Different Irrigation Methods for Okra Crop Production under Semi-arid Conditions

Different Irrigation Methods for Okra Crop Production under Semi-arid Conditions

Abubaker B. M. A1*, Mohammad Alhadi2, Yu Shuang-En1 and Shao Guang-Cheng1

1Key Laboratory of Efficient Irrigation-Drainage and Agricultural Soil-Water Environment in Southern China, College of Water Conservancy and Hydropower, Hohai University, Nanjing 210098, China; 2Department of Climate Change, UNESCO water institute, Inndyr 8140, Norway

Abstract – Irrigation methods have significant impact on okra production. Okra is popular vegetable crop used in Sudan. A field study was conducted to compare the efficiency and performance of the Drip irrigation (DI) and the conventional Surface irrigation (SI) systems under the same conditions for producing okra. An open field DI was installed with laterals 40m apart and 1m spacing. Emitters were inserted at 40cm spacing. A nested experimental design was used with two replications. Three okra varieties were tested for their watering requirements and agronomic performance. The parameters measured included plant height, stem diameter, root length, root weight and yield production. The study included some soil properties, infiltration rate, crop water requirement, crop water use efficiency, and uniformity of water distribution for both systems. The okra agronomic parameters except root length and weight were significantly (p 0.05) affected by DI and SI. There were no significant differences between okra varieties. Results showed that the uniformity of water distribution of the DI was relatively 81.4

% high. The water applied to crop was greater than the actual crop water requirement and the efficiency of the DI was 126.5

% over that of the SI. Maximum yield of 249.71kg ha-1 was obtained by using DI. Sandy clay loam soil with a relatively high infiltration rate of 1.8 cm h-1 that suits the DI system is recommended.

Keywords Okra, drip irrigation, surface irrigation.

1. INTRODUCTION Surface irrigation (SI) method is the widely applied

   in Sudan, due to cost-effectiveness and low maintenance

   requirements but, the irrigation efficiency is low due to losses by runoff in the heavy soils and deep percolation in light soils. Low efficiency leads to increment in the cost of irrigation, labour and water shortage compared with the modern irrigation systems such as sprinkler and drip irrigation (DI) which has high efficiency and minimum water losses. DI is one of the recent irrigation methods used in improving crop production and it is becoming increasingly popular in areas with problems of water scarcity and salinity. Drip irrigation has considerable advantages over furrow or even sprinkler irrigation in terms of water application efficiency is capable to small and frequent applications of water has created interest among the farmers because of less water requirement, increased production and better quality production [1]. Water application scheduling is a critical issue for DI system efficiency evaluation, because excessive or inadequate

   irrigation reduces yield. The optimal use of irrigation can be characterized by the supply of sufficient water according to plant needs in the deeper soil layers [2]. The obstacle for the spread and adoption of the DI is capital cost, although growers may be able to recover their cost in few years under favourable yields and market conditions [3]. The DI method has not yet been employed for extensive large scale crop production in Sudan. Survey analysis revealed that DI system is adopted in some areas in Sudan for producing crops in green houses, small private farms and gardens [4]. Okra, a widely distributed crop is one of the oldest cultivated crops in many parts of the world with its origin from Ethiopia and Sudan [5],[6]. It is an important vegetable because it is rich in vitamins, folic acid, carbohydrates, phosphorus, magnesium, calcium, potassium and other minerals [7]. Okra production is estimated at 6 million tons per year in the world [8]. In Sudan it is estimated at 256,000 tons [9]. The total area and production of okra in Sudan is reported to be 21.500 ha and

   11.90 t ha-1 respectively with 3.24 % share in world production. In Sudan, a number of local mixed cultivation, with Indian and American introductions, are grown in the irrigated areas. To meet the increasing demand on okra crop to satisfy the needs of the growing population in Sudan, Elsilait Agricultural Project (EAP) Khartoum initiated rapid expansion of irrigation throughout the cities. Determination of the required amount of water for okra crop irrigating is important for maximum plant production, better water saving and management practices, and it can be obtained from either DI or SI methods. Accordingly, this study is aimed to compare the DI and the conventional SI method for okra crop production in terms of distribution uniformity, water usage efficiency (WUE), yield and yield components, reference crop evapotranspiration and crop water requirement was conducted.

