Kodjari Phosphate Rock for Rain-Fed Lowland Rice Production in the Sudan Savanna, Burkina Faso

Trop. Agr. Develop. 64（2）： 97 － 106，2020

Kodjari Phosphate Rock for Rain-fed Lowland Rice Production in the Sudan Savanna, Burkina Faso

Satoshi NAKAMURA1, *, Simpore SAIDOU2, Albert BARRO2, Dambinga JONAS 2, Monrawee FUKUDA1, Takashi KANDA1,3, and Fujio NAGUMO1

1 Japan International Research Center for Agricultural Sciences (JIRCAS) 1-1 Owashi, Tsukuba Ibaraki 305-8686, Japan 2 l’Institut de l’Environnement et de Recherches Agricoles (INERA) INERA/Saria, BP10 Koudougou, Burkina Faso 3 Institute for Agro-Environmental Sciences, NARO (NIAES), 3-1-3 Kannondai, Tsukuba, Ibaraki 305-8604, Japan

Abstract Local phosphate rock use in sub-Saharan Africa (SSA) has immense potential to enhance African crop productivity. The effects of Kodjari phosphate rock direct application (PRDA) were studied in a rain-fed lowland rice (Oriza Sativa L.) fields with two levels of N applications, under different duration of submergence affected by seasonal flooding in the Sudan Savana of Burkina Faso. During the first year, PRDA with 90 kg N ha-1 did not affect rice yields whereas PRDA with 30 kg N ha-1 resulted in 91% yield obtained by using triple super phosphate (TSP). However, in the following season, successive PRDA indicated comparable effects as those of TSP application with both 30 and 90 kg N ha-1. Although TSP application indicated higher residual effects than that of PRDA, our investigation identified capital P replenishment by PRDA in the rain-fed lowland-rice cultivation area in the Sudan Savanna. Longer submergence duration resulted in higher PRDA effects. In conclusion, the high potential of PRDA on lowland rice was demonstrated in the Sudan Savanna zone. Considering previous studies, PRDA can be regarded as an effective technical option for lowland rice cultivation in the SSA. Although the effects of initial PRDA might have been depressed under water-limited conditions, it can contribute to improvement of soil P availability with replenishment of capital P for enhancing lowland rice production in SSA. Key words: Burkina Faso, Capital P replenishment, Low-grade phosphate rock, Lowland rice, Relative agronomic effectiveness

mainly focusing on upland crops. Thus, the effects of Introduction PRDA on rain-fed lowland rice growth in this region has Utilization of local African phosphate rock (PR) not been fully evaluated. can be considered a key factor in the solution of Authors have focused on PRDA in lowland rice hunger and poverty in Africa through improvement of cultivation because of reports that shows positive ef- crop productivity (Appleton, 2002). Large amounts of fectiveness of PRDA with this crop (Nakamura et al., phosphate deposits exist in sub-Saharan Africa (Appleton 2013a). Owing to population growth, the demand for 2002; Nakamura et al., 2013a), they have not been fully rice in SSA has been increasing (Somado et al., 2008). utilized because of limited solubility and/or impurity Rice production in SSA remains inadequate because content (FAO, 2004). Previous studies have attempted of its low productivity due to the limited application of to utilize these low-grade PRs with various crops agrochemicals and fertilizers. (Ankomah et al., 1995, Bationo et al., 1997; Adesanwo High demand for rice production has been increas- et al., 2012; Hamza and Akinrinde, 2016), and have ing in Burkina Faso. The domestic supply of paddy rice indicated that the effectiveness of PR direct application reached 650 kt in 2013, but total amounts of imported (PRDA) shows substantial variation, due to PR solubility, rice have also increased to 724 kt in Burkina Faso, sug- soil properties, and the types of crops (Rajan et al., gesting the imported rice has supplied a large percent- 1996). In 1980’s, the National Institute for Environment age of the rice demand in Burkina Faso. This situation and Agricultural Research (INERA) has investigated the has been caused by limited increases in unit crop yields, effects of PRDA on various crops, such as maize, cotton, which were 2.1 t ha-1 in 1989 and 2.2 t ha-1 in 2013. Crop sorghum, and rice, in Burkina Faso (Hien et al., 1992; productivity in this country is believed to be limited by Bonzi et al., 2000). However, these studies have been low rate of fertilizer application (Morris et al., 2007), especially phosphorus (P) fertilizer, although nitrogen Communicated by Y. Nitta Received Nov. 12, 2019 (N) has been more liberally applied (Van der Velde et Accepted Mar. 18, 2020 al., 2014). It is known that P deﬁciency is a constraint on * Corresponding author crop production in the SSA (Sanchez, 2002; Nziguheba [email protected] ORCiD: 0000-0002-0952-5618 et al., 2016). 98 Trop. Agr. Develop. 64（2）2020

