The most limiting factors for irrigated rice farming are water and nitrogen. Efficient water and nitrogen management has remained critical for sustainable rice production in irrigated rice farming system. Due to rapid global population growth and climate change, future rice production will depend heavily on developing strategies and practices that use water and nitrogen efficiently. The study therefore set to evaluate agronomic, water productivity and economic analysis of irrigated rice under various nitrogen and water management methods. To achieve the set objectives, field and pot experiments were carried out at the Soil and Irrigation Research Centre, University of Ghana, Kpong in 2015 and 2016 cropping season. The field experiment was laid in a split plot design with water management treatments as main plots and N fertilizer as subplot treatment. The pot experiment was carried out in a randomized complete block design with five replications. The water management treatments were; continuous submergence (SC), alternate wet and dry soil condition (AWD) and moist soil condition (MC). Nitrogen fertilizer rates were; no N fertilizer (N0), 60 kg N/ha (N1) and 90 kg N/ha (N2). Data such as yield and yield parameters of rice, water use, water productivity, costs and returns were recorded. Results obtained from both pot and field experiments revealed that rice yields were at par in AWD and SC but yields were lower in MC treatment. With N fertilizer, higher yields were observed with 90 kg N/ha. The interaction effect of submerged with 90 kg N/ha gave the highest grain yield. N fertilizer effect on water use and water productivity was ranked as N2 > N1 > N0 while water management effect on water use and water productivity was ranked in this order: SC > AWD > MC and MC > AWD > SC respectively.
Rice (Oryza sativa L.) is one of the most consumed cereal crop in most of parts of the world. It is said to be a staple crop for more than half of the world’s population [
The rice sector is not only the major contributor of food security but also the biggest consumer of freshwater resources. Researchers [
It is widely acknowledge that rice is grown under continuous submergence to counter nutrient, water and weed stresses by pumping water from the rivers and their tributaries by either small diesel pumps or large electric pumping systems which intern reduce water productivity and farmers’ income [
Also, N nutrition drives rice production but there is a spiral increase (50%) in inorganic fertilizer prices in Ghana due to fall of the local currency on exchange market, increase in fuel prices and the removal of government subsidies on fertilizer price [
Furthermore, decreasing water availability for agriculture threatens the production of rice in irrigated system. Worldwide, fresh water resources are threatened by rapid global population growth and climate change. Due to growing demand for water resources from all sectors, it is projected that by 2025, some countries in Sub-Sahara Africa (SSA) including Ghana will face water stress [
In order to improve water use efficiency and water productivity in irrigated rice, many water management techniques have been proposed [
The experiments were carried out at the Soil and Irrigation Research Centre (SIREC) of the University of Ghana in 2015 and 2016 cropping season. Geographically, the experimental area is located between latitudes (00'04''E, 60'09''N), in the Eastern region of Ghana. It is part of the Accra plains and has annual rainfall between 800 and 1100 mm with mean annual temperature of 28˚C. The soils of the experimental site are vertisols, which are characterised by montmorillonitic clay minerals with clay content of 35% - 40%. Initial chemical characteristics of soils of the experimental site (0 - 20 cm depth) are indicated in
The land was prepared by ploughing to bury all vegetation, submerged with water and puddled to reduced percolation of water. Experimental units of 2 m × 3 m were measured out using a measuring tape, garden line and pegs. Sixty (60) cm high metallic barriers were inserted in each unit at a depth of 30 cm to prevent lateral movement of nutrient and water in and out of the plots. The size of each of the metallic containers was 2 m × 3 m and they were sprayed with anti-rust paint to prevent rusting.
For the pot experiment, plastic pots with 10,000 cm3 volume were used. Soil was collected from an uncultivated field at a depth of 0 - 15 cm and was crushed and sieved through 2 mm size mesh to obtain fine earth fraction. Nine kilograms (9 kg) of the soil was weighed into each plastic pot to attain the field bulk density. The pot experiment was carried out in a randomized complete block design with five replications.
