Dry Season Irrigated Rice Yields Response to Water Saving Techniques in Tolon District of Northern Region, Ghana

Shaibu Abdul Ganiyu^1*, Naoko Oka² and Seiji Yanagihara^2
*Correspondence: Shaibu Abdul Ganiyu, Department of Engineering, University for Development Studies, Tamale, Ghana, Tel: 233243888331, Email:

Keywords

Dry season irrigation • Rice • Water-saving • Water saving methods

Introduction

Nearly half of the world’s population (2.7 billion people) depend on rice as the staple food as it provides 35–60% of the calories consumed [1]. Worldwide, the agricultural sector makes the largest demands of any sector on our finite fresh water resources, and within this sector, irrigated rice production is the largest source of demand for fresh water [2].

Rice is the staple crop for more than half of the world’s population. It is the most important crop grown in Asia, providing livelihoods for millions of farmers, and up to 70% of calories for the poorest people across the region. Roughly 90% of the world’s rice is grown in Asia, and most of it is consumed there [3].

Rice consumption patterns and levels in Ghana have undergone a rapid transformation. Annual per capita rice consumption increased from 24 kg in 2012/13 to 35 kg in 2016/17 (GSS 2018); moreover, whereas per capita expenditure on rice was 3.3 times that of maize in 2012/13, this increased to 4.1 by 2016/17 [4]. Urban consumers account for 70 percent of national consumption. Both rural and urban households reveal a preference for long grain aromatic varieties, which are mostly imported [5]. Paddy rice production in Ghana has increased steadily at 11.1 percent per annum since 2008. Production reached 963,000 tons in 2019 (equivalent to 665,000 tons of milled rice). At 6.9 percent per annum, the expansion of area cropped with rice was an important driver of output growth; by contrast, yields grew at 4.5 percent per year [6]. However, Irrigated rice production requires large amounts of water, with 1 kg of rice grain requiring 2500 L of water [7]. According Chapagain and Hoekstra, in the period 2000-04, the global average water footprint of paddy rice was 1325 m3/ton (48% green, 44% blue, and 8% grey), which is much lower than previous estimates. There is about 1025 m³/ton of percolation in rice production. The global water footprint of rice production is estimated to be 784 billion m³/yr.

Although Ghana has an abundance of water from rainfall, this resource is very unevenly distributed, both geographically and seasonally. Irrigation is needed to ensure crops have water during the long dry season. If well managed, Ghana’s surface water and groundwater systems are able to meet most domestic and irrigation needs. But the lack of installed water infrastructure provides a serious constraint to irrigation development [8]. Rice and vegetables dominate the small irrigated crop sector of Ghana with close to 190 000 hectares of paddy rice and 77 000 hectares of vegetables. About 11% of all paddy rice production is irrigated with flood irrigation (20000 hectares) resulting in loss of the scarce water resources [9].

Given the following trends, making substantial, not just marginal reductions in on-farm water consumption in rice farming will have farreaching effects in saving water for other water consumptive demands in the irrigated agricultural sector of Ghana.

One of the methods to save water in irrigated rice cultivation is the intermittent drying of the rice fields instead of keeping them continuously flooded. This method is referred to as Alternate Wet/Dry irrigation (AWD). AWD can lower water use for irrigated rice by ~35%, increase rice yield by ~10% relative to permanent flooding [10].

The other ways to save water in rice cultivation is using the System of Rice Intensification (SRI) water management regime. According to Uphoff and Randriamiharisoa, the System of Rice Intensification (SRI) methodology, developed by Fr. Henri de Laulanié over two decades of observation, experimentation and innovation in Madagascar, shows that keeping paddy soils moist but not continuously saturated gives better results, both agronomically and economically, than flooding rice throughout its crop cycle.

The research therefore assessed the effects of water management of AWD and SRI as compared with continuous flooding on saving of water and rice yields for dry season in golinga irrigation scheme in the tolon district of northern region, ghana.