Water conditions of rain-fed lowland rice fields will two levels of N application in the Sudan Savanna. affect PR solubilization and to the effect of PRDA on Materials and Methods rain-fed lowland rice yield. Rajan et al. (1996) pointed that increasing of soil water content with irrigation and/ Study site or rainfall will increase dissolution of PR. In the incuba- This study was conducted in seven communities tion study, PR dissolution was increased with increase located near the l’Institut de l’Environnement et de of soil water content up to 80% of field capacity (Weil et Recherches Agricoles (INERA), Saria station (2°09’W, al., 1994). And Hammond et al. (1986) reported linear 12°16’N; 300m asl.). Soils distributed in this region have relationship between the effect of PRDA and annual been classified as Plinthic Lixisols and/or Pisoplinthic rainfall under the range from 500 to 1300 mm. However, Plinthosols, according to the soil atlas of Africa (Jones et there was little information about impacts of soil and/ al., 2013). Seven communities were randomly selected, or water condition in the effect of PRDA on lowland rice and one site was selected per community. Rain-fed low- cultivation in the Sudan Savanna zone. land rice cultivation has been conducted in floodplains The authors have investigated the effects of PRDA and inland valleys, usually without fertilizer application. on lowland rice in the Guinea Savanna zone and Equa- The climate of this area was characterized by mono- torial Forest zone, where are typical zones of lowland modal rainfall from May to October with a mean of 800 rice cultivation in West Africa (Nakamura et al., 2013b; mm yr-1, and annual mean temperature of 28 °C (28.5 °C Nakamura et al., 2016), and mentioned water shortage for rainy season and 27.8 °C for dry season), recorded adversely affect the effect of PRDA on rain-fed lowland at INERA-Saria station. rice cultivation. And these studies showed importance of residual effect of PRDA. The PRDA indicated high Phosphate rock used in this experiment residual effect in lowland rice cultivation in both agro- There are phosphate deposits at Kodjari in Burkina ecological zones (Nakamura et al., 2016). However, the Faso, and at Tapoa in Niger (Trompette, 1989). The effects of PRDA and its residual effects have not been Kodjari deposit was estimated to contain 60 million Mg fully examined for lowland rice cultivation in the Sudan of PR. The Kodjari PR contains 25% P2O5 on average Savanna zone, although a few studies evaluated the ef- (FAO, 2004), its solubility was classified as having low fects of PRDA on rice since the 1980s (Hien et al., 1992). reactivity (Bationo and Mokwunye, 1991) by Diamond’s Further, effects of PRDA would be affected by soil classification (Diamond, 1979). nitrogen (N) fertility. As suggested by Chien (1979), The well-powdered PR was used in this study. N application can enhance PR use efficiency through Chemical composition and solubility of the PR used stimulation of plant growth. Although most of previous were analyzed according to FAMIC (2013), contained -1 -1 studies have applied enough N fertilizer to show P 117 g P kg PR (268 g P2O5 kg PR ) (Table 1). Phosphate source effect, the practices of farmers in lowland rice content in the PR was agreed with a reported value (250 -1 cultivation of SSA have highly limited N application. It g P2O5 kg PR ; FAO 2004). Citric acid solubility of this may be possible mislead understandings of PRDA effect PR was 21.4%, whereas it contained little water-soluble P. on lowland rice cultivation in SSA. Calcium (Ca) in PR could have an additional liming ef- The objective of this study was therefore to evalu- fect (Sikora, 2002), as it contained 236 g Ca kg-1 PR and ate PRDA and residual effects on rain-fed lowland rice 29.9% of total Ca was soluble in 2% citric acid solution. cultivation under various water conditions, and under

Table 1. Chemical composition and solubility of phosphate rock produced at Kodjari in Burkina Faso. Total Citric acid soluble† Water soluble† Citric acid solubility†† Water solubility†† g kg PR-1 % Phosphorus (P) 117 25.1 0.07 21.4 0.27 Calcium (Ca) 236 70.5 0.15 29.9 0.22 Potassium (K) 3.62 1.02 0.03 28.2 2.76 Magnesium (Mg) 0.80 0.16 trace 20.5 - Sulfur (S) 7.71 trace trace - - † Soluble elements in 20 g L-1 of citric acid solution and distilled water for citric acid and water solubility, respectively. †† Percentage of each soluble fraction relative to the total content of elements in phosphate rock. Nakamura et al.: Effect of Kodjari phosphate rock application on lowland rice 99

Plot design and yield survey P source application. Investigations were conducted from 2013 to 2015. Fertilizers of P and K were applied as a basal ap- During the first season, the effects of PRDA on lowland plication, whereas N fertilizer was divided into basal rice cultivation were evaluated in seven sites represent- and top-dressing at five weeks after seed sowing. In the ing seven replications. Our study conducted as farmers second year, plots for evaluating residual effects were practice; rainfed cultivation depending on flooded water, not received P application, whereas successive applica- with no puddling and levelling. Each plot had an area of tion plots received the same amounts of P application as 25 m2, with a surrounding bund of approximately 30 cm the initial application. In the third year, P was not applied in height to collect water and prevent overflowing of the and N and K were also applied as the first year. applied nutrients. The residual effects were determined Rice seeds were sowed by direct sowing at begin- through dual partitioning of P-source amended plots ning of July with spacing of 20 × 20 cm, and harvested into two sub-plots of residual effect and successive ap- middle of October, although it was varied due to differ- plications. Furthermore, two years of residual effects ence of precipitation pattern. Hand-weeding was done were subsequently evaluated in 2015 by proving no P twice during the cultivation period by farmers. Panicle application to the plots. The outlines of experiments 1 to number, kernel panicle-1, and 1000-kernel weight were 3 were shown as Fig. 1. measured. Rice grain yields were evaluated by using Treatments were shown in Table 2. The first year yield components, whereas the weight of harvested rice treatments were “Zero”: no application (0N-0P-0K kg grains were also identified for yield evaluation. ha-1) , “PR”: PRDA without NK application (0N-60P-0K), To elucidate the effects of flooding and/or sub- “NK”: NK application without P application (90N-0P- mergence duration, water depths in the studied fields 50K), “PR90NK”: PRDA with NK application (90N-60P- were monitored twice per week for three years at each 50K), “TP90NK”: TSP application with NK application site. Duration of submergence was estimated as a sub- (90N-60P-50K), “30NK”: one third rate N application mergence will be continued for three days if monitored with K (30N-0P-50K), “PR30NK”: PRDA with one third depth was over 50 cm, and one day if monitored depth N and K (30N-60P-50K), and “TP30NK”: TSP application with one third N and K (30N-60P-50K). Nitrogen Table 2. Summary of experimental treatments.