2. MATERIALS AND METHODS

   2.1 Study area and field conditions

   Field experiment was conducted at EAP scheme site, Khartoum north of Sudan (15o40N and 32o32E, with an elevation 382m above mean sea level). The climate is tropical semi-arid which is hot dry in summer and mild dry

   2.3 Estimation of irrigation requirement and discharge measurement

   Metrological data were collected from Sudan metrological authority as will be discussed later in details. Crop water requirement was calculated using the following formula [11]:

   in winter with a great seasonal variation in temperature. Tests for soil texture of the experimental site are dominated by sandy clay loam comprising of 54.8% sand, 13.7% silt

   ETC

   ET KC ,

   and 33% clay with pH of 7.8. Average values for field capacity, bulk density and permanent wilting point are 36%, 1.3 gm/cm3 and 26% respectively. The experimental soil was prepared by disc plough followed by leveler and ridging for both irrigation systems. The study area is 8400 m2 with natural slope and uniform of soil texture. A factorial complete block design was used for the two

   irrigation methods, (Fig. 1). Three okra (Abelmoschus

   where: ETc: Crop water requirement (mm/day); ET: Reference crop evapotranspiration (mm/day); Kc: Crop coefficient.

   Reference crop evapotranspiation (ET) was calculated according to Penman-Montieth, as suggested by [11]:

   900

   esculentus) cultivars were selected for the study namely

   Khartoumia spiny (V1), Pusa Sawani (V2) and karary

   ETo

   0.408Rn G

   U 2ea ed

   T 273

   (V3).

   Fig. 1: Schematic of field experimental

   2.2 System installation and experimental treatments

   The DI system employed includes discharge valve, flushing valve, pressure regulator, screen filter, two sand filter and fertilizer injection with capacity of 100 litters. Two centrifugal water pump with 10, 5.5 hp capacity, driven by an electric motor was used to draw irrigation water from the storage tank at elevation of 12m in the supplying system. This set-up gave a pressure of 3 bars in the main line. The main pipeline is connected to sub-main pipelines of 240, 40m long and 63mm, 38mm in diameter respectively, and made of Polyvinyl Chloride (PVC). It was buried at a depth of 40cm. The lateral pipes are made of black Linear Low Density Polyethylene (LLDPE). The eighteen laterals is each 40m long and 16mm inside diameter. The laterals were joined to the sub-main at 1m spacing. The discharge from each emitters is between 2-4 l/h as recommended by [10]. Emitters were fixed in each lateralat 40cm spacing that coincides with the plant spacing. Related to the SI method, the irrigation system is consisted of 2 ridges, 1m apart and 40m long. The spacing between plants on the ridges is 40cm.

   1 0.34U2

   where: ET: Reference crop evapotranspiration (mm/day); Rn: Net radiation at crop surface (MJ/m2/day); G: Soil heat flux (MJ/m2/day); T: Average temperature at 2 m height (oC); (eaed): Vapor pressure deficit for measurement at 2 m height; U2: wind speed at 2 m height (m/s); : Slope of vapor pressure Curve (KpaoC); 900: Coefficient for the reference crop (kj/kg/day); 0.34: Wind coefficient for the reference crop (S/m); and Y: Psychometric constant (KPa oC).

   The net crop water requirement (NCWR) was calculated by subtracting the monthly effective rainfall (Ref) from crop water requirement (CWR) as:

   N CWR CWR Ref

   The Ref, (mm) was calculated from the total rainfall (TR) mm, according to the empirical formula suggested by USDA Soil Conservation Service [12] as:

   Pe C Ptot d ,

   where: Pe: Effective rainfall (mm/month); Ptot: Total rainfall in a given month (mm/month) and C, d are respectively, fixed percentage that accounts for losses from rainfall and deep percolation.