The experiment was carried out in a split plot design with 3 replications. The main plot factors were water management regimes and the sub-plot factors were nitrogen levels. The three water management methods were: alternate wet and dry (AWD), moist soil condition between field capacity and permanent wilting point (MC), and continuous submergence (SC). The nitrogen levels were: 0, 60 and 90 kg N/ha as subplots within each main plot as indicated in
Depth (cm) | TN% | AP | AK (mg∙kg−1) | Ca (mg∙kg−1) | pH | OC% |
---|---|---|---|---|---|---|
0 - 20 | 0.067 | 2.09 | 4.72 | 22.83 | 7.55 | 1.55 |
TN: total nitrogen, AP: available phosphorus, AK: available potassium, Ca: exchangeable calcium, pH: soil reaction, OC: organic carbon.
Water management | Nitrogen fertilizer level |
---|---|
No nitrogen fertilizer (N0) | |
Alternate wetting and drying (AWD) | Urea 60 kg N/ha (N1) |
90 kg N/ha (N2) | |
No nitrogen fertilizer (N0) | |
Moist condition between saturation and field capacity (MC) | 60 kg N/ha (N1) |
90 kg N/ha (N2) | |
No nitrogen fertilizer (N0) | |
Continuous submergence (CS) | 60 kg N/ha (N1) |
90 kg N/ha (N2) |
metallic barriers of size 6 m2 were then buried 30 cm deep in each sub plot to reduce lateral movement of water and nutrients. Rice variety, Ex Baika was used as the test crop. Twenty five days old seedlings were transplanted at spacing of 20 cm within rows and 20 cm between rows with 2 seedlings per hill. During planting, all the plots were kept saturated with irrigated water to prevent transplanting shock.
The nitrogen fertilizer source was Urea. Nitrogen fertilizer was applied two times that is 50% at transplanting and 50% at panicle initiation. Nitrogen fertilizer levels were 0, 60 and 90 kg N/ha henceforth referred to as N0, N1 and N2, respectively. Straight fertilizers of triple Superphosphate (P2O5) and muriate of potash (K2O) was applied at a rate of 45 kg/ha to all the plots at transplanting of seedlings.
After transplanting, all the plots were irrigated to maintain uniform moisture content at saturation for the first week to ensure full establishment of the seedlings. Perforated PVC pipes of about 3 cm in diameter and 45 cm in length were inserted in all except submerged treated plots 15 cm above and 30 cm below the soil surface to monitor soil water levels below the soil surface.
Graduated buckets and cylinders were used to apply water to the plots and pots, and the quantity of water applied throughout the experiment was recorded. The amount of rainfall (rainfall events) during the experimental period was also recorded. A metre wooden rule was used to measure moisture level below and above the soil surface. Water was maintained at 5 cm above the soil surface till ten days to harvest in the continuous submerged treatment. For the moist treatment, soil moisture was kept at 18 cm and 25 cm below the soil surface in the pot and field experiments, respectively. In the AWD treatment, the experimental unit was only submerged (5 cm above the soil surface) when soil moisture dropped to 18 and 25 cm below the soil surface in the pots and field experiments, respectively. All the treatments were continuously submerged at booting stage to ten days to harvest.
Water was applied through a horse pipe and the amount of water consumed per plot was measured using containers with known volume. Water application was done using graduated containers (10 and 15 liters). The amount of water-use was obtained from daily measurements. Depth of irrigation water (mm) applied was computed by dividing the volume of water applied by the area of the subplot. Also, amount of precipitation during the period (rainfall events and amounts) were recorded.
Grain yield was determined by weighing grains from 5 m2 and expressed as t/ha at 14% grain moisture. Ten plants were selected at the center of the plot randomly and used to determine the yield components: test weight, percentage of filled grains, grains/panicle and effective tillers.
Quantification of water productivity and economic analysis of water use
Water productivity was estimated according to [
W P = G Y T W A
where; WP = water productivity (kg/m3), GY = grain yield (kg/ha) and TWA = total water applied (irrigation water and rain water) expressed in m3/ha. Percentage water saving was obtained with reference to the irrigation water and calculated as the difference in irrigation under the two water management regimes divided by the irrigation water applied under the SC regime expressed as a percentage.