(N) was applied as ammonium sulfate ((NH4)2SO4), P N K ID P source and muriate potash (KCl) was used as a potassium (K) kg ha-1 source. Triple super phosphate (TSP) was applied as Zero 0 0 0 water-soluble P fertilizer for comparison with PR. The PR PR† 60 0 0 -1 90NK 0 90 50 P sources were applied at the rate of 135 kg P2O5 ha (60 kg P ha-1). The K fertilizer was consistently applied PR90NK PR 60 90 50 †† -1 -1 TP90NK TSP 60 90 50 at the same rate of 60 kg K2O ha (50 kg K ha ) to all 30NK 0 30 50 experimental plots, except Zero and PR. Two levels of PR30NK PR 60 30 50 N fertilizer were applied, the recommended level (i.e., TP30NK TSP 60 30 50 90 kg N ha-1) and limitation level (i.e., 30 kg N ha-1), to †PR: Phosphate rock, ††TSP: Triple super phosphate evaluate the effects of N fertilizer on the effectiveness of N and K was applied as (NH4)2SO4 and KCl, respectively

Experiment 1 Experiment 2 Experiment 3

P source Non P P source Non P Non P application application

Residual effect 2-year sequential 2-year residual 1-year residual of 1st application application of P effect effect sources of P application of previous in 1st year application

Fig.Figur 1. Outlinee 3. O ofutlin experiments.e of conducte The P sourcesd experiments are Burkina. Th Fasoe P phosphatesources rockare (PR)Burkin or triplea Fas supero Phosphate phosphate (TSP). All plots received N and K fertilizer for each site rock (BPR) or Triple Super Phosphate (TSP). All plots received N and K fertilizer for each study site. 100 Trop. Agr. Develop. 64（2）2020 was over 15 cm, based on field observation. Additionally, Ca, K, magnesium (Mg), and sulfur Chemical analysis procedure for soil samples and (S) concentrations in each extract were determined with phosphate rock ICP-AES by using an ICPE-9000 (Shimadzu, Japan) to Five surface soil samples of 0-20 cm depths were assess the solubility of expected subsidiary elements in collected from each plot and composited as one sample, the studied PR. at pre- and post- cultivation for each crop. Soil samples were analyzed after air-drying and passing through Statistical analyses and indices for evaluation of a 2-mm sieve. Soil pH and EC were determined by the effects of PRDA the glass electrode method by using a LAQUA F-72 Multiple comparisons were conducted by Tukey’s (HORIBA, Japan) and EC meter ES-51 (HORIBA, Japan) HSD method by using Kyplot version 4.0 (Kyence, after extraction in a 1: 2.5 soil: water ratio. Total carbon Japan) to identify significant differences between vari- (C) and total N were determined by the dry combus- ous treatments. The significance of differences between tion method by using an NC analyzer NC 220F (Sumika the successive application plot and residual effect was Chemical Analysis Service, Japan). Available P was identified with student’s t-test. extracted (Bray and Kurtz 1945) and the concentration Effects of PRDA were evaluated by relative yield was determined by using the ascorbic acid-molybdenum (RY) and relative agronomic effectiveness (RAE). blue method. Exchangeable bases were extracted by / (1) using a 1.0 M ammonium acetate solution (pH 7.0). E － / － (2) Then, the concentrations of cations were determined by t t -1 inductively coupled plasma atomic emission spectropho- where YPR is yield with 60 kg P ha as PR application, -1 tometry (ICP-AES) by using an ICPE-9000 (Shimadzu, YTSP is yield with 60 kg P ha as TSP application, and

Japan). The P fixation capacity was determined by using YCont is yield with no P application under the same levels the ammonium phosphate method (ECAMS, 1997): 50 of NK application. mL of 2.5% (NH4)2HPO4 solution (pH 7.0) was added to For calculation of RY and RAE, PR and TSP were the 25 g of soil sample and allowed to stand for 24 h at applied at same rate as P. The index value designations room temperature. Absorbed P was calculated as the were RY1 and RAE1 with 90 kg N ha-1 and RY2 and difference in P concentration in the solution before and RAE2 with 30 kg N ha-1. after the soil addition. Results and Discussion The solubility of PR was determined as water solubility and 20 g L-1 citric acid solubility against total Initial soil properties and water conditions of content, according to FAMIC (2013). For the determina- study sites tion of total P, 5 g of grounded PR was digested for 30 The effects of PRDA are affected by site-specific min in 30 mL of concentrated hydrochloric acid (HCl) soil properties, such as soil pH, soil organic matter and 10 mL of concentrated nitric acid (HNO3), follow- content, and soil P fixation capacity (Smalberger et al., ing ammonium vanado-molybdate absorptiometric 2006). Initial soil pH ranged from 5.07 to 5.96 with an determination by using an ultraviolet - visible light average of 5.4 (Table 3). The content of Bray-I P was < spectrophotometer, UV-1800 (Shimadzu, Japan). Citric 4 mg kg-1 and it indicates low P availability (Mallarino et acid soluble P was extracted in 20 g L-1 citric acid. A 1-g al., 2013), and Bray-I P was positively related to EC. The sample was determined on an analytical scale and placed P fixation rate ranged from approximately 0.55 to 2.11 g -1 in a 250 mL volumetric flask. To this, 150 mL of citric P kg , corresponding to 4.7-18.0 % of added P2O5 fixed acid solution (20 g L-1) was added and heated under ap- by the soil. proximately 30 ºC, and shaken for 1 h. The solution was Fig. 2 indicates that submergence duration was cor- allowed to cool and the volume was replenished with related with soil total C content (r = 0.87, p < 0.05) and distilled water. Next, it was filtered through paper filter soil P fixation rate (r = 0.78, p < 0.05). The correlation No. 3 (Advantec, Japan) to collect the sample solution. between total C content and P fixation rate was high (r Water-soluble P was extracted at a 1:100 solid: liquid = 0.975, p <0.001). The organic debris is collected by rate, shook for 30 min, and filtered through paper filter surface runoff in the lowlands during submergence. No. 3. The P content in both extracts was determined by Thus, the accumulated soil organic matter can affect using the vanado-molybdate yellow method, in the same soil P fixation rates at these sites. It is also explained by manner as that of total P determination. soil reduction reflecting submergence duration, longer Nakamura et al.: Effect of Kodjari phosphate rock application on lowland rice 101

