanna ecological conditions in this country. Thereby the minimum application level of this fertilizer to enhance good growth and grain yield in Amaranthus species can be determined. It is being hypothesized that all the applied rates will produce good growth and the species are similar in their response to fertilizer rates.

This study was therefore conducted to investigate the effects of compound fertilizer (NPK 27:13:13) rates and split application of it on the vegetative growth and grain yield of three Amaranthus species. This study will provide information on the response of the species to and the rate of the fertilizer suited for the growth of the Amaranthus species. This can produce an information for reduced-input approach in Amaranthus cultivation.

MATERIALS AND METHODS

The investigation was carried out in the Botanical garden (Site I) and Area G (Site II), Ahmadu Bello University, Zaria (Latitude 11° 111 N, longitude 7° 381 E and 686 m above sea level) Nigeria. This lies within the northern limit of the Guinea savanna ecological zone. The soil is a well drained leached ferruginous sandy loam overlying rocks of the Pre-Cambrian basement complex (Tomlinson, 1965) and regarded as an inceptisol according to the USDA system of soil classification (Harpstead, 1973). The climate is characterized by a well-defined wet season and the location receives an average annual rainfall of 1100 mm, occurring almost entirely between May and September.

Description of experimental materials: The three species of Amaranthus used for the investigation include: Amaranthus hybridus, Amaranthus spinosus and Amaranthus hybridus var. cruentus. The seeds of Amaranthus hybridus and A. spinosus were collected from local farmlands and uncultivated lands in Samaru-Zaria, Kaduna State, Nigeria, while that of A. hybridus var. cruentus was collected from farmlands in Ijebu-Jesa, Osun State, Nigeria.

Amaranthus hybridus: This is the improved species of Amaranthus. It has a wide distribution across the country. It usually occurs as the red type (red stems, leaves and flowers) and the green type (commonly called the white type). The green type was used for the investigation.

Amaranthus spinosus: This Amaranthus species which is considered as a weed in parts of Nigeria is eaten as vegetable in some parts of Delta and Edo states, Nigeria. It is also a very good fodder for cattle and goats. It usually produces a pair of thorns at each node from where it also develops branches from the axillary buds. It is widely distributed across the country. Some of the varieties have reddish stem and greenish leaves while others have greenish stems and leaves. The latter type was used for this experiment.

Amaranthus hybridusvar.cruentus:This Amaranthus species is very common in the South Western part of the country. It adapts more to areas of fertile and moist soils of south western Nigeria, where it is commonly grown without fertilizer application and is eaten as a preferred vegetable to other species of Amaranthus in the region. Its stems, petioles and lower part of the midrib are reddish in colour. It develops branches and flowers from all its nodes.

Planting procedure: The land was cleared manually after which West African hoe was used to make 1 m2 square beds with a space of 50 cm between beds. The physico-chemical properties of the soil in the experimental sites are presented in Table 1. About 150 seeds each of the three Amaranthus species were each mixed with about 50 g of sand and broadcast evenly on each bed. Immediately after sowing, NPK 27:13:13 fertilizer was applied at 0, 125 (twice), 2501, 2502 (twice) and 500 kg ha-1, an equivalent of 0, 33.75 (twice), 67.50, 67.50 (twice) and 135 kg N ha-1, respectively. The second dose for those that received split application was applied at 5 Weeks After Planting (WAP) to the appropriate beds. The treatments were replicated three times and laid out in a completely randomized design. The seedlings were thinned to 50 plants per bed at 3 WAP.

Table 1: Physical and chemical properties of soil at the experimental sites

Sampling: The weekly sampling of Amaranthus seedlings for growth parameters was from 4-7 WAP. On each sampling date, 6 plants were randomly uprooted carefully from each of the replicated plots of each treatment and carried in labeled polythene bags to the laboratory where they were washed and drained for the determination of the growth parameters.

Fresh and dry matter production: After the above each plant was separated into root and shoot with knife. The fresh weights of the root and shoot of each plant were determined separately on a Metler balance. Each plant part was put in labeled envelope and placed in an oven maintained at 70C till a constant weight was obtained, after which the dry weight of each plant part was measured. Afterward, the remaining plants on each plot were allowed to flower, mature their grains and dry up. The plants dry weight at harvest, grain yield and yield components were then determined as follows:

Total plant dry weight at harvest: All the dry plants on each plot at the end of the experiment were uprooted and packaged in labeled envelopes. Each of them was weighed on Metler balance and the weight recorded.

Grain yield: All the seeds on the dry plant from each plot was threshed, winnowed and weighed to obtain grain yield production per plot.

All the data collected were subjected to ANOVA (analysis of variance) using Genstat (Anonymous, 1980). Significant difference between treatments and species means were then compared using Duncan Multiple Range Test (DMRT).

