Effect of Cow dung Manure on the Productivity and Nitrate Content of Spinach (Spinacia
oleracea) at Samaru, Zaria, Nigeria
2
Ibrahim, U. 3*Ahmadu I.S. 2Yahqub M. 1Goma L.
*Corresponding Author: ahmaduidrissalihu@gmail.com
08169092836
1Department of Agronomy, Faculty of Agriculture Ahmadu Bello University, Zaria.
2Samaru College of Agriculture, Division of Agricultural Colleges, Ahmadu Bello University, Zaria
3College of Agriculture and Animal Science, Mando, Division of Agricultural Colleges, Ahmadu Bello University, Zaria.
ABSTRACT
The amount of nitrate found in vegetables depends on its genotype, and a variety of other
conditions such as soil, fertilizer, growth, and storage conditions. To increase the nitrate content
of vegetables there is the need to study the effect of organic fertilizer application at different
rates. The objective of this research was to investigate the effect of cow dung manure at different
rates on growth, yield and nitrate content of spinach oleracea. The experiment was conducted at
two different locations at the Teaching and Research Farm of Samaru College of Agriculture,
Ahmadu Bello University, Zaria (Latitude 11° 11' N, Longitude 07° 38' E, and 686 meters above
sea level) which is in the northern Guinea Savanna ecological zone of Nigeria during the 2019
wet season. The treatments consist of five levels of cow dung manure (0.t/ha, 1.0t/ha, 1.5t/ha,
2.0t/ha,2.5t/ha, 3.0t/ha of cow dung manure, the recommended NPK (100kg/ha) for spinach in
the study area and the check, which is non application of any type of fertilizer. This was
factorially combined and arranged in a Randomized Complete Block Design (RCBD) and
replicated three (3) times. There were 7 treatments in each replication and 21 treatments in the
trial. All cultural practices were carried out as at when due. Data collected on growth parameters
include plant height, number of leaves plant-1, stem diameters and leaf area plant-1, whereas data
collected on yield parameters included fresh weight yield plot-1, dry weight yield plot-1, fresh
weight yield hectare-1. All data collected were analysed using Statistical Analysis System (SAS)
and the mean were separated using Duncan Multiple Range Test (DMRT). The effect of organic
fertilizer was not significant on both growth and yield parameters at various sampling periods.
This may be because the soil fertility status of the study area was low. There was significant
difference on nitrate content of spinach. The result indicates that the higher the cow dung manure
the higher the nitrate content. Application of 3.0t/ha of cow dung manure gave the highest nitrate
content, while the application of 1.0t/ha gave the lowest nitrate content which was higher than
the control.
Key words: Spinach oleracea, Cow Dung, Nitrate and Zaria
INTRODUCTION
Spinach is an important vegetable crop consumed for its nutritional, medicinal and health
benefits. It also serves as source of income for small holder farmers, particularly the rural women
1
who produce and sell the crop. Nitrogen fertilizers have been identified as one of the major
factors that influence optimum crop yield in vegetables. It has been reported that Green leafy
vegetables such as spinach, generally contain higher levels of nitrate than other foods. Therefore,
excessive application of N may result in higher nitrate concentration in spinach.
Nitric oxide (NO) is oxidized in the body naturally to form nitrite (NO2-) and nitrate (NO3-)
(Bryan and Ivy, 2015). The nitrate taken in through diet is typically found in functional foods
such as dark leafy vegetables for like lettuce, broccoli, cabbage, spinach, amaranths and fruits
like strawberries. About 85% of dietary nitrate comes from vegetables, while the remaining
amount can be obtained from drinking water. Vegetables in diets are functional foods that aid in
lowering blood pressure due to the dietary nitrates found in them, which have a beneficial effect
on the circulatory system by decreasing blood pressure (Lidder and Webb, 2013). Nitrate can
function as an antioxidant when it is converted to nitric oxide (Maeda, 2009). This quality allows
for the possibility to be beneficial and be able to prevent diseases and promote efficiency in the
regional blood flow in patients with sickle cell (Milkowski et al., 2010). Conversely, it has also
been established that excessive intake of nitrate due to increasing consumption of vegetable,
especially leafy crops may increase the risks of nitrate and nitrosamine exposure.
Nitrogen is an essential element for plant growth and development; however, due to
environmental pollution, high nitrate concentrations accumulate in the edible parts of these leafy
vegetables, particularly if excessive nitrogen fertilizer has been applied. Consuming these crops
can harm human health, thus developing a suitable strategy for the agricultural application of
nitrogen fertilizer is important. Therefore, it is important to increase crop yield using N without
leading to excessive accumulation of nitrate beyond the 2500 ppm maximum limit for nitrate in
fresh vegetables. The amount of nitrate found in vegetables depends on its genotype, and a
2
variety of other conditions such as soil and season, fertilizer, the type of cooking procedure, and
crop types (Hord et al.,2009; Lundberg et al., 2006).