Table 3. Water conditions and soil initial chemical properties of study sites. Duration of Exchangeable cation pH EC Bray I P T-N T-C P ﬁxation submergence Ca Mg K Na -1 -1 -1 -1 -1 days per season H2O mS m mg P kg cmolc kg g kg g P kg Nassoulou 28.7 ± 1.5 5.96 3.09 0.87 4.10 1.46 0.14 0.10 0.54 7.65 1.55 Sissené 45.3 ± 11.9 5.45 5.52 1.55 3.37 1.38 0.19 0.11 0.64 9.37 1.82 Poa-sicobsé 39.7 ± 6.4 5.48 5.52 2.19 1.91 0.62 0.08 0.07 0.49 6.11 0.86 Villy 52.7 ± 2.5 5.16 7.57 3.74 3.05 1.06 0.41 0.14 1.01 12.13 2.11 Siguinvoussé 26.0 ± 1.0 5.07 4.37 1.38 0.72 0.23 0.09 0.06 0.39 4.69 0.83 Ramongo 23.0 ± 2.6 5.30 3.03 1.71 0.48 0.16 0.05 0.06 0.22 2.84 0.55 Nandiala 84.3 ± 25.1 5.40 4.95 1.83 3.76 1.62 0.32 0.09 0.80 11.35 1.97 Chemical properties indicated in this table are properties of soil samples taken before land preparation in 2013. Duration of submergence is indicated as mean days per season over three years (2013-2015).

7.0 y = 6.56 ln(x) - 16.29 7.0 14 r = 0.869* ) 6.0 -1

6.0 12 1 a - 1 5.0 - kg kg g 5 5.0 10 4.0 O

2 b P bc bc g 4.0 8 3.0

y = 2.46 ln(x) - 5.86 content bc r = 0.783* c rate 3.0 6 2.0 c c carbon

2.0 4 ha (Mg yield grain Rice 1.0 fixation otal

P 系列P fixation1 T 1.0 2 0.0 系列Total2 carbon content 0.0 0 15 35 55 75 95 Mean duration of submergence (days) Fig. 3.Figure Year 5. 1 Effecteffect of of phosphatephosphate rock rock direct direct application application on on lowlandlowland rice grainrice yieldgrain in Burkinayield in Faso. Burkina Faso, result in Fig. 2. Relationships between mean duration of Error bars indicate standard error (n = 7) Different letters indicate significant differencesexperiment (p < 0.05) by1. Tukey’s HSD multiple comparison. RY and RAE are submergence and soil P fixation rate and total C abbreviations Error ofbars relative indicate yield and relative standard agronomic error effectiveness, (n = respectively. 7). Different content among seven study sites. Suffixed numbers indicate two of N application rate used for calculation, 90 kg N haletters-1 for “1” ,indicate and 30 kg N significant ha-1 for “2”, respectively. differences (p < 0.05) according Asterisks denote significant correlations (p < 0.05). to Tukey’s HSD multiple comparison. submergence can cause increase of P absorption due to cultivation is effective in Burkina Faso, and the effect on increase of ferrous ion. lowland rice was affected by soil N availability. In the N- limited condition, indices of PRDA effects were higher Effects of current PRDA on lowland rice yield than in the N-rich condition. This was attributed to a Grain yield with PR90NK was 3.0 Mg ha-1 compared lower P requirement by rice plants because of limited with 5.0 Mg ha-1 for TP90NK and 2.2 Mg ha-1 with PR plant growth under N shortage. This is also supported (Fig. 3). The values of RY1 and RAE1 were 61.3 and 29.8, by evaluated yield components (Table 4). In the N-rich respectively. condition, there were no significant differences in num- In the N-limited condition, RY and RAE of PRDA bers of grains and 1,000-kernel weight, but the signifi- had a greater effect on lowland rice production than did cant difference was identified for the number of panicles. the treatment with recommended N application, RY2 Kernel panicle-1 can be affected by soil P content. That and RAE2 were 91.1 and 74.0, respectively. The PR30NK is, P deficiency leads tillering limitation (Yoshida and produced a 2.3 Mg ha-1 rice yield, which was 24% lower Hayakawa, 1970). Conversely, in the N-limited condi- than that of the PR90NK treatment, reflecting the ef- tion, only 1,000-kernel weight was significantly different fects of N limitation on rice yield. The TP30NK showed among 30NK, PR30NK, and TP30NK. a greater yield depression compared with that of PR The effects of PRDA on lowland rice in Burkina application. Rice yield with the TP30NK treatment was Faso were relatively low compared with previous studies 2.6 Mg ha-1, which was 49% lower than that of TP90NK. in rice fields located of the Guinea Savanna and Equato- These results suggested that PRDA for lowland rice rial Forest zones in Ghana (Nakamura et al., 2013b). In 102 Trop. Agr. Develop. 64（2）2020