RESULTS
Root Dry Weight (RDW): The effect of NPK fertilizer treatments on the RDW of each Amaranthus species was presented in Table 2. Generally, most NPK treatments resulted in similar RDW in each Amaranthus species at 4 WAP in each site. With the exception of A. spinosus in site II, the control treatment tended to produce the least RDW in each Amaranthus species on most sampling dates in site I and site II.

A. hybridus: At both sites A. hybridus had the highest root dry weight under 500 kg ha-1 NPK treatment at 5 and 6 WAP, while it was due to 2502 kg ha-1 NPK treatment at 7 WAP.

Table 2: Effect of NPK fertilizer rates on the root dry weight (g) of Amaranthus species grown in two sites (I and II) differing in physico-chemical properties
Figures followed by the same letter(s) in each column in each site are not significantly different (p = 0.05), using DMRT. WAP-Weeks After Planting; **Significant at 1%; NS = Not Significant at 5%

In site I, the highest root dry weight due to 500 kg ha-1 NPK treatment was only comparable with that from 2502 kg ha-1 NPK treatment at 5 WAP, while it was significantly higher than that of the other treatments at 6 WAP. At 7 WAP, the highest RDW in A. hybridus due to 2502 kg ha-1 NPK treatment was only significantly higher than the least due to the control treatment (p = 0.05) in each site.

A. hybridus var. cruentus: The 500 kg ha-1 NPK treatment produced the highest RDW in A. hybridus var. cruentus at 5 and 6 WAP in site I and at 5, 6 and 7 WAP in site II. The 2502 kg ha-1 NPK treatment produced the highest RDW in A. hybridus var. cruentus only at 7 WAP in site I.

A. spinosus: The 500 kg ha-1 NPK treatment produced the highest RDW in A. spinosus at 5 WAP in site I and at 4, 5 and 6 WAP in site II which was only significantly higher than that of the control and 125 kg ha-1 NPK treatments. On the other hand, 2502 kg ha-1 NPK treatment produced the highest RDW at 6 and 7 WAP in site I and at 7 WAP in site II which was only significantly higher than that of the other treatments (except 500 kg ha-1 NPK treatment).

Irrespective of sampling dates and species the RDW due to 2502 and 500 kg ha-1 NPK was comparable in each site and in the overall combined data and significantly higher than that due to the other treatments (Table 2). The least root dry weight due to the control treatment was comparable with that due to 125 kg ha-1 NPK in site II but significantly lower than that of all the other treatments in site I. Amaranthus hybridus var. cruentus had the least RDW among the species in each site and in the overall combined data, but this was only significant in site I and in the overall combined data (p = 0.05). The combined data also showed that irrespective of site and NPK treatments the RDW produced was in the order: A. spinosus A. hybridus A. hybridus var. cruentus.

Shoot Dry Weight (SDW): The effect of NPK fertilizer treatments on the SDW of each Amaranthus species was presented in Table 3. Generally, the control treatment produced the lowest SDW in each Amaranthus species on most sampling dates at both sites (Table 3). With the exception of A. hybridus var. cruentus, the Amaranthus species had the best shoot growth under 2502 kg ha-1 NPK treatment.

Table 3: Effect of NPK fertilizer rates on the shoot dry weight (g) of Amaranthus species grown in two sites (I and II) differing in physico-chemical properties
Figures followed by the same letter(s) in each column in each site are not significantly different (p = 0.05), using DMRT. WAP-Weeks After Planting; **Significant at 1%; NS = Not Significant at 5%

A. hybridus: The highest SDW in A. hybridus was produced by 2502 kg ha-1 NPK treatment at 4, 5 and 7 WAP in site I and at 4, 6 and 7 WAP in site II. This was comparable with that produced by 500 kg ha-1 at 4 WAP, 125 and 500 kg ha-1 NPK treatments at 5 and 7 WAP in site I. The data showed that, the SDW in each of the species due to 500 kg ha-1 NPK treatment tended to be comparable to the highest by 2502 kg ha-1 NPK treatment.

A. hybridus var. cruentus: The highest SDW in A. hybridus var. cruentus was by 500 kg ha-1 NPK treatment at 4 and 5 WAP at site I and at 4-6 WAP at site II (Table 3). The 2502 kg ha-1 NPK treatment produced the highest SDW in A. hybridus var. cruentus at 7 WAP at both sites. There was a comparable SDW in A. hybridus var. cruentus produced by 125 kg ha-1 and the control treatments and between 2502 and 500 kg ha-1 NPK treatments on most of the sampling dates at the two sites.

A. spinosus:On the other hand, the highest SDW in A. spinosus was due to 2502 kg ha-1 NPK treatment at 4-7 WAP in site I and at 6-7 WAP in site II (Table 3). The data tended to show a comparable SDW produced by 2501, 2502 and 500 kg ha-1 NPK treatments, on most of the sampling dates.