Materials and Methods

Study area

The field experiment was carried out at the golinga irrigation scheme in the Tolon District of Northern Region of Ghana. The Scheme is located 14.5 km south west of Tamale the regional capital. It lies on latitude N09.35845° and longitude W000.95317°. The study area has an average rainfall of 1060 mm and average seventy-seven (77) rainy days in a year with 87% of the total annual occurring from May to October. The relative humidity ranges from 15% low in January to highest 82% in August. The wind speed is the lowest in November of 72 km/day and highest in April of 225 km/day. The sunshine duration is highest in November with 8.8 h/day and lowest in August of 4.9 h/day [11]. The relief of the area is fairly flat and gentle slopping towards the reservoir. The watershed landscape pattern is mosaic and has a leutic system where it drains into the reservoir. Generally, the Golinga watershed is characterized by grasses with few scattered economic trees. The predominant soil types in the area are loamy sand and sandy loam.

The Golinga reservoir has full supply level of 139.25 m asl, dam length of 1.2 km, maximum storage capacity of 1243.254 m³, minimum storage capacity (dead) of 99.939 m³, useful storage capacity (live) of 1,143.315 m³ and full supply level of 81.25 ha. The catchment area of the Golinga river basin is 21.36 km². The potential area of the irrigation scheme is 100 ha, whiles the developed area is 40 ha.

Soil physical properties

Before the experiment was conducted, soil infiltration test was carried out on 9^th January 2018 in the experimental site to determine the infiltration rate of the soils. The tests were conducted at upstream, midstream and downstream of the experimental site using the Decagon Mini-disc infiltrometer.

Soil chemical properties

Composite soil samples (0–30 cm depth) of the site were collected on 9^th January 2018 and analysed for texture, Soil pH (H₂O), Organic carbon content as well as Nitrogen (N), Phosphate (P) and Potassium (K), magnesium, calcium, electrical conductivity and salinity.

The two years dry season experiments on rice at golinga irrigation scheme for the 2017/2018 and 2018/2019 farming seasons were conducted using complete randomised block design (Figure 1) and Figure 1 by applying five water regimes as the treatment and with each replicated 4 times in four blocks. The foundation seeds, Jasmine 85 rice variety, were obtained from the Savannah Agricultural Research Institute (SARI) in Tamale for the experiment. The treatments are as follows:

• SRI with soil moisture content maintained at Field Capacity (FC)

• AWD 15, if 1 to 10 cm of standing water above the soil drop to 15 cm below the soil surface

• AWD 10, if 1 to 10 cm of standing water above the soil drop to 10 cm below the soil surface

• AWD 5, if 1 to 10 cm depth of standing water above the soil drop to 5 cm below the soil surface

• CF, Continuous flooding at 1 to 10 cm depth of water depending on the growth stages of rice (Table 1).

Field instrumentations and observation: As seen in Figure 1, the following instruments were planted in the plots to monitor soil moisture and temperature at the various growth stages of the crop.

Volumetric soil moisture contents at the depth of 20 cm were measured throughout the growing period by EC-5 soil moisture sensors and Em5b data loggers, decagon devices.

Soil temperature was also monitored throughout the growing period at the depth of 6 cm using TR 52i soil temperature sensors. The sensors were installed in the centre of plots at the depth of 6 cm at planting.

Tensiometer: A total of 5 manual tensiometers were installed in some of the plots with the exception of CF plots to monitor soil moisture potential up to 20 cm depth of the root zone.

Groundwater tube: Six (6) groundwater tubes made of 5 cm diameter PVC pipe, 200 cm long, with perforation (0.5 cm diameter) in the bottom 50 cm were installed in the continuous flooding and intermittent flooding plots to monitor water table fluctuations by observation using water level monitoring sensor tape and HOBO water level sensor.

Field water tube: 8 field water tube made of PVC pipe with a length of 30 cm and diameter of 20 cm were installed in the AWDI plots to monitor the irrigation water depth using ruler.