   The datasets are also used to determine the amount of irrigation water required to bring the soil moisture content level in the effective root zone to field capacity. Ref. [13] proposed an equation to calculate the depth of water applied by considering the fact that only part of the soil volume has to be wet by DI as:

   d 10(Fc PWP ) D Z P

   where: d: Maximum amount (depth) of water to be applied (mm); Fc: Field capacity (cm/m); PWP: Permanent wilting point (cm/m); D: Root zone depth (m); Z: The moisture depletion percentage allowed or desired (decimal) and P:

   The volume of the wet soil is expressed as a percentage of total volume (in decimal). For the determination of the uniform distribution DI system, the discharge (q) was measured 70 emitters chosen for each system, volumetrically using catch cans, and a stop watch. The equation by [14] was used:

   Eu qn 100

   qave

   The pressure was adjusted at 1bar for all the laterals. The measurements were repeated three times and then the average was taken. A regression analysis was used to analyze the rate of flow reduction along laterals. For the SI method discharge was measured using a right angle triangular weir and Parshall flume devices, based on the method developed by [15]. Three representative experimental sites were selected for measuring water infiltration in cm/hr following the procedure described by [16]. WUE of the crop for each treatment was computed from yield and water requirement data.

   1. Yield data

      Three seeds of okra were planted in each hole. The holes were in rows on the side of the ridge with spacing of 1m between ridges and 40cm between plants. Different amounts of water were applied for each furrow and drip irrigated. The interval between irrigations was 7days for SI and 3days for the DI. After one month of sow data was collected for both methods including plant height (cm), plant diameter (cm), root length (cm) and root weight (g). Nine picks for yield (kg/ha) was estimated considering the mean yield obtained from the replicated plots under the treatments then determination by using a sensitive balance. The total pods yield per hectare was estimated considering the mean yield obtained from the replicated plots under the treatments.

   2. Data analysis

   The data obtained from different experiments were recorded as mean ± standard deviation (SD) and subjected to one-way Analysis of Variance (ANOVA). Differences between means were considered significant at P < 0.05.

3. RESULTS AND DISCUSSION

1. Uniformity of Drip Irrigation

   The results revealed that average discharge rate (qave) in emitters along laterals of the DI was 1.05 L/h. Average rate of discharge of the lowest one fourth of the field data (qn) was found to be 0.85 l/h. Thus, the uniformity of DI was found to be 81.4% and that of the SI was between 50- 60% [17]. On the other hand the low water distribution efficiency in furrow may be attributed to water losses by evaporation, deep percolation and run off. The DI system greatly minimizes the losses of such factors and the results are in conformity to that by [15], [18]. Fig. 2 shows the relation between discharge (l/h) and distance (m) along the laterals of the DI method. Generally, there is a negative

   relation between the amount of water conveyed along the lateral line and the position of the lateral on the sub-main line. The correlation coefficient (r) is high 0.6 to 0.8 for those laterals which were within 0-18m for zones a-c along the sub-main line. However, this negative relation dropped to a moderate value of r = 0.38 for those laterals in zone d and then to a weak value of r = 0.23 for the laterals in the lowest part of the sub-main in zone e. The amount of water discharge to the SI indicated that the (r) was 0.42 (Fig. 3). These results agree with the opinion given by [19] who stated that the soil water distribution can be achieved by selecting the appropriate dripper discharge and spacing.

   Fig. 2: Discharge rate of 70 emitters (l/h) on the different laterals along the sub-main line of DI

   Fig. 3: The water discharge rate (m3/s) measured by flow meter and parshal-flume under SI

   The results showed the water infiltration rate values were presented in (Fig. 4) the average of infiltration rate ranges between 1.1 – 1.8 cm/h. Hence the DI was observed to be suitable to soil properties which has high infiltration rate than the SI. The DI supports good plant growth and keep on replenishing the crop root zone which can be attributed to nature of the soil nature as it swells by the wetting phenomenon there by closing soil pores which greatly reduces and impede infiltration [20].