The overall combined ANOVA of the data showed that, irrespective of Amaranthus species and sites, 2502 kg ha-1 NPK treatment produced the highest SDW in Amaranthus species which was significantly higher than that of the other treatments, this was followed by that of 500 kg ha-1 NPK treatment with the least from the control treatment. The data also showed that A. hybridus produced significantly higher SDW than the other species which in turn had comparable SDW.

Total plant dry weight ha-1: The effect of NPK fertilizer treatments on the total plant dry weight ha-1 of each Amaranthus species was presented in Table 4. In each Amaranthus species, the 2502 kg ha-1 NPK treatment produced the highest total plant dry weight ha-1, which was significantly higher than that of the other treatments. On the other hand, the control treatment produced the least total plant dry weight ha-1 in each Amaranthus species (Table 4). The effect of 500, 2501 and 125 kg ha-1 NPK treatments on the total plant dry weight ha-1 of each Amaranthus species were found comparable and in between the above extremes (highest and lowest).

The combined ANOVA of the data showed that, 2502 kg ha-1 NPK treatment resulted in significantly higher total plants dry weight ha-1 in Amaranthus species than the other treatments which in turn (except the lowest from the control) produced similar total plant dry weight ha-1. The data also showed that the total plant dry weight ha-1 in Amaranthus species was in the order: A. spinosus.>A. hybridus > A. hybridus var. cruentus

Table 4: Effect of NPK fertilizer rates on the total plant dry weight ha-1 of Amaranthus species in site I
Figures followed by the same letter(s) in each column in each site are not significantly different (p = 0.05), using DMRT. **Significant at 1%

Table 5: Effect of NPK fertilizer rates on the total seed weight ha-1 of Amaranthus species in site I
Figures followed by the same letter(s) in each column in each site are not significantly different (p = 0.05), using DMRT. **Significant at 1%; NS = Not Significant at 5%

Total seed weight/ha: The effect of NPK fertilizer treatments on the total seed weight/ha of each Amaranthus species was presented in Table 5. The 2502 kg ha-1 NPK treatment resulted in the highest total seed weight/ha in each Amaranthus species and this was significantly higher than that due to the other treatments in most species. With the exception of A. hybridus, the application of NPK fertilizer at 500, 2501 and 125 kg ha-1 NPK treatments resulted in higher total seed weight ha-1 than that of the control which produced the least in each species. The seed weight from plants under 125 kg ha-1 NPK treatment was however slightly higher than that of 2501 and 500 kg ha-1 treatments in A. spinosus and A. hybridus var. cruentus.

The combined ANOVA of the data showed that, 2502 kg ha-1 NPK treatment resulted in significantly higher total seed weight ha-1 in Amaranthus species than the other treatments. This was followed by that due to 125 kg ha-1 NPK treatment, while the least total seed weight ha-1 due to the control treatment, was significantly lower than that of all the treatments. The data also showed that, the total seed weight ha-1 produced by Amaranthus species was in the order: A. hybridus var. cruentus > A. hydridus > A. spinosus.

In summary, the control treatment resulted in lower growth and grain yield values than all the other NPK treatments. Application of NPK at 2501, 2502 and 500 kg ha-1 tended to produce comparable root growth and SDW at 4 WAP. Application of NPK at 500 kg ha-1 produced the highest values in most of the growth parameters at 4 and 5 WAP. The second dose application of NPK (125 and 2502 kg ha-1) at 5 WAP stimulated growth of Amaranthus species at 6 and 7 WAP. The overall data showed that, 2502 kg ha-1 NPK treatment produced higher values in the shoot growth and grain yield parameters than the other treatments. However, 2502 and 500 kg ha-1 NPK treatments produced comparable values for root growth parameters.

DISCUSSION

Amaranthus species respond to good soil fertility like other grain crops; with N, P and K being the most desired nutrient. Therefore, the low level of these elements in the savannah soil could have been the reason for the low growth observed in the Amaranthus species on the control plots in this study. Amaranthus species on the control plots had the lowest values in the growth and grain yield parameters measured. This was in line with our expectation of better growth with nitrogen fertilizer application. The inadequacy of the nutrient in the native soil could further be proved by the good response of all the Amaranthus species to the first dose of NPK fertilizer even at 125 kg ha-1 compared with the control treatment. Higher growth values exhibited by the Amaranthus species under 2501 kg ha-1 NPK treatment compared with 125 kg ha-1 at 4 and 5 WAP showed that application of the fertilizer at 125 kg ha-1 was inadequate for their growth.