Water application rate for treatments: The depth and volume of water applied to each plot (3 m x 7.5 m) based on the water application regimes (AWD 10, AWD 15, CF, AWD 5 and SRI) and the growth stages of rice in the experiments for the two years are presented in Table 1. Water application was done using 2 inches Automatic Metering Valve (AMV): 2 automatic metering valve was connected to a 2 gasoline pump to deliver required quantity of water to the plots. This helped to calculate the total water consumed by each treatment (Table 2).

Soil physical and chemical analyses

The composite soil samples of the site were analysed for texture, Soil pH (H₂O), organic carbon content as well as Nitrogen (N), Phosphate (P) and Potassium (K), magnesium, calcium, electrical conductivity and salinity. The analysis was done at Savannah Agriculture Research Institute’s Soil Laboratory in Nyankpala. Soil physical properties such as Field Capacity (FC), Permanent Wilting Point (PWP) and Saturation moisture contents, porosity, infiltration rate, hydraulic conductivity and bulk density were also measured.

Nursery for rice seedling

The nursery for rice seedlings were established closer to the experimental site on the 20^th January, 2018 and 05^th February, 2019 respectively for the two seasons using jasmine 85 rice variety. The seedlings were ready for transplanting after one month.

Land preparation for transplanting

Land preparation was done by using tractor with disc plough and harrow to get good seed bed for the rice. After ploughing the field was demarcated into plots with earth bunds of 30 cm bottom width, 20 cm top width and 15 cm height.

Transplanting

Transplanting of rice seedlings were done on 19^th February 2018 and 8^th March 2019 respectively for the two seasons with one seedling per hill at spacing of 20 x 20 cm row planting.

Plant growth observation

The plant height and tillers were monitored at week-4, week-6, week-8, week-10 and week-12 which represent the various stages of the rice growth.

Yield sampling: 2.4 m x 2.4 m in the middle of each plot was done to determine the grain yield, grain quality, and sterility. Yield components and aboveground biomass were also determined by taking average-sized 6 plants from the plot.

Record of flowering date was done at 50% flowering.

Chlorophyll content was measured using SPAD-502 (Konica Minolta).

Application of compound fertilizer

Basal application of NPK (23/10/05) at 70 N kg/ha to all the plots were done on 28^th/02/18 and on 30/03/19 respectively for the first and second seasons after the fields had been drained. The quantity applied was 685 g/plot (22.5 m²) based on calculation.

Application of sulphate of ammonia

Following the application of compound fertilizer, the application of Sulphate of Ammonia (Ammonium Sulphate=21-0-0-24 S) at 50 kg/ha was done at panicle initiation stage (26^th April, 2018) and (22^nd May, 2019) respectively for the 2018 and 2019 dry seasons after draining the fields. The quantity applied to each plot was 531 grams based on calculation.

Data analysis

Each treatment was harvested separately and put in a sack to avoid mixing with other treatment. The harvested rice was threshed in a controlled environment to avoid contamination and loss of paddy. After threshing the fresh weights were taken and moisture content determined using grain moisture tester (PM-450) for adjustment of the weight to 14% moisture content. The yield related parameters such as weight of 1000 g seed, percent filled, fresh and dry stock weights, among others were also measured. The data were organised in Excel spreadsheets and analysed using GenStat Discovery Edition.

Results and Discussion

Soil physical properties

Table 3 presents the soil physical properties of the experimental site. The texture of the top soil is sandy loam with high sand percentage averaging 64.15% and low clay content also averaging 8.9%. This characteristic of the top soil result in low water holding capacity (field capacity and available water capacity) at 0-30 cm depth of soil. This result is in line with the assertion by Senayah, et al. that, within the drier Savannah agro-ecological zones, lowland soils are relatively low in clay content. Most locations show less than 10% clay content. The soils are generally deep but water retention capacity may be low due to low clay contents [12]. The bulk density of the soil was slightly high due to compaction through paddling.