Net returns from sales of rice was calculated as;
Net returns = Cost of production − Gross returns (1)
Benefit cost ratio; B/C was estimated using the formula;
B / C = Gross returns Cost of cultivation (2)
Data collected were subjected to analysis of variance (ANOVA) to find out the significance difference due to treatments using GenStat (12th Edition). Mean separation was done using least significance difference (LSD) at 5% level of significance.
The summary for the climatic data presented in
Grain yield was significantly (p < 0.05) influenced by water management and N fertilizer (
Number of effective tillers/pot was significantly (p < 0.05) influenced by both water management and N fertilizer (
Number of effective tillers increased with increased N rate with the lowest number of tillers being recorded in plants treated with no N fertilizer (N0). Interaction effect of N2 and SC produced higher number of effective tillers followed by N2 and AWD interaction. In all, N0 with MC interaction was inferior to all other interaction effect. Number of grains/panicle was significantly (p < 0.05) influenced by water management and N fertilizer (
AWD and SC produced similar number of grains/panicle however, MC treated plants produced the lowest number of grains/panicle. With response to N fertilizer, number of grains/panicle increased with increased N application rate with the lowest number produced in N0. Interaction effect of N2 with SC and N0 with moist produced the highest and lowest number of grains/panicle respectively.
Percentage filled grains ranged from 88.3% to 93.7% depending upon treatment combination as indicated in
Month | Rainfall (mm) | Maximum temperature (˚C) | Relative humidity (%) |
---|---|---|---|
July | 97.0 | 31.0 | 37.4 |
August | 22.3 | 31.0 | 34.9 |
September | 21.9 | 32.2 | 59.0 |
October | 106.4 | 32.6 | 62.0 |
November | 96.0 | 33.8 | 60.2 |
December | N/A | 34.2 | 23.0 |
January | 33.2 | 34.7 | 34.7 |
N/A: not available. Source: Agrometeorological station, SIREC-Kpong.
Parameter | Water mgt. (W) | Nitrogen management (N) | LSD (0.05) | |||||
---|---|---|---|---|---|---|---|---|
N0 | N1 | N2 | Mean | N | W | N × W | ||
Effective tillers | AWD | 15 | 20 | 21 | 19 | |||
MC | 12 | 14 | 18 | 14 | 0.9** | 0.9** | 1.6* | |
CS | 15 | 19 | 22 | 19 | ||||
Mean | 14 | 18 | 20 | |||||
Grains/panicle | AWD | 100 | 106 | 134 | 113 | |||
MC | 91 | 95 | 102 | 99 | 4.1** | 4.1** | 7.1* | |
CS | 103 | 108 | 135 | 115 | ||||
Mean | 98 | 103 | 124 | |||||
% filled grains | AWD | 89.3 | 93.7 | 92 | 91.7 | |||
MC | 88.3 | 89 | 90 | 92.6 | 1.3* | ns | ns | |
CS | 91.7 | 93.7 | 92.3 | 89.1 | ||||
Mean | 89.8 | 92.1 | 91.4 | |||||
1000 grain weight (g) | AWD | 27.4 | 26.9 | 26.5 | 26.8 | |||
MC | 27.1 | 26.6 | 27.1 | 26.9 | ns | ns | ns | |
CS | 27.3 | 27.5 | 27.4 | 27.4 | ||||
Mean | 27.3 | 27 | 27 |
AWD: alternate wetting and drying soil condition; MC: moist soil condition between field capacity and permanent wilting point; CS: continuously submerged soil condition; N0, N1 and N2, are 0, 60 and 90 kg∙N∙ha−1 respectively. LSD: least significant difference; * means significant at 5%; ** means significant at 1%; NS means not significant at 5%.
(p < 0.05) influenced by N fertilizer treatments but not by water management. N2 and N1 did not differ in percentage filled grains but lowest percentage filled grains was recorded in N0. The interaction of water management and N fertilizer on percentage filled grains was non-significant (p > 0.05).