Table 4. Yield components observed in Experiment 1. 1000-kernel wt. Grain yield Treatments Panicles m-2 Kernel panicle-1 g Mg ha-1 Zero 99 d 59.1 a 24.1 bc 1.40 c PR 97 cd 57.0 a 24.3 bc 1.28 c 90NK 186 bc 60.0 a 24.2 bc 2.23 bc PR90NK 211 b 69.3 a 24.1 bc 3.05 b TP90NK 265 a 82.7 a 24.8 b 4.97 a 30NK 151 bc 52.5 a 23.3 c 1.67 c PR30NK 174 bc 59.3 a 24.4 bc 2.32 bc TP30NK 185 bc 59.7 a 25.9 a 2.55 bc Different alphabets in each column indicate signiﬁcant difference (p < 0.05) according to Tukey’s HSD multiple comparison (n = 7).

Ghanaian rice cultivation, RAEs indicated the recom- 7.0 mended N application was 84% in the Guinea Savanna Suc RY1 = 107.3, RAE1 =120.4 Res RY1 = 59.9, RAE1 =1.2 zone and 143% in the Equatorial Forest zone. Lower 6.0 *** A

) Suc RY2 = 92.8 Successive a ab RAE1 compared with results in Ghana might have been -1 a 5.0 RAE2 = 82.1 h Residual Res RY2 = 102.0 caused by less precipitation and soil physico-chemical (t RAE2 = 107.3 4.0 properties of the Sudan Savanna zone, particularly soil b b yield B water content. It has been previously elucidated that 3.0 bB BC BC PR solubilization is enhanced with increased soil water grain bc 2.0 C bcBC content (Rajan et al., 1996). However, our observation Rice cC explained that the effects of PRDA was also variable 1.0 with soil N fertility. Although N fertilizers have been 0.0 sufficiently applied in these experimental areas, organic matter content and its decomposition rate may affect the effects of PRDA on lowland rice cultivation. The effects of regional differences among various agro-ecological Fig. 4. Residual effects of phosphate rock direct application zones on the effects of PRDA on lowland rice require on lowland rice grain yield in Burkina Faso, results of further investigated. experiment 2. Error bars indicate standard error (n = 7). Different letters indicate significant differences (p < 0.05) by Tukey’s HSD Residual effects of PRDA on lowland rice in multiple comparison. Small letters and capital letters are Burkina Faso significance among the successive plots and the residual plots, respectively. Asterisks above the bars denote With the recommended N applied, successive appli- significant difference between successive (Suc) and cation of PR (PRNK) resulted in comparable rice yields residual (Res) plots by Student’s t test. ***: p < 0.001 (4.7 t ha-1) with those of TPNK (4.3 t ha-1) in Experiment 2. Although effects of PR application were not obvious residual effect appearance mechanism in PR and TSP. in Experiment 1, successive application of PR appeared A previous study conducted in Ghana (Nakamura et to improve lowland rice yield (Fig. 4), possibly because al., 2016) suggested that the residual effects of PRDA of accumulated phosphate in the soil from previous PR were affected by soil water condition. In locations where application. However, in residual effects plot, PRDA have greater water percolation, water-soluble phosphate showed significant decreases in rice grain yield com- fertilizer had less residual effects than did PRDA due to pared with successive plots, whereas TSP maintained high nutrient loss by leaching. Our study was conducted comparable rice yield with its successive application in rain-fed cultivation. It is possible that the effects of (Fig. 4). This explained that TSP has greater residual water migration and/or percolation at our study sites effects than PR on lowland rice cultivation in Burkina were weaker in comparison with water management Faso. These results are in agreement with those of practiced in inland valleys of the Equatorial Forest zone. Rajan et al. (1996) who reported that the residual effects Alternatively, the difference in the yield response for PR of water-soluble P fertilizer were higher than those of application between the experiments 1 and 2 indicated PRDA in the short term owing to differences in the that the initial PR application replenished soil P fertil- Nakamura et al.: Effect of Kodjari phosphate rock application on lowland rice 103

ity. That is, residual effects did not supply a sufficient application is less expensive for PRDA than TSP based P amount for rice growth, but it is possible that the on market prices. Local PR can be purchased at 25% of initial PR application supplied P to partially fill the soil P- TSP price. fixation capacity, and consequently the next application In the 1990s, the concept of “capital P” was advo- of PR produced a comparable yield as that by using TSP. cated, which is the soil P stock that serves as a major Residual effects were identified in the experiment 3 sink for added P and gradually releases plant available and all experimental plots received only N and K fertil- P for up to 10 years (Sanchez and Palm, 1996; Buresh izers. Although PR application indicated lower residual et al., 1997). The results suggested that PRDA can effects after two years (128% and 121% compared to the contribute to the replenishment of soil capital P, even NK and 30NK for PR90NK and PR30NK, respectively), though PRDA did not show immediate positive effects TSP showed strong residual effects in two years after in crop production due to low solubility of PR. And PRs the initial application (Table 5). The phosphorus-use with very low reactivity may need solubility improved efficiency (PUE) was calculated following Nakamura through chemical-, and/or thermo-processing, such as et al. (2016). The PRDA showed high PUE in the two- partial acidulation (Rajan and Marwaha, 1993) and cal- year successive application and the following season in cination with sodium carbonate (Nakamura et al., 2015). N-rich conditions, whereas TSP application showed high Capital P replenishment can contribute to the increased PUE with a one-year application and two-year residual crop production in subsequent cropping season because effects in both N-rich and N-limited conditions. This sug- of the increase in available P and a decrease in P fixation gested that PRDA should be applied twice every three rate. years in N-rich conditions and once per three years in N-limited conditions for enhancing PUE. On the other Relationship between soil properties and PRDA side, TSP can be applied once per three years. Although effects on lowland rice cultivation PRNK applied twice per three years yielded 14% lesser As discussed above, PRDA effects are influenced by than TPNK applied once per three years, this rate of a wide range of soil conditions (Smalberger et al., 2006).