Application of the NPK fertilizer at 250 kg ha-1 seems to provide adequate nutrient for the Amaranthus species up to 5 WAP, by showing slightly higher growth values than that of 125 kg ha-1 after the first dose of the fertilizer at this rate. Also at 4 WAP, Amaranthus species generally showed comparable values in root and shoot growth under 2501, 2502 and 500 kg ha-1 NPK fertilizer treatments. This contradicts our expectation of a linear response with increase in fertilizer rate. Similar report from Myers (1998) also showed that yield, as well as other nitrogen-responsive characteristics in Amaranthus generally leveled off at 90 kg ha-1 and was not changed further by a doubling of fertilizer rate to 180 kg ha-1. This possibly indicates that, application of a single dose of the fertilizer at 500 kg ha-1 at planting may be in excess of need even though this rate produced the highest values in the growth parameters at 4 and 5 WAP in Amaranthus species. On the other hand, the single dose application of 500 kg ha-1 NPK in comparison with 125 and 2502 kg ha-1 with second dose produced lower values in growth and yield parameters in Amaranthus species during the experiment. Therefore, the species response to the fertilizer rates was not linear. Apart from the possibility of 500 kg ha-1 NPK rate being too high for the plant at the initial stage of growth, a lot of it might have been washed away in run-off during rainfall or even leached from the reach of the plant root. This report was similar to that of Scholberg et al. (2000) who indicated that, tomato plant only makes use of about 10% of the nitrogen applied pre-plant during the initial growth period and that it may be necessary to reduce the amount of pre-plant fertilizer to as little as 20% of the current production amounts.

The second dose application of the fertilizer at 125 and 2502 kg ha-1 boosted plant growth and development. This was shown by the fact that, 125 kg ha-1 NPK treatment after the second dose application produced higher values in growth parameters than 2501 kg ha-1 at 6 and 7 WAP. Also, 2502 kg ha-1 NPK treatment produced higher growth in Amaranthus species at 6 and 7 WAP than all the other treatments. This could be attributed to the fact that, the plant at this growth stage of second dose application (5 WAP) was undergoing rapid growth and made maximum use of the applied nutrient and thereby possibly limited the proportion lost. According to Henson and Bliss (1991) nitrogen applied during the vegetative stage (about 4 weeks after emergence) of Phaseolus vulgaris (L.) produced higher seed yield than N applied at planting, flowering, or during pod-fill.

The response of the root of Amaranthus species to fertilizer application (especially the second dose) was not dramatic as such. For instance, the 2502 and 500 kg ha-1 NPK treatments produced comparable root growth at 4 and 5 WAP and that even at 6 WAP, the root growth values was still slightly higher at 500 kg ha-1 than 2502 kg ha-1 NPK treatment. This response differed from the shoot responses to the applied fertilizer. This possibly showed that, N had less influence on root growth or supported shoot growth better than root growth or required longer time lapse than shoot before its effects are manifested on root growth. According to Liebman and Davis (2000) root and shoot responses to nutrient enrichment often differ among plant species.

The higher growth and grain yield in Amaranthus species in site II than I was probably due to higher native soil fertility at the site II than site I, before the application of fertilizer in each site. This could be seen in the physico-chemical properties of the soil in Table 1. Myers (1998) stated that, studies with grain Amaranthus in tropical regions have shown inconsistent yield responses to N fertilizer, reflecting the diversity of environments and conditions under which the studies have been conducted.

The Amaranthus species response to the fertilizer rates was generally similar as expected. Therefore, the higher plant height, shoot growth, dry weight/10 plants and per hectare and total seed weight/10 plants (data not included), although with the lowest leaf number though bigger leaf area in A. hybridus than the other species was just the manifestation of its genotypic trait. This species usually considered as improved species normally appear more luxuriant than the other species. This observation was however contrary to that of Elbehri et al. (1993). They reported that, Amaranthus lines responded differently to applied N fertilizers and that A. cruentus lines maximized yields at lower levels of applied nitrogen.

On the other hand A. hybridus var. cruentus showed the highest values in root fresh weight, shoot water content, 1000-grain weight and total grain weight/ha. The observation on A. spinosus contrasted with these showed that Amaranthus hybridus var. cruentus seems to be genetically prone to produce bigger and heavier grains compared with the other species. In conclusion, this study showed that, application of this compound fertilizer (NPK: 27: 13: 13) at the various rates generally stimulated the growth of these Amaranthus species, being at best at 2502 kg ha-1 NPK treatment. However, it will be good to evaluate the species response to rates lower than 2502 kg ha-1 NPK treatment The response of A. hybridus var. cruentus to the applied fertilizer showed that, the growth of this species in the southern part of the country (though considered more fertile than the north), as well as in the north, could be increased with the application of this NPK fertilizer thereby leading to better economic returns especially when applied in two split doses.

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