The study was carried out to determine the effect of different rates of cow dung manure
application on the growth, yield and nitrate content of spinach with a view to increase its
productivity, thereby improving the health and nutritional benefit of smallholder farmers in
northern Nigeria.
MATERIALS AND METHODS
The experiment was conducted at the Teaching and Research Farm of Samaru College of
Agriculture, Ahmadu Bello University, Zaria (Latitude 11° 11' N, Longitude 07° 38' E, and 686
meters above sea level) which is in the northern Guinea Savanna ecological zone of Nigeria
during the 2019 cropping season. The treatments consist of five levels of cow dung manure (0 t
ha-1, 1.0 t ha-1, 1.5 t ha-1, 2.0 t ha-1, 2.5 t ha-1, 3.0 t ha-1) the recommended NPK rates (100 kg ha1
) for spinach in the study area and the check, which is non application of any type of fertilizer.
This was factorially combined and arranged in a Randomized Complete Block Design (RCBD)
and replicated three (3) times. There were 7 treatments in each replication and 21 treatments in
the trial. The trials were conducted in two locations during the wet season.
Soil samples were taken randomly at 0-30 cm soil depths from the experimental sites before
establishing the trial. A tubular auger was used to take the samples. The composite sample was
analysed in the laboratory to determine their physical and chemical properties such as pH was
measured in water (1:2.5 soil: water) and in 0.01M CaCl2 using a cyber-scan 20 pH meter, soil
organic carbon was determined through the wet oxidation method (Walkely and Black, 1965).
3
The total nitrogen was determined by micro kjeldahl digestion distillation method (Bremmer,
1965). While available phosphorous was determined by Bray 1 method (Bray and Kurtz, 1945).
The exchangeable cations (Ca, Mg, K and Na) and the cation exchange capacity (CEC) were
determined using standard procedures as described by (Agbenin, 1995). Particle size was
determination hydrometer method as described by Agbenin, (1995) Samples of the cow dung
were also analyzed for chemical properties. NO2- content of the vegetable at harvest was
analyzed using standard procedure to determine the effect of the different treatments on the
vegetable. Weeds were controlled by hand pulling as at when necessary.
The land was ploughed, harrowed before planting, and marked into plots of 3 x 2 m (6 m2) from
which sunken beds was made manually to accommodate for the manure. The blocks were
separated by an alley of 1 m and the plots were demarcated with high bunds of 20 cm to
minimize lateral movement of fertilizer from one plot to another, in addition to the conservation
of water within the plot. The cow dung manure was applied as treatment-1 at 2 weeks before
planting which was uniformly spread on the beds and lightly worked into soils with hoe. The
land was harrowed into a fine tilt and beds of 3 x 2 m2 (6 m2) were made where the seeds were
sown by broadcasting and lightly covered with soils. The seeds were planted at a spacing of 20 x
20 cm. The beds were mulched with straw grasses. The mulch was removed after seed
emergence to facilitate seedlings establishment.
Plant height was measured from ground level of the tip of growing point using a meter rule and
the average height of the tagged plants was determined. Plant stem diameter of the tagged plants
was measured using Vernier caliper, the average was calculated and recorded. Number of leaves
per plant was determined by counting the total number of leaves on each tagged plant and the
4
average was taken. Leaf area was determined using a Ll-3100c leaf area meter and the average
was determined. Fresh vegetables were harvested at 6 WAS and weighted. The weight
determined was later expressed in tons ha-1. The samples were weighted using Metter weighing
balance. Fresh weight per plant was obtained by up-rooting two plants per plot at 6 WAS, the
roots were washed to remove the soil, samples were later put into a small, marked envelope
labeled with the plot number and oven dried at temperature of 70° to a constant weighed. Harvest
was done at physiological maturity, 6 WAS, all plants in the net plot was harvested to determine
yield and nitrate content while plants outside the net plot will be used for analysis.
Data collected was subjected to Analysis of Variance (ANOVA) using general linear model
GLM of the Statistical Analysis System package and the means were separated using Duncan’s
Multiple Range Test. All statistical procedures were done as described by (Gomez and Gomez,
1984).
RESULTS AND DISCUSSION
The physical and chemical properties of the soil of the experimental site during the 2019 wet
season in both locations are shown in Table 1. The soil type of the experimental sites were sandy
loam and soil's texture distribution ranges from 12-16% clay, 28-34% silt and 54-56% sand. The
soils in location I ranges from very strongly acidic to strongly acidic and location II vary from
slightly acidic to neutral. Organic carbon, total nitrogen and available phosphorus in all locations
were low as described by (FMARD 2002). The calcium, potassium and sodium content are high
and exchangeable magnesium was medium in all the locations.