   Fig. 4: Infiltration rate (cm/h) at three random sites of the

   experimental field

2. Crop water requirement (CWR) and water use efficiency (WUE)

Table 1 shows climatic data and the ET. The monthly mean reference of crop evapotranspiration was found to be

6.53 mm/day.

Ref. [8] stated that the water consumption is about 8 mm/day for full-grown crop. Table 2 shows the calculated okra water requirement for four months, which represents the length of its growing season. It was found that the mean okra ETc was 5.1mm/day, and this result agrees with that of

[21] found that there was a linear relationship between okra production and the amount of water supplied. Table 3 shows the monthly mean data of TRF, and the okra NCWR. Rainfall was not encountered during those months, the okra NCWR coincided with ETc. As it appears in Table 4, the DI generally showed higher crop WUE, as compared to SI. The efficiency of the DI was 126.5 % over that under the SI. This might be due to moisture conservation under DI

which is mostly due to prevention of deep percolation and evaporation from soil surface in the study area.

1. Agronomic parameters

   The plant heights (cm) for the five reading after 30, 45, 60, 75 and 90 days showed that there was a significant difference between DI and SI (Table 5). In contrary, there were no significant differences between varieties of okra and interaction (system × varieties). For all the growth stages of the okra plants were taller under the DI as compared to that of the SI system (Fig. 5). The mean plant height after 90 days under DI and SI system was 49.51 and 33.37cm, respectively (Table 6), which conforms, to the results of [22]. Stem diameter (Table 7) after 30, 45, 60, 75 and 90 days from plant growing, showed no significant differences between DI, SI and between okra varieties well as the interaction (i.e. system× varieties) in the first and second reading of plant diameter. Whereas, significant differences were noted between drip and surface irrigation, theokra varieties and the interaction for the rest of the readings expect for the variety in the fourth one. The, DI significant increase can be attributed to the conserved soil moisture, seedling emergence, and improved plant growth which resulted in increased plant height and stem diameter. The mean plant diameter under DI after 90 days from plant growing was 0.81cm while under SI was 0.61cm as shown in Table 8. The increase stem diameter under DI was more than those under SI (Fig. 6) as indicated in results by [23] in the studies of vegetative growth.

   Table 1: Mean monthly meteorological data and mean of reference crop evapotranspiration

   Month	Mean temperature		Relative humidity %	*WS (m/h)	Sunshine (hrs.)	ETo mm/day
   	max	Min
   Nov	36.10	21.50	37	2.11	10.0	7.00
   Dec	32.70	20.40	33	2.11	9.90	6.40
   Jan	29.00	14.90	32	2.37	9.10	6.00
   Feb	31.30	15.90	31	2.60	9.10	6.70
   Mean	32.30	18.80	33.25	2.29	9.53	6.53

   *wind speed at height at 2m.

   Table 2: Okra water requirement

   Month	Nov	Dec	Jan	Feb	Mean
   ETo mm/day	7.00	6.40	6.00	6.70	6.53
   Kc	0.60	0.75	1.00	0.80	0.79
   ETc mm/day	4.20	4.80	6.00	5.40	5.10
   ETc mm/month	126	144	180	162	153

   Table 3: The net crop water requirement (NCWR) for Okra

   Month	ETc mm/month	NCWR (mm/month)	NCWR m3/ha/month
   Nov	126	6.70	6.53
   Dec	144	0.80	0.79
   Feb	180	5.40	5.10
   Feb	162	162	153
   Total	153

   Table 4: Crop WUE of the Okra crop grown under different irrigation systems

   Irrigation method	Yield kg	Total amount of water m3	WUE kg/m3
   DI	17150	581.5	29.49
   SI	11980	920.2	13.02

