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.