The last column of Table 3 presents the results of the infiltration rate of the soils. The top soil is sandy loam along the slope, the rate of infiltration of the soil, which ranges from a minimum of 14.9 mm/h to a maximum of 25.8 mm/h, suggest that the soils are well drained at the surface.

Soil chemical properties

Tables 4 and 5 present the chemical properties of the soil. As seen in Table 4, the acidity (pH) of the soil was relatively low with a mean of 6.1 which also results in relatively low exchangeable acidity (Table 5). The pH of the soil was in the range of moderately to slightly acidic [13]. These conditions have not adversely affected basic cation balances particularly Ca and Mg as such, rice growth in the valley is not also affected.

However, the soils have very low organic carbon and organic matter content due to burning of crop residue after every harvest. The very low values have confirmed the assertion by Senayah, et al. that, within the Savannah agro-ecology, organic carbon levels are comparatively lower. This could be attributed to continuous cropping and burning.

Similarly, the total nitrogen levels are also very low and conformed with the assertion by Senayah, et al., that the Savannah zones show much lower levels of total nitrogen with much lower variability compared to the forest ecology. This suggest that, the soil required more nitrate fertilizer to be productive.

Like the other chemical properties, the Phosphorus (P) level of the soil is also very low with a mean value of 6.39 μg/ml. These results are in line with the findings by Buri, et al. that available P is generally very low for all the soil types and across all agro-ecological zones in Ghana. Available P is the single most limiting nutrient. Within the Savanna zones, mean available P levels for lowlands is even lower with mean level of about 1.5 mg kg^-1. This suggested that more quantities of Single Super Phosphate would have to be applied to augment the low quantities.

The exchangeable base of the soil in the experimental area is low as seen in Table 5. As seen from the Table, means of Calcium (Ca) and Magnesium (Mg) are 1.88 Cmol (+)/Kg and 0.52 Cmol (+)/Kg respectively. According to Senayah, et al., exchangeable cation levels within the savannah agro-ecological zones are generally low when compared to those of the forest agro-ecological zone. Topsoil exchangeable calcium is 1.76-2.24 cmol (+) kg^-1 for the lima series (Planosols). Mean level of exchangeable Mg (0.9 cmol (+) kg^-1) and mean levels of exchangeable K (0.22 cmol (+) kg^-1) are quite low.

In terms of salinity, the soil of the experimental site was less saline, since the level of EC was less than 2 dS/m.

Average plant height at maturity

The plant height (Table 6) was monitored at week-4, week-6, week-8, week-10 and week-12, of the rice growth. From the Table, plant height for AWD 10, AWD 15 and CF indicated highly significant difference with SRI throughout the growth period of the rice crop for both year 1 and year 2, as well as their average at maturity stage. The difference in plant height between SRI and the rest of the treatments could be attributed to the least amount of water applied to SRI resulting in the shortest plant height as compared to the rest of the treatments. According to Zeigler, et al., rice is extremely sensitive to water shortage and that, the growth of the plant is prevented and the size of the various plant parts decrease with water shortage below saturated soil moisture content. According to Zulkarnain, et al. the tallest plant was observed in the rice grown under flooded condition, with rice growth under saturated and flooded conditions comparable, as was the case for maintaining the soil at AWD 5, AWD 10, and AWD 15 condition in these experiments. These findings are in line with the assertion by Datta that, application of water at higher regimes promoted growth of rice by increasing plant height.

Values within each column followed by a common letter are not significantly different (p=0.05)

Tiller count at maximum tiller

Table 7 shows the analysis of tiller count at the maximum tiller for the two-year on-farm experiments. The effect of irrigation regime on maximum tiller count of rice grown under SRI, AWD 15, AWD 10, AWD 5 and CF for year one and two experiments showed no significant difference when their means were compared, with the LSD values. According to Zoundou, et al., tillers number is a determinant of yield when assumed that every tiller bears a panicle. From the table, it could be observed that at maximum tiller, all the treatments gave almost similar number of tillers, which could be attributed to reduction in water application rate (2-5 cm depth of water at 8^th week) at that stage like the SRI that boosted tillering. According to Surajbhan, irrigating rice at saturation during tillering and panicle initiation stages gave better results than irrigating at saturation during other stages; this could probably be due to adequate circulation of oxygen around the root zone depth. These findings are coherent with that of according to whom, averages of 20–30 tillers per plant are fairly easy to obtain and in some well-managed fields 50, even 70 tillers per plant [14].