   Table 5: Variance analysis for plant height (cm) of Okra varieties grown under different irrigation systems

   Source	Df	Days from sowing
   		30	45	60	75	90
   System	1	25.61**	36.26**	1675.61**	3866.43**	3126.64**
   Block/system	2	07.50	10.22	108.85	339.41	0439.03
   Varieties	2	0.83ns	03.35ns	14.87ns	38.09ns	35.05ns
   Varieties × system	2	0.79ns	12.36ns	55.16ns	104.0ns	119.59ns
   Error	4	0.52	11.78ns	08.68	30.11	59.07
   Total	11
   CV %		6.06	13.24	5.85	7.71	9.27

   **: highly significant; ns: no significant.

   Table 6: Plant height (cm) of Okra varieties grown under different irrigation systems

   Treatment	Readings
   	1	2	3	4	5
   DI	13.36	15.68	31.08	44.56	49.51
   SI	10.43	10.22	19.26	24.55	33.37
   V1	12.36	13.49	26.27	37.34	43.13
   V2	11.87	12.75	24.46	31.36	40.37
   V3	11.46	12.61	104.79	34.98	40.83
   DI × V1	13.62	15.44	30.10	43.55	48.15
   DI × V2	13.84	16.32	31.88	45.68	50.63
   DI × V3	12.61	15.27	31.25	44.45	49.70
   SI × V1	11.10	11.53	22.48	31.13	38.10
   SI × V2	9.90	9.18	17.08	17.03	30.05
   SI × V3	10.30	9.95	18.33	25.50	31.95
   Overall mean	11.89	12.95	25.17	34.56	41.44
   LSD* 5 % 4sys	1.02	3.36	4.16	7.75	10.86

   *: LSD: least significant difference.

   Table 7: Variance analysis for stem diameter (cm) of Okra varieties grown under different irrigation systems

   Source	df			Days from sowing
   		30	45	60	75	90
   System	1	0.006ns	0.019ns	0.139**	0.631*	0.371**
   Block/system	2	0.013	0.019	0.031	0.099	0.084
   Varieties	2	0.010ns	0.020ns	0.019*	0.011ns	0.029*
   Varieties × system	2	0.007ns	0.032ns	0.030*	0.365*	0.026*
   Error /td>	4	0.005	0.045	0.003	0.003	0.0002
   CV%		41.21	36.84	3.44	4.69	1.03

   **: High significant difference,*: Significant difference and ns: no significant difference

   Table 8: Interaction of Stem diameter (cm) of okra varieties grown under different irrigation system

   Treatment			Readings
   	1	2	3	4	5
   DI	0.085	0.313	0.491	0.730	0.777
   SI	0.092	0.263	0.383	0.501	0.602
   V1	0.082	0.331	0.457	0.632	0.728
   V2	0.088	0.251	0.398	0.586	0.644
   V3	0.097	0.283	0.458	0.630	0.698
   DI × V1	0.071	0.313	0.468	0.713	0.783
   DI × V2	0.087	0.313	0.450	0.688	0.720
   DI × V3	0.098	0.313	0.555	0.790	0.830
   SI × V1	0.093	0.348	0.445	0.550	0.673
   SI × V2	0.088	0.188	0.345	0.483	0.568
   SI × V3	0.095	0.253	0.360	0.470	0.565
   Overall mean	0.089	0.288	0.437	0.616	0.689
   LSD 5 % 4sys	0.01	0.29	0.074	1.33	0.02

   Fig. 5: Mean plant height (cm) of okra grown under DI and SI systems Fig. 6: Mean steam diameter (cm) of okra grown under DI and SI systems

2. Root length and weight

   The results showed no significant difference between DI, SI, varieties of okra and interaction (varieties×system) for the length and weight (Table 9). This indicates that okra plant growth needs higher soil moisture. Fig 7 shows the length and weight of root zone was marginally under SI than DI system for the three varieties of okra. Different studies have shown significant relationship of different irrigation supply with root length, which triggers the accumulation of dry matter to the roots. Roots are in direct contact with soil and the first to be affected by the water logging. Thus growth is not faster under the SI, this system and result is in line with findings of [24], [22], [25].