Test weight was not significantly (p > 0.05) influenced by both N fertilizer and water management (
Water use was significantly (p < 0.05) influenced by both water management and N fertilizer application rate (
Nitrogen did not significantly (p > 0.05) influence percentage of water saved. Also there was no significant (p > 0.05) interaction effect between water and nitrogen on percentage water saved.
Percentage of water saved was insignificantly (p < 0.05) higher under MC treatment than AWD treatment. Both water management treatments and N fertilizer, and their interactions had a significant (p < 0.05) effect on water productivity (
Parameter | Water mgt. (W) | Nitrogen management (N) | LSD (0.05) | |||||
---|---|---|---|---|---|---|---|---|
N0 | N1 | N2 | Mean | N | W | N × W | ||
Water use (cm3) | AWD | 48 | 49.3 | 50.5 | 49.3 | |||
MC | 23.1 | 26.4 | 32 | 27.2 | 0.95** | 0.96** | 1.66* | |
CS | 50.8 | 53.3 | 57.8 | 54 | ||||
Mean | 40.6 | 43 | 46.7 | |||||
Percentage water saved (%) | AWD | 20.4 | 15.5 | 20.8 | 18.3 | |||
MC | 27.9 | 26.5 | 28.3 | 27.8 | NS | 2.7** | NS | |
CS | - | - | - | - | ||||
Mean | 24.2 | 21 | 24.6 | |||||
Water productivity (g/cm3) | AWD | 0.51 | 0.82 | 1.05 | 0.79 | |||
MC | 0.65 | 1.06 | 1.09 | 0.96 | 0.3** | 0.3** | 0.05** | |
CS | 0.47 | 0.76 | 0.95 | 0.72 | ||||
Mean | 0.55 | 0.91 | 1.03 |
AWD: alternate wetting and drying soil condition; MC: moist soil condition between field capacity and permanent wilting point; CS: continuously submerged soil condition; N0, N1 and N2, are 0, 60 and 90 kg∙N∙ha−1 respectively. LSD: least significant difference; * means significant at 5%; ** means significant at 1%; NS means not significant at 5%.
The effect of various water management and N fertilizer rate on rice yields is shown in
Number of panicles/m2 was significantly (p < 0.05) influenced by water management and N fertilizer as well as their interactive effect (
Number of grains/panicle was significantly influenced by water management and N fertilizer (
Parameter | Water mgt. (W) | Nitrogen management (N) | LSD (0.05) | |||||
---|---|---|---|---|---|---|---|---|
N0 | N1 | N2 | Mean | N | W | N × W | ||
panicle/m2 | AWD | 275 | 369 | 401 | 349 | |||
MC | 232 | 324 | 400 | 319 | 12.3** | 10.2** | 363* | |
CS | 277 | 271 | 403 | 350 | ||||
Mean | 261 | 355 | 401 | |||||
Grains/panicle | AWD | 113 | 124 | 147 | 127 | |||
MC | 93 | 98 | 102 | 99 | 2.4** | 1.1** | 3.4* | |
CS | 113 | 124 | 148 | 128 | ||||
Mean | 106 | 115 | 133 | |||||
% filled grains | AWD | 89 | 91.2 | 92 | 90.9 | |||
MC | 90.3 | 86 | 91 | 92.4 | 1.1* | ns | ns | |
CS | 91.3 | 92 | 94 | 89.1 | ||||
Mean | 90.2 | 89.9 | 92.3 | |||||
1000 grain weight (g) | AWD | 26.9 | 27.1 | 26.4 | 26.8 | |||
MC | 27.1 | 26.6 | 27.1 | 26.9 | ns | ns | ns | |
CS | 27.2 | 27.5 | 27.4 | 27.4 | ||||
Mean | 27.1 | 27.1 | 27 |
AWD: alternate wetting and drying soil condition; MC: moist soil condition between field capacity and permanent wilting point; CS: continuously submerged soil condition; N0, N1 and N2, are 0, 60 and 90 kg∙N∙ha−1 respectively. LSD: least significant difference; * means significant at 5%; ** means significant at 1%; NS means not significant at 5%.