Values within each column followed by a common letter are not significantly different (p=0.05)

Average chlorophyll content at maturity

The chlorophyll meter (SPAD) was used to measure the chlorophyl content at various stages and at maturity for the 2018 and 2019 dry seasons. Even though the SPAD values did not show any significant difference between SRI and the rest of the treatment at <0.05 for the 2018 and 2019, their treatment mean, shows significant difference between SRI and both CF and AWD 5. However, by comparing the means of each year with their LSD values for the two years indicate significant difference between SRI and IF as can be seen in Table 8. With reference to the table, AWD 5 recorded the highest SPAD value followed by CF, whiles SRI recorded the least value. Ghosh, et al. estimated the optimal SPAD threshold for rice as 37.5. This suggest that, the values obtained from these experiments are lower, indicating low chlorophyll content, hence low nitrogen content from the soil for the crop.

Values within each column followed by a common letter are not significantly different (p=0.05)

Days to 50% heading

Table 9 presents the results of days to 50% heading. From the two-year analysis of on-farm results, days of 50% heading after transplanting indicated significant difference between SRI and the rest of the treatment (CF, AWD 5, AWD 10 and AWD 15) when their means were compared using LSD values. From Table 9, it could be seen that SRI gave on the average, the highest value for days to 50% heading (78 days), whiles the rest of the treatments gave the lower values, 67.75 to 71 days. However, the grand means of 2018 and 2019 as well as the overall mean of the combined years gave at least 70 days as number of days spent at 50% heading. According Davatgara, et al., water stress decreased yield and increased the delay of 50% flowering in day at mid-tillering and booting stages as compared to well-watered plants.

Values within each column followed by a common letter are not significantly different (p=0.05)

Average panicle dry weight (g)

Table 10 shows the results of analyses for panicle dry weight for both years and their combined means. From the Table, it could be observed that, panicle dry weight showed significant difference between SRI and the rest of the treatments when the means were compared using LSD values for both years. The SRI indicated the lowest while AWD 10 at 2019 gave the highest value for panicle dry weight. It could be observed that increase in number of tillers resulted in increase in photosynthetic rate of the various treatments, thereby producing high panicle dry weight and hence increase in grain yield.

Values within each column followed by a common letter are not significantly different (p=0.05).

Unfilled grains percentage (%)

Table 11 shows the results of analyses for unfilled grain percentage for both years and their combined means. From the Table, it could be observed that, unfilled grain percentage showed significant difference between SRI and the rest of the treatments when the means were compared using LSD values for both years. The SRI indicated the highest while CF gave the lowest value for unfilled grain percentage. These results are in accordance with those reported by Pirmoradian, et al. indicating that, water stress caused increase in percent of unfilled grains.

Values within each column followed by a common letter are not significantly different (p=0.05)

Average mass of 1000 grains (g)

Table 11 shows the results of analyses for mass of 1000 grains for both years and their combined means. From the Table, Like the unfilled grain percentage, it could be observed that, mass of 1000 grains showed significant difference between SRI and the rest of the treatments when the means were compared using LSD values for both years. The SRI indicated the lowest while the rest of the treatments gave highest values for mass of 1000 grains. The nature of the results of the 1000 grains mass are in line with the assertion by Uppal, et al. that, application of water at higher regimes promoted growth of rice by increasing higher 1000 grains weight.