3. Yield (kg/ha)

   The results of yield for the nine picks, showed a significant difference in picks 1, 3, 5, 7, and 9 among the irrigation systems, the okra varieties and their interaction (system ×varieties). However, there were no significant differences in picks 2, 4, 6 and 8 for both irrigation systems and okra varieties and the interaction. This may be caused by variations of water requirements of okra are due to the nature of cultivars studied under the different methods. Referring to (Table 10) the increase in yield for all readings was more in the DI compared to the SI (Fig. 8). Similar results were obtained by [26]. [27] Stated that the highest fruit yield could be ensured with moderate intensity of irrigation. The increase in yield when using DI was 220.18, 1322.15 and 290.12% for V1, V2 and V3 respectively of that under SI. These results indicate that okra varieties (V1, V2 and V3) are suitable for improvement through selection in the study [28]. The overall mean yield for DI was 249.71 kg/ha, and that for SI was 155.65 kg ha-1. Many studies reported on different crops irrigated by the drip and furrow

   Table 9: Variance analysis for Root length (cm) and weight (g) of okra grown under two different irrigation systems

   irrigation methods in different parts of the world found that yield and WUE is higher with drip irrigation in comparison with furrow irrigation [29], [30], [31].

   Fig. 7: Root length (cm) and weight (g) of Okra varieties grown under two different irrigation system

   Fig. 8: Mean yield (kg/ha) of okra grown under DI and SI systems

   Treatments	Mean square	Observed F	Required F
   			5 %	1 %
   Root length (cm)	85.336	0.137ns	7.71	21.20
   Root weight (g)	157.6875	0.619ns	7.71	21.20

   Table 10: Yield (kg/ha) of interaction between okra varieties grown, DI and SI systems

   Treatment	Number of picks
   	1	2	3	4	5	6	7	8	9
   DI	155.41	58.06	70.99	58.06	83.83	112.86	313.48	187.51	249.71
   SI	32.25	44.09	60.84	44.09	48.85	135.97	212.81	163.99	155.65
   V1	84.363	65.5	63.61	65.50	74.91	103.08	300.41	186.22	163.28
   V2	86.23	43.82	56.58	43.81	65.72	156.12	261.28	163.81	199.06
   V3	110.89	43.91	77.54	43.92	58.41	114.06	227.75	177.22	245.68
   DI × V1	128.57	61.00	86.31	61.00	85.31	112.66	341.13	192.16	127.75
   DI × V2	161.13	65.69	43.00	65.69	89.69	89.69	370.06	170.00	274.38
   DI × V3	176.53	47.50	83.65	47.50	76.50	136.25	229.25	200.38	347.00
   SI × V1	40.156	70.00	40.91	70.00	64.50	93.50	259.69	180.28	198.81
   SI × V2	11.33	21.94	70.16	21.94	41.75	222.56	152.50	157.63	123.75
   SI × V3	45.25	40.32	71.44	40.32	40.31	91.25	226.25	154.06	144.38
   Overall mean	93.828	51.08	65.91	51.08	66.34	124.37	163.15	175.75	202.68
   LSD 5 %	64.24	31.83	87.66	285.5	57.68	168.50	109.80	98.94	360.95
   CV%	24.2	22.05	5.99	41.50	30.8	56.9	14.76	19.92	20.7

   1. CONCLUSION

Different methods of irrigation play a significant role in okra production. Thus, to maximum land utilization and water as well as production of okra calls for an effective irrigation system. The study revealed better plant growth, high water use efficiency and enhancement in the yield under drip irrigation as compared to the furrow irrigation method.

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