JCBPS; Section B; February 2021 –April 2021, Vol. 11, No. 2; 396-406, E- ISSN: 2249 –1929 [DOI: 10.24214/jcbps.B.11.2.39606.]

Journal of Chemical, Biological and Physical Sciences

An International Peer Review E-3 Journal of Sciences Available online atwww.jcbsc.org Section B: Biological Sciences

CODEN (USA): JCBPAT Research Article Evaluation of nutrients (N, P, K) limiting maize (Zea mays L.) yield in two agro-ecological zones of the southern-central of .

Arona Sonko1,2*, Ndèye Yacine Badiane Ndour2, Moussa N’Diénor2, Aliou