N rate on number of grains/panicle was significant (p < 0.05). Number of grains/panicle was not significant (p > 0.05) among AWD and SC treatment but, moist treated plants produced significantly (p < 0.05) lower number of grains/panicle. Based on N fertilizer, the number of grains/panicle varied in the order: N2 > N1 > N0. With interactions, N2 with SC and N0 with MC interaction produced significantly (p < 0.05) higher and lower number of grains/panicle respectively.
Percentage filled grains were significantly influenced N fertilizer treatments (p < 0.05) and ranged from 86.0% to 94.0% (
N fertilizer and Water management as well as their interaction did not significantly (p > 0.05) affect 1000 grain weight (
Water use was significantly (p < 0.05) influenced by both water management and N fertilizer application rate (
Percentage water saved was significantly (p < 0.05) influenced by N fertilizer and water management as well as their interactive effect (
Both water management treatments and N fertilizer application rates, and their interactions had a significant (p < 0.05) effect on water productivity (WP) of rice (
Generally, N2 fertilizer application rate required the higher cost of production followed by N1 fertilizer rate while N0 required the lower cost of production (
Parameter | Water mgt. (W) | Nitrogen management (N) | LSD (0.05) | |||||
---|---|---|---|---|---|---|---|---|
N0 | N1 | N2 | Mean | N | W | N × W | ||
Water use (mm) | AWD | 1031 | 1062 | 1132 | 1075 | |||
MC | 524 | 588 | 604 | 572 | 213** | 235** | 363* | |
CS | 1514 | 1552 | 1608 | 1558 | ||||
Mean | 1023 | 1067 | 1115 | |||||
Percentage water saved (%) | AWD | 33.83 | 31.84 | 27.34 | 31 | |||
MC | 66.37 | 62.26 | 61.23 | 65 | 3.4** | 2.1** | 5.0* | |
CS | - | - | - | - | ||||
Mean | 34.33 | 31.51 | 28.43 | |||||
Water productivity (Kg/cm3) | AWD | 0.28 | 0.44 | 0.57 | 0.43 | |||
MC | 0.42 | 0.58 | 0.73 | 0.58 | 0.02** | 0.02** | 0.04** | |
CS | 0.2 | 0.3 | 0.4 | 0.2 | ||||
Mean | 0.3 | 0.44 | 0.57 |
AWD: alternate wetting and drying soil condition; MC: moist soil condition between field capacity and permanent wilting point; CS: continuously submerged soil condition; N0, N1 and N2, are 0, 60 and 90 kg∙N∙ha−1 respectively. LSD: least significant difference; * means significant at 5%; ** means significant at 1%; NS means not significant at 5%.
production. Cultivation of rice with N2 under submerged and N0 under moist required the highest and lowest cost of production respectively.
Gross returns increased with increased N fertilizer application rate regardless of the water management regime (
Average net profit ranged from $688 to $3129.7 across the treatment combinations (
In
Parameter | Water mgt. (W) | Nitrogen management (N) | |||
---|---|---|---|---|---|
N0 | N1 | N2 | Mean | ||
Cost of production ($/ha) | AWD | 720.6 | 788.8 | 829.6 | 779.6 |
MC | 661.8 | 734.1 | 768.5 | 722.1 | |
CS | 779.1 | 845.7 | 888.4 | 828.8 | |
Mean | 720.5 | 789.5 | 828.8 | ||
Gross returns ($/ha) | AWD | 1812.1 | 2865.2 | 3959.2 | 2878.9 |
MC | 1350.6 | 2122.2 | 2739.5 | 2070.8 | |
CS | 1855.5 | 2843.4 | 3996.7 | 2898.5 | |
Mean | 1672.8 | 2610.1 | 3565.1 | ||
Net profit ($/ha) | AWD | 1091.7 | 2076.4 | 3129.7 | 2099.3 |
MC | 688 | 1388.1 | 1971 | 1349.3 | |
CS | 1076.4 | 1997.8 | 3108.3 | 2060.8 | |
Mean | 952.4 | 1820.8 | 2736.4 | ||
Benefit cost ratio | AWD | 1.52 | 2.63 | 3.77 | 0.43 |
MC | 1.04 | 1.89 | 2.56 | 0.58 | |
CS | 1.38 | 2.36 | 3.50 | 0.20 | |
Mean | 1.31 | 2.30 | 3.28 |
AWD: alternate wetting and drying soil condition; MC: moist soil condition between field capacity and permanent wilting point; CS: continuously submerged soil condition; N0, N1 and N2, are 0, 60 and 90 kg∙N/ha respectively. The exchange rate is GHȻ 4.46 = $1.00, GHȻ is Ghana Cedi, the local currency.
interaction effect was N2 with SC combination of N fertilizer and water combination. The lowest benefit cost ratio (1.04) was produced at N0 with moist interaction.
Plants fertilized with nitrogen had higher grain yield than unfertilized plants. This could also be attributed to efficient use of split application of nitrogen at transplanting and panicle initiation stage. This is in accordance with [
Yield parameters; panicles/m2, grains/panicles and test weight were higher in SC treatments though not significantly different from AWD treatments. Nonetheless lower yield parameters contributed in reduced yields as observed in the MC treatments. Grain yield showed no significant differences between SC and AWD treatments. Several authors have cited similar grain between SC and AWD indicating that AWD does not restrict water availability to rice plants. Since AWD plots were submerged at booting stage till ten days before harvest, yield penalties are not recorded. This is consistent with previous studies [
Interaction effect of N2 with AWD had similar yield as in submerged and N2 treatment combination. These observations might also be due to more N transported to the plant when plants were treated with higher doses of N. In all N0 under moist treatment combination gave the lowest grain yield due reduced moisture level at panicle initiation stage, similar to what was reported by [
Submerged water management received higher amount of water use than AWD and moist treatments due to the standing water layer maintained continuously on the plot from crop establishment till ten days to harvest. According to [
The highest water productivity was obtained under MC and AWD. AWD had higher water productivity than submerged treatment due to its lower water use. This finding was also reported by [
Interaction effect of N2 and submerged water management required higher water use due to higher evapotranspiration rate as a result of its higher leaf area index and evaporation [
The economic analysis from the study revealed that, it was highly economical to produce rice under AWD than the rest of the water management treatments. Although grain yields and gross returns from sales of rice were higher under submerged treatments than AWD water management, cost associated with water under submerged water management reduced net profit since general cost of production was same for all the water treatments. Moist treatment had the highest water productivity but the lowest gross returns from sales of rice due to reduced yields. The outcome agrees with the assertion by [
Results from the study revealed that rice yield differed significantly (p < 0.05) across the various N and water treatments. Nitrogen application rate of 90 kg/ha enhanced plant growth and development culminating to significant increases in grain yields. AWD resulted in similar yields to submerged water treatments and yields of rice were better with interaction effect of 90 kg N/ha and submerged water treatment. AWD required less water than continuous submergence for rice production and it was more cost-effective to produce rice under AWD than the rest of the water management methods. This indicates that continuous submergence is not an obligation in rice production and farmers could implement AWD and 90 kg N/ha to reduce water use, and increase water productivity while harvesting maximum yields with reduced cost of production.
Basing on the findings from the study, we recommend that further study on nutrient requirement of irrigated rice in Ghana is needed to investigate more nitrogen rates on different soil types and agro ecological zones. Also, future study should include soil moisture monitoring overtime and to quantify N leaching because of the high irrigation requirement of rice.
The authors are most grateful to the Office of Research, Innovation and Development (ORID), University of Ghana, for the sponsorship which has been of immense help in funding both the field work and laboratory analysis. We are also grateful to all those who contributed in diverse ways to make this study possible particularly the technical and support staff at the Soil and Irrigation Center (SIREC). This paper is a product of the research work done by the first author for his Master of Philosophy thesis in Crop Science (Agronomy) at the University of Ghana.
The authors declare no conflicts of interest regarding the publication of this paper.
Yakubu, A., Ofori, J., Amoatey, C. and Kadyampakeni, D.M. (2019) Agronomic, Water Productivity and Economic Analysis of Irrigated Rice under Different Nitrogen and Water Management Methods. Agricultural Sciences, 10, 92-109. https://doi.org/10.4236/as.2019.101008