Table 5. Two-year residual effects of phosphate rock direct application and phosphorus use efﬁciencies in several patterns of application, results from experiment 1, 2, 3. Grain yield ratio Averaged grain yield Averaged grain yield Total P P application against and PUE in 2 years and PUE in 3 years application in 3 years†† control††† (13/14) (13/14/15) in 3 years 2013 2014 2015 yield PUE* yield PUE* 13/14/15 kg P ha-1 % Mg ha-1 kg kg-1 year-1 Mg ha-1 kg kg-1 year-1 Zero 0/0/0 0 100 100 100 1.24 1.26 PR Suc† +/+/0 120 91 160 119 1.50 4.6 1.52 6.7 Res† +/0/0 60 91 137 104 1.38 4.8 1.37 5.7

90NK 0/0/0 0 100 100 100 2.51 2.32 PR90NK Suc +/+/0 120 137 167 168 3.85 22.7 3.65 33.9 Res +/0/0 60 137 101 128 2.93 14.2 2.79 23.6 TP90NK Suc +/+/0 120 223 155 168 4.66 36.4 4.19 47.4 Res +/0/0 60 223 168 160 4.84 78.8 4.26 98.8

30NK 0/0/0 0 100 100 100 1.73 1.71 PR30NK Suc +/+/0 120 139 156 136 2.54 14.0 2.46 19.0 Res +/0/0 60 139 141 121 2.41 23.4 2.29 29.3 TP30NK Suc +/+/0 120 152 168 141 2.77 17.6 2.63 23.6 Res +/0/0 60 152 138 149 2.50 26.4 2.50 40.3 †Suc and Res are the abbreviation for ‘successive application plot’ and ‘residual effect plot,’ respectively. ††Presence or absence of P source application indicated ‘+’ as presence, and ‘0’ as absence. †††Grain yield ratio compared to yield in control (NK) plot. *PUE; Phosphorus use efﬁciency is calculated as follows, PUE (kg kg-1 year-1) = (Yp – Ycont)/ Pfert. where Yp is the 2nd- or 3rd-year total yield in the P-fertilizer application plot, Ycont is the 2nd- or 3rd-year total yield in the control plot, and Pfert is total P application in 2nd- or 3rd- years. 104 Trop. Agr. Develop. 64（2）2020

The RY is the indicator of the effects of PRDA and it was Chien et al., (1990) reported the difficulty in com- significantly correlated with soil EC, Bray I-P content, paring the relative effectiveness of PRDA because of total C and N contents, and duration of submergence variability in their mineralogical composition. In general, (Fig. 5). Soil EC values were affected by the content of effectiveness of fertilizer application can be elucidated inorganic and/or organic compounds, such as P, N, and with RYs using relative yield versus yield with standard organic matter. As previously discussed, soil properties fertilizer, although previous studies about PRDA have in this region are dominated by water conditions. Our recently employed RAEs. The RAE is one of the most study revealed that PRDA should have a high effect in widely used indicators that reflect the comparative ef- a location where has higher P, N, and organic matter fectiveness of PR applications. However, this indicator content, owing to soil water conditions. However, actual appeared to suffer from problems. The RAE shows contributions of each factor on the effects of PRDA have dramatic values in cases where yield would be similar not been fully elucidated because of the limited number between the control and TSP. For example, if YCont, YPR, of investigated sites in our study. Larger numbers of and YTSP were 2.00 t, 2.10 t, and 2.01 t, respectively, RAE sites will be required to identify the contribution of these would be 1000%. Furthermore, RAE can produce a nega- factors. Furthermore, the adequacy of the indices for the tive value if either YPR or YTSP is lower than YCont. These effects of PRDA (RY and RAE) should be examined. In impractical values are likely to be obtained in a farmer’s our investigation, RAE values did not show any signifi- field where is not fully controlled or managed, especially cant correlations with soil properties, possibly because in the SSA. of erratic RAE values. Consequently, a relative effectiveness (RE) index

1.8 1.8 N90 y = 0.766ln(x) - 0.179 y = 0.426ln(x) + 0.763 1.6 N30 1.6

yield r = 0.922** r = 0.693 yield 1.4 1.4 grain 1.2 grain 1.2 rice 1.0 rice 1.0 in in s s 0.8

Y 0.8 Y R R 0.6 0.6 0.4 0.4 2.0 4.0 6.0 8.0 0.0 1.0 2.0 3.0 4.0 Soil EC mS m-1 Bray I P mg P kg-1 1.8 y = 0.462ln(x) + 2.355 1.8 y = 0.484ln(x) - 0.774 r = 0.842* r = 0.802* 1.6 1.6 yield yield 1.4 1.4 grain 1.2 grain 1.2 rice 1.0 rice 1.0 in in s 0.8 s 0.8 Y Y R R 0.6 0.6 0.4 0.4 0.00 0.03 0.06 0.09 0.12 15 35 55 75 95 Total N (%) Mean duration of submergence (days) Fig. 5. Influence of field conditions for phosphate rock direct application effect on lowland rice cultivation in the Sudan Savanna zone. The RYs of markers indicate mean value of 3 years data at each site Approximation formulas shown in figures are computed for N-limited condition. Asterisks indicate significant correlations ** (p < 0.01), and * (p < 0.05) Nakamura et al.: Effect of Kodjari phosphate rock application on lowland rice 105 was suggested by Chien (1990). The RE index is calcu- Appleton, J. D. 2002. Local phosphate resources for sustainable lated as the relative ratio of the regression coefficients development in sub-Saharan Africa: British Geological Survey Report, CR/02/121/N (Keyworth, Nottinghum) pp.145. from PR and TSP, of equations which is approximated by Barrow, N. J. 1985. Comparing the effectiveness of fertilizers. the relationship between P source application rate and Fertil. Res. 8: 85-90. yield increase, as used by Leon et al. (1986) and Bationo Bationo, A., E. Ayuk, D. Ballo, and M. Kone 1997. Agronomic and economic evaluation of Tilemsi phosphate rock in different et al. (1990). The RE index is considered the best index agroecological zones of Mali. Nutr. Cycl. Agroecosyst. 48: of effectiveness for PR compared with TSP, and avoids 179-189. the error of evaluation caused by differences in P appli- Bationo, A., S. H. Chien, J. Henao, C. B. Christianson, and A. U. Mokwunye 1990. Agronomic evaluation of two unacidulated cation rate (Barrow, 1985). However, it requires several and partially acidulated phosphate rocks indigenous to Niger. levels of P source applications for both of PR and TSP Soil. Sci. Soc. Am. J. 54: 1772-1777. to calculate the regression coefficient. It is difficult to Bationo, A. and A. U. Mokwunye 1991. Alleviating soil fertility constraints to increased crop production in West Africa: The conduct in a multi-location experiment, especially in an experience in the Sahel. Fertil. Res. 29: 95-115. area-limited site, such as our study. Bonzi, M., F. Lompo, N. Ouandaogo, and P. M. Sédogo 2000. Promoting uses of indigenous phosphate rock for soil fertility Conclusion recapitalization in the Sahel: State of the knowledge on the review of the rock phosphates of Burkina Faso. In: Innovations Effects of Kodjari PRDA were evaluated for lowland as Key to the Green Revolution in Africa (Bationo A, et al. rice cultivation in the Sudan Savanna zone, Burkina eds.) Springer (Berlin) p. 381-390. Bray, R. M. and L. T. Kutz 1945. Determination of total, organic Faso. Our study clarified that PRDA can improve rice and available forms of phosphorus in soils. Soil Sci. 59: 39-45. grain production with two-year consecutive application, Buresh, R. J., P. C. Smithson, and D. T. Heliums 1997. Building soil but the initial application did not yield satisfactory phosphorus capital in Africa. In: Replenishing soil fertility in Africa. (Buresh et al. eds.) SSSA Special publication 51, Soil results compared with TSP application. This suggests Sci. Soc. Am., pp 111-150. that PRDA can contribute to enhance soil capital P in Chien, S. H. 1979. Dissolution of phosphate rock in acid soils as the first application, and results in comparable rice yield influenced by nitrogen and potassium fertilizers. Soil Sci. 127: 371-376. to TSP with the accumulation of P in the second year Chien, S. H., P. W. G. Sale, and D. K. Friesen 1990. A discussion of cultivation. Furthermore, we found that the effects of the methods for comparing the relative effectiveness of of PRDA on lowland rice yield are higher in N-limited phosphate fertilizers varying in solubility. Field Res. 24: 149- 157. conditions, and higher in soil conditions of longer dura- Diamond, R. B. 1979. Views on marketing of phosphate rock for tion of submergence. To evaluate site-specific PRDA direct application. Special Publication, International Fertilizer effects accurately, more practical indices are required, Development Center (Muscle Shoals) pp. 448-463. Editorial Committee of the Analytical Method of Soil Environment especially for the examination in the farmer’s fields (ECAMS) 1997. The Analytical Method of Soil Environment. where have land limitations. Hakuyusya (Tokyo) p. 354. (in Japanese) Our study elucidated that PRDA for lowland rice in Food and Agricultural Materials Inspection Center (FAMIC) 2013. Testing Methods for Fertilizers. Food and Agricultural the Sudan Savanna is effective, although it is affected Materials Inspection Center (Saitama, Japan) p. 370. by field conditions, such as water conditions. The lower Food and Agriculture Organization of the United Nations (FAO) price of local PR than TSP in Burkina Faso can make 2004. Use of phosphate rocks for sustainable agriculture. FAO Fertil. Plant Nutr. Bull. 13, FAO (Rome, Italy) p.148. cost effectiveness. Hammond, L. L., S. H. Chien, and A. U. Mokwunye 1986. Acknowledgments Agronomic value of unacidulated and partially acidulated phosphate rocks indigenous to the tropics. Adv. Agron. 40: The authors thank the entire staff of INERA and 89-140. Hamza, A. and E. A. Akinrinde 2016. Response of Sorghum JIRCAS for their technical support regarding field (Sorghum bicolor L.) to Residual Phosphate in Soybean- management and chemical analysis. Soil samples were Sorghum and Maize- Sorghum Crop Rotation Schemes on imported by the minister’s permission. Two Contrasting Nigerian Alfisols. Int. J. Agron. 1-9. Hien, V., S. Youl, K. Sanon, O. Traoré, and D. Kaboré 1992. Rapport References de synthèse des activités du Volet expérimentation du Projet Engrais Vivriers 1986-1991. Résultats agronomiques et Adesanwo, O. O., M. T. Adetunji, and S. Diatta 2012. Effect of évaluations économiques des formules d’engrais à moindre legume incorporation on solubilization of Ogun phosphate coût pour les céréales. p.184. (in French) rock on slightly acidic soils in SW Nigeria. J. Plant Nutr. Soil Jones, A., H. Breuning-Madsen, M. Brossard, A. Dampha, J. Sci. 175: 377-384. Deckers, O. Dewitte, et al. (eds) 2013. Soil Atlas of Africa. Ankomah, A. B., F. Zapata, S. K. A. Danso, and H. Axmann 1995. European Commission, Publications Office of the European Cowpea varietal differences in uptake of phosphorus from Union (Luxembourg) p.176. Gafsa phosphate rock in a low-P Ultisol. Fertil. Res. 41: 219- Leon, L. A., W. E. Fenster, and L. L. Hammond 1986. Agronomic 225. potential of eleven phosphate rocks from Brazil, Colombia, 106 Trop. Agr. Develop. 64（2）2020