Values within each column followed by a common letter are not significantly different (p=0.05)

Biomass and grain yields

Table 13 and Table 14 show the results of analyses for above ground biomass and grain yield for both years. From the Tables, it could be observed that, above ground biomass and grain yield showed significant difference only between SRI and the rest of the treatments when the means were compared using LSD values for both parameters. The SRI indicated the lowest while AWD 5 the highest value for biomass; however, in terms of grain yields, CF gave the highest yields followed by AWD 10, AWD 5 and AWD 15. Theresults therefore suggested that, maintaining rice plants at an alternative wet and drying or intermittent flooding condition throughout the growing period has resulted in a significant increase of the total biomass and rice yields respectively (Table 13). It could be observed that increase in number of tillers resulted in increase in photosynthetic rate by producing high biomass, 1000 grain weight and hence, increase in grain yield. The lower yield for rice grown under SRI condition was therefore mainly due to water stress at booting and anthesis and less shoot dry weight as reported by Grigg, et al. SRI which is a practice of rice cultivation under conditions of relatively severe shortages of irrigation water is referred to as “aerobic rice” [15]. The paddy soil remains aerated (aerobic) throughout the rice-growing cycle. The practice aims at keeping the soil “wet” but not flooded or saturated [16-18].

Values within each column followed by a common letter are not significantly different (p= 0.05)

Values within each column followed by a common letter are not significantly different (p=0.05)

Soil temperature

Figure 2 presents the average soil temperature variation of the experimental site between March and June 2018 and 2019. The average soil temperatures were within the range suitable for rice cultivation as the highest value was even less than 35°C and the lowest temperature was 26°C. From the graph it could be observed that soil temperature was not stable but kept fluctuating, which could be attributed to soil moisture variation [19,20]. This suggests that none of the treatments produce temperature conditions that are not suitable for rice cultivation. According to temperature, along with photoperiod, is the main driving force for crop development. The optimum temperature for the normal development of rice ranges from 27 to 32°C [21-24]. High temperature affects almost all the growth stages of rice, i.e. from emergence to ripening and harvesting. The developmental stage at which the plant is exposed to heat stress determines the severity of the possible damage to the crop [25-28].

Total water applied, grain yield and amount of water saved: Presents the volume of irrigation water applied to the various treatments in 2018, 2019 and their average, the average grain yield as well as the percentage of water saved relative to CF. The average volume of water consumed by the rice varied from a minimum of 2880.76 m³/ha corresponding to 2.8 t/ha for SRI to a maximum of 5921.74 m³/ha corresponding to 4.8 t/ha for CF, given a yield gap of 2 t/ha (41.7%). However, in terms of water saving, SRI saved the highest (45.79%) whilst AWD 5 saved the least when compared with Continuous Flooding (CF) (Table 15).

Soil moisture characteristic curve for the treatments: Figures 3-8 shows the soil moisture characteristic curves for the five water management regimes and their average [29,30]. All the graphs indicate that, as soil moisture increases soil tension reduces and the vice-versa. The moisture content for all the treatments were within the readily available moisture regimes of field capacity and saturation. Apart from SRI which suffers more water stress as it reproductive stage was with the field capacity moisture regime throughout; the other treatments were well within the varying ranges of field capacity and saturation or flooding conditions. From the graphs it could be observed that CF, AWD 5, AWD 10 and AWD 15 are all within the range of 0-10 kPa: Saturation (0 kPa) to near saturation; whiles SRI is within the moisture range of 10-30 kPa: Field capacity [31-35].

Conclusion

• There was significant difference between SRI and the rest of the treatments in terms of rice grain yields and yield related parameters

• Soil moisture tension, even though was fluctuating with respect to changes in the moisture regimes of the soil due to the treatment effects, the severity of the tension was with SRI resulting in low yields

• Soil temperatures were in the range suitable for rice cultivation

Recommendations

Even though CF yielded the highest, it is recommended that intermittent flooding (AWD 5 and AWD 10) are introduced to small, medium and large scale or commercial farmers since they have optimum yields.

Acknowledgements

This research was carried out by the Department of Agricultural Engineering of School of Engineering, University for Development Studies in collaboration with the Japan International Research Center for Agricultural Sciences (JIRCAS).

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