ABSTRACT
The field experiment was
conducted during the 2011 dry season at the Irrigation Research Fields of the
Institute for Agricultural Research (IAR), Samaru, Nigeria, to evaluate yield
and soil water balance of two cowpea varieties under deficit irrigation and
mulch using locally assembled weighing- type micro lysimeter. The treatments
comprised of three levels of irrigation water application depths (50%, 75% and
100% of weekly reference evapotranspiration (WRETo)) and two levels of mulch
(No mulch-NM, and black polyethylene mulch -BPM) and two varieties of cowpea
(SAMPEA7 and 9) laid
in a group balanced block on split-plot design. The result showed that the
yield of the cowpea pods ranged from 0.29 t/ha to 1.29 t/ha. The highest yield
was obtained from SAMPEA7 treatment irrigated at 100% WRETo with BPM. The
drainage depth ranged from 3.9 mm to 89.5 mm with the least value obtained by
SAMPEA9 at 50% WRETo and NM. The highest depth was by SAMPEA9 at 100% WRETo and
BPM. In comparison, SAMPEA7 gave less drainage water compared to SAMPEA9. The
study showed that crop water use of cowpea ranged from 187.6 mm to 335.6 mm for
SAMPEA9 and 191.3 mm to 315.8 mm for SAMPEA7 with the least values occurring at
50% WRETo and NM. The estimated values of Kc for the two cowpea varieties at
initial, crop development, mid and late season stage were 0.32, 0.58, 0.63 and
0.39, respectively for SAMPEA7 and 0.32, 0.63, 0.72 and 0.34, respectively, for
SAMPEA9 varieties. The highest crop water use efficiency (CWUE) and irrigation
water use efficiency (IWUE) were 3.76 kg/ha-mm and 2.11 kg/ha-mm, respectively,
for SAMPEA7 variety and 2.94 kg/ha-mm and 1.68 kg/ha-mm, respectively, for
SAMPEA9 variety. The crop yield response factor (Ky) was found to be 1.10 for
the BPM treatments and 1.22 for the NM treatments. In conclusion, SAMPEA7
variety irrigated at 75% WRETo with BPM gave the highest
WUE of 2.11 kg/ha-mm which translates to highest yield per unit depth of
water-use.
CHAPTER ONE
INTRODUCTION
1.1 Background
Cowpea is one of the most
widely adapted, versatile and nutritious of all the cultivated grain legumes
(Dugje et al., 2009). With the increasing need of this crop, it is
necessary to accelerate and expand its production all year round. This could
mean making an effort to grow the crop under irrigation so as to have more than
one cropping season in a year which would increase its production.
Nigeria has two distinct
seasons – the rainy season, lasting from mid of March to the end of October,
and the dry season, lasting from November to March. In the dry season, there is
virtually no rain and irrigation remains the only option for crop production.
There is stiff competition for water by the agricultural, domestic and
industrial users during the dry season, hence there is the need for farmers to
conserve and make judicious use of the available water (Adekalu and Okunade,
2006).
Studies are needed to increase
the efficient use of the available water. Regulated deficit irrigation with
mulching is one among many practices that is fast gaining ground, and it
appears a very promising option at achieving the goal of more crops per unit
volume of water, if properly adopted. The development of new irrigation
scheduling techniques such as deficit irrigation and identifying the sensitive
crop growth stage to water stress is one way to enhance crop productivity with
less water (Bekele and Tilahun, 2007). Regulated deficit irrigation scheduling
practice is a technique of withholding or skipping irrigation, or reducing the
amount of water applied per irrigation at some stages of the growth with the
aim of saving water, labor, and energy without adverse effect on yield
performance. This practice
leads to some degree of moisture stress on the crop and likely reduction in
crop yield (Smith et al., 2002: Prichard et al., 2004; Zhang et
al., 2004).
The objective of regulated
deficit irrigation is to save water by subjecting crops to periods of moisture
stress with minimal effects on the yields. The water stress results in less
evapotranspiration by closure of the stomata, reduced assimilation of carbon,
and decreased biomass production. The reduced biomass production has little
effect on ultimate yields where the crop is able to compensate in terms of
reproductive capacity (Stone et al., 2001).
Mulching involves the use of
materials to cover the cropped soil surface with the aim of reducing
evaporation, conserving soil moisture, modifying soil temperature, structure
and improving aeration. It also suppresses weeds and reduces erosion.
(Hassan,1996 Plauborg et al., 1996). A better understanding of crop
yield-water application interaction and the effects of irrigation levels and
mulch (covering the soil surface) on the relationship between transpiration,
evaporation and evapotranspiration for various crop is necessary to improve the
management of irrigation water resources (Kadayifci et al., 2004).
Furthermore, evaporation and
transpiration occur simultaneously and there is no easy way of distinguishing
between the two processes directly on the field. The amount of water required
to compensate the evapotranspiration loss from the cropped field is defined as
the crop water requirement. Although the values for evapotranspiration and crop
water requirements are identical, crop water requirement refers to the amount
of water that needs to be supplied, while evapotranspiration refers to the
amount of water that is lost (Richard et al., 1998). The water balance
method provides a simple but robust
means of continuous measurement
of evapotranspiration (ET) from different species of vegetation (Granier et
al., 1990; Gholipoor, 2007).
The Institute for Agricultural
Research (IAR), Samaru has released several varieties of cowpeas in the last 15
years. Although some of these varieties are planted under irrigation, the
irrigation water requirements and their crop coefficient (Kc) values have not
been systematically evaluated. A systematic evaluation of these parameters
involves an isolation of the crop growing medium, which is the soil, so that
water input and output into and out of the system will be effectively
monitored. By so doing, the soil water balance components will be appropriately
determined. One device that can be used for such study is the soil lysimeter.
1.2 Statement
of the Problem
Despite the potentials and
importance of cowpea, there is little, if any documented research information
on cowpea production under irrigation in Nigeria. Production practices of a
crop under irrigation must necessarily be stated independently from the
rain-fed crop because the two seasons are not comparable. Most of the agronomic
research to date on cowpea has been focused on the rain-fed crop by the
Institute for Agricultural Research (IAR), Samaru Zaria (Mohammad, 2011).
It is an established fact that
one of the important factors limiting the development of agriculture in the
semi-arid region is water. Samaru which is located within this region is one of
agricultural areas in Zaria, Kaduna State. However, there are large potentially
irrigatable lands which are not irrigated due to insufficient or lack of
irrigation water, which led to the necessity of optimizing and managing the use
of water for agricultural production (Oiganji, 2010). There is also uncertainty
as to the availability of water in adequate amounts and times, especially where
storage facilities such as dams are absent.
This necessitates development
of water management strategy to avert water stress in crops; which if proven
advantageous, could assist farmers as most of them are at subsistence level and
they are economically weak with low ability to withstand risks.
With the recent screening and
release of improved cowpea varieties that are high yield photo-insensitive and
early maturing, nine varieties of cowpea for different ecologies have been
developed and released for production by IAR. The most popular are SAMPEA6 and
SAMPEA7 which are resistant to many stress factors, and SAMPEA9 which is dual
purpose (high grain and fodder yields) (Agricultural Research Council of
Nigeria, 2017). The study therefore applied the use of a weighing-type soil
micro-lysimeter to study the yield and water balance of two varieties of cowpea
(SAMPEA7 and SAMPEA9), under mulch and deficit irrigation.
1.3 Justification
of the Study
In Nigeria, the greatest
production of cowpea comes from the northern region. The north produces about
1.7 million tonnes from 4 million hectares. This represents over 60% of total
production (FAO, 2005). During the dry season, water is usually provided from
both irrigation facilities and residual moisture of wetlands (Inaizumi et al.,
1999). But water is a limiting factor in the expansion of irrigated areas and
in the production of food. As the population increases, greater competition for
the water supply makes conservation and efficient use of water imperative (Eric
et al., 1981).
Rising cost of Irrigation
pumping, low commodity prices, inadequate irrigation system capacities and
limited irrigation water supplies are the reasons for which many irrigators
deliberately apply less water than is required for maximum yield. (Craciun and
Craciun, 1999). One means of determining when irrigation should be supplied is
through the use of a soil water balance or soil water budget (Tim, 1996).
Cowpeas are exposed to
varying levels of
environmentally induced stresses during their growth stages, and limited
information exists on reliable estimates of evapotranspiration (ETo) to be used
for forecasts, to achieve high irrigation water use efficiency in semi-arid
environment, particularly under micro-irrigation (MI) system, such as in IAR
Research Farm at Samaru Zaria.
Improved irrigation management
requires adequate information on the nature and degree of responses of various
growth stages to water stress. Hence, with the changes that have taken place in
the global climates in the last one decade, and with new varieties of crops
released, there is the need to re-validate the existing body of information on
crop water requirements, crop coefficients and the water stress coefficients.
The reason for this is because these parameters depend on climatic factors and
crop characteristics. With these background considerations, a comprehensive
field investigation was undertaken to study the water balance components of two
IAR cowpea varieties under Irrigation.
1.4 Aim
and Objectives of the Study
The
aim of this study was to evaluate the yield and water balance of two IAR cowpea
varieties (SAMPEA7 and SAMPEA9) under mulch and deficit irrigation using
weighing-
type micro-lysimeters.
The
objectives are;
a)
To determine grain yield and crop
water use of the cowpea varieties under different water application regimes and
mulch practice.
b)
To develop crop coefficient curve
for the cowpea varieties under limited and unlimited water supply conditions.
c)
To express the yields and water use
relationship for the cowpea varieties.
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Item Type: Project Material | Size: 84 pages | Chapters: 1-5
Format: MS Word | Delivery: Within 30Mins.
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