There were no major differences in the chemical composition of cow dung manure used for the
study is shown in Table 2, revealed that nitrogen, phosphorus, and potassium were very low.
5
Similarly, Tables 3 and 4, shows the response of some growth and yield characters of spinach in
relation to application of organic fertilizers at the two locations. The result revealed that there
was no significant difference in plant height, stem diameter, number of leaves and leaf area of
spinach in relation to application of organic fertilizer as shown in Tables 3 and 4 in both
locations.
Similarly, the effect of organic fertilizer on dry weight, fresh weight per plant and yield of fresh
ha-1 of spinach shows that there was no significant difference in all the yield parameters at
harvest as shown in Tables 3 and 4. As observed from the result, there was significant difference
on nitrate content which increased with increasing application of cow dung manure.
The non-significant differences in both growth and yield parameters at 6 weeks after sowing may
be due to the low fertility status of the soil of the study area (Table 1) combined with the low
NPK values in the cow dung manure (Table 2). The low availably of these nutrients in the soil
coupled with cow dung manure couldn’t supply enough nutrient to meet the fertility requirement
of the crop. This also proved that manure application rates should be based on crop nutrient
requirements or removal. There was significant difference in the nitrate content of spinach with
3.0 t ha-1 tons of cow dung manure having a higher nitrate content in first location and NPK 100
kg ha-1 in the second locations. Similarly, 0 t ha-1 ton of cow dung application led to low nitrate
content in vegetables. manure application has been associated with increased nitrate (NO3)
availability from soils Rayan and Aula (2020), and excess nitrate will be accumulated in the
vacuoles of plants tissue instead of being converted to amino nitrogen. Higher nitrate in
vegetables treated with NPK 100 kg ha-1 in the second location could be attributed to the
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increase in Nitrate levels with the use of synthetic fertilizers compared with animal manures. The
nitrate accumulation in vegetables of all the treatment (Tables 3 and 4) were less than 2500
mgkg-1 which is maximum limit for nitrate in fresh vegetables given by WHO/FAO (1988). The
nitrate levels were found in vegetable amaranths do not pose a serious health problem to healthy
individuals.
CONCLUSION
Based on the result of this experiment, it can be concluded that the effect of cow dung manure
was not significant on both growth and yield of Spinach (Spinacia oleracea) at Samaru, Zaria.
However, there was significant difference on nitrate content of spinach. The result indicates that
the higher the cow dung manure the higher the nitrate content. Application of 3.0t/ha of cow
dung manure gave the highest nitrate content, while the application of 1.0t/ha gave the lowest
nitrate content which was higher than the control. Although all the treatments had nitrate content
below the maximum limit of the 2500 ppm for nitrate in fresh vegetables.
7
REFERENCES
Agbenin, J.O. (1995). Laboratory Manual for Soil Plant Analysis. Dept. of Soil Science, Ahmadu
Bello University, Zaria.
Bray, R.H. and Kurtz, L.T (1945). Determination of Total Organic and Available Phosphorous.
Soil Science, 59: 37-56.
Bremmer, J.M. (1965). Total Nitrogen. In: Methods of Soil Analysis, (Ed. Black C.A). Amer.
Society of Agronomy, Madison, Wisconsin, USA. 9(2): 1149-1178.
Bryan, N., and Ivy, J., (2015). Inorganic Nitrite and Nitrate: Evidence to Support Consideration
as Dietary Nutrients. Nutrition Research, 35: 643-654.
FMARD (2002): “Agriculture in Nigeria: Policy (Before and Now) Analysis of the Existing
(1988) Agricultural Policy and the Revised Policy” Federal Ministry of Agriculture and
Rural development, Abuja
Gomez, K. A., & Gomez, A. A. (1984). Statistical procedures for agricultural research. John
wiley & sons.
Hord, N., Tang, Y., and Bryan, N., (2009). Food Sources of Nitrates and Nitrites: The
Physiologic Context for Potential Health Benefits. The American Journal of Clinical
Nutrition, 90: 1-10.
Lidder, S., and Webb, A. J. (2013). Vascular Effects of Dietary Nitrate as Found in Green Leafy
Vegetables and Beet Root via the Nitrate - Nitrite - Nitric Oxide Pathway. British Journal
of Clinical Pharmacology, 75(3): 677- 696.
Lundberg, J., Feelisch, M., Björe, H., Jansson, E., and Weitzberg, E., (2006). Cardio-Protective
Effects of Vegetables: Is Nitrate the Answer? Nitric Oxide, 15: 359-362.
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Maeda, H., (2009). Controlling Oxidative Stress: Therapeutic and Delivery Strategies. Advanced
Drug Delivery Reviews, 61(4): 285-286.
Milkowski, A., Garg, H., Coughlin, J., and Bryan, N., (2010). Nutritional Epidemiology in the
Context of Nitric Oxide Biology: A Risk-Benefit Evaluation for Dietary Nitrite and
Nitrate. Nitric Oxide, 22: 110-119.
Rayne, N., & Aula, L. (2020). Livestock manure and the impacts on soil health: A review. Soil
Systems, 4(4), 64.
Walkey, R. and Black, C.A. (1965). Chemical and Microbial Properties. In: Black, C.A., (Ed.).
Methods of Soil Analysis Part 2. American Society of Agronomy. 12: 1575.
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Table 1: Physical and Chemical Properties of the Soil of the Experimental Sites
Soil Parameters
Units
Location I
Location II
Particle size distribution
Clay
g kg-1
16.00
12.00
Silt
g kg-1
28.00
34.00
-1
Sand
g kg
56.00
54.00
Textural class
sandy loam
sandy loam
Chemical properties
pH in water 1: 2.5
5.28
6.83
pH in Cacl2 1: 2.5
4.78
5.99
Soil Salinity
dsm-1
0.01
0.05
-1
Organic Carbon
g kg
1.34
0.58
Total Nitrogen
g kg-1
0.21
0.35
Available Phosphorus
mg kg-1
9.81
13.95
Exchangeable Cation
K
cmol kg-1
1.71
0.73
-1
Mg
cmol kg
0.92
0.92
Ca
cmol kg-1
8.85
7.70
-1
Na
cmol kg
0.87
0.77
Exchangeable acidity
cmol kg-1
1.20
0.80
-1
ECEC
cmol kg
13.55
10.92
Table 2: Analysis of the Cow Dung Manure Used in Both Locations
Total nitrogen (g kg-1)
13.11
13. 0
Available Phosphorous (mg kg-1)
3.96
4.00
Potassium (cmol kg-1)
1.17
1.20
10
Table 3: Effect of Cow dung Manure on Growth, Yield and Nitrate Content of Spinach During the 2019 wet season at 6 Weeks After Planting
in the first location.
Treatments
Plant height Plant diameter Number of leaves
Leaf area Fresh weight Dry weight Yield Nitrate content
cm
cm2
kg plant-1
kg ha-1
mg kg-1
-1
0 t ha
8.92
0.22
9.83
15.33
2.20
1.20
16,000
845c
1.0 t ha-1
8.33
0.28
11.67
15.90
3.47
1.63
23,111
1,044b
1.5 t ha-1
10.80
0.28
11.50
15.93
2.97
1.50
19,778
1,044b
-1
2.0 t ha
11.95
0.33
11.33
21.53
6.03
2.70
40,222
1,154b
2.5 t ha-1
10.67
0.30
11.67
9.57
3.23
0.80
21556
1,206b
-1
3.0 t ha
12.95
0.35
12.17
15.03
4.63
1.77
30889
1,799a
NPK 100 kg ha-1
10.18
0.20
9.17
12.17
3.10
0.80
20,667
1,206b
SE+
0.698
0.103
0.504
1.049
0.607
0.411
49.611
0.332
Table 4: Effect of Cow dung manure on Growth, Yield and Nitrate Content of Spinach During the 2019 Rainy Season at 6 Weeks After Planting for
the second location.
Treatments
Plant height
Plant diameter
Number of leaves Leaf area Fresh weight Dry weight
Yield
Nitrate content
2
-1
-1
Units
cm
cm
kg plant
kg ha
mg kg-1
0 t ha-1
7.32
0.22
8.17
15.03
1.20
0.47
17564.80
9.27c
-1
1.0 t ha
6.57
0.23
9.50
15.43
1.63
0.67
25371.26
11.46b
1.5 t ha-1
9.05
0.25
9.83
15.33
1.50
0.70
21712.29
11.46b
-1
2.0 t ha
9.78
0.23
8.67
19.70
2.70
1.23
44155.71
12.67b
2.5 t ha-1
9.23
0.25
9.50
9.70
0.80
0.50
23664.18
13.29b
3.0 t ha-1
11.00
0.30
10.17
14.33
1.77
1.00
33909.94
19.75b
-1
NPK 100 kg ha
8.58
0.17
7.83
10.57
0.80
0.53
22688.23
13.97a
SE+
0.668
0.088
0.507
1.003
0.411
0.306
55.106
0.364
11