Peru, and Venezuela. Soil Sci. Soc. Am. J. 50: 798-802. 2019-2020. Morris, M., V. A. Kelly, R. J. Kopicki, and D. Byerlee 2007. Fertilizer Sanchez, P. A., and C. A. Palm 1996. Nutrient cycling and use in African agriculture Lessons learned and good practice agroforestry in Africa. Unasylva 47: 24-28. guidelines. Directions in development, agriculture and rural Sikora, F. J. 2002. Evaluating and quantifying the liming potential of development. 39037. The World Bank (Washington) p.145. phosphate rocks. Nutr. Cycl. Agroecosyst. 63: 59-67. Nakamura, S., M. Fukuda, R. N. Issaka, I. K. Dzomeku, M. M. Smalberger, S. A., U. Singh, S. H. Chien, J. Henao, and P.W. Buri, V. K. Avornyo, E. O. Adjei, J. A. Awuni, and S. Tobita Wilkens 2006. Development and validation of a phosphate 2016. Residual effects of direct application of Burkina Faso rock decision support system. Agron. J. 98: 471-483. phosphate rock on rice cultivation in Ghana. Nutr. Cycl. Somado, E., R. G. Guei, and N. Nguyen 2008. Module 1: Overview: Agroecosyst. 106: 47-59. Rice in Africa. In: NERICA: The New Rice for Africa—a Nakamura, S., M. Fukuda, F. Nagumo, and S. Tobita 2013a. Compendium (Somado, E.A. et al. eds.) Africa Rice Center Potential utilization of local phosphate rocks to enhance rice (Bouaké, Côte d’Ivoire) pp.1-9. production in sub-Saharan Africa. Jpn. Agr. Res. Quart. 47: Trompette, R. 1989. Phosphorites of the northern Volta Basin 353-363. (Burkina Faso, Niger and Benin). In: Phosphate deposits Nakamura, S., T. Imai, K. Toriyama, S. Tobita, R. Matsunaga, M. of the world. Vol. 2. Phosphate rock resources. (Notholt, A. Fukuda, and F. Nagumo 2015. Solubilization of Burkina Faso J. G., Sheldon, R. P., and Davidson, D. F. eds.) Cambridge phosphate rock through calcination method. Jpn. J. Soil Sci. University Press (Cambridge) pp. 214-218. Plant Nutr. 86: 534-538. Yoshida, S. and Y. Hayakawa 1970. Effects of mineral nutrition on Nakamura, S., R. N. Issaka, I. K. Dzomeku, M. Fukuda, M. M. tillering of rice, Soil Sci. Plant Nutr. 16: 186-191. Buri, V. K. Avornyo, E. O. Adjei, J. Awuni, and S. Tobita 2013b. Van der Velde, M., C. Folberth, J. Balkovič, P. Ciais, S. Fritz, I. Effect of Burkina Faso phosphate rock direct application on A. Janssens, M. Obersteiner, L. See, R. Skalský, W. Xiong, Ghanaian rice cultivation. Afric. J. Agric. Res. 8: 1779-1789. and J. Peñuelas 2014. African crop yield reductions due Nziguheba, G., S. Zingore, J. Kihara, R. Merckx, S. Njoroge, A. to increasingly unbalanced Nitrogen and Phosphorus Otinga, E. Vandamme, amd B. Vanlauwe 2016. Phosphorus consumption. Global Change Biol. 20: 1278-1288. in smallholder farming systems of sub-Saharan Africa: Weil, S., P. E. H. Gregg, and N. S. Bolan 1994. Influence of soil implications for agricultural intensification. Nutr. Cycl. moisture on the dissolution of reactive phosphate rocks. In: Agroecosyst. 104: 321-340. The Efficient Use of Fertilizers in a Changing Environment: Rajan, S. S. S. and B. C. Marwaha 1993. Use of partially acidulated Reconciling Productivity and Sustainability. Occasional Report phosphate rocks as phosphate fertilizers. Fert. Res. 35: 47-59. No. 7. (L. D. Currie, L. D. and Loganathan, P. eds.) Fertilizer Rajan, S. S. S., J. H. Watkinson, and A. G. Sinclair 1996. Phosphate and Lime Research Centre, Massey University (Palmerston rocks for direct application to soils. Adv. Agron. 57: 77-159. North) pp. 75-81. Sanchez, P. A. 2002. Soil fertility and hunger in Africa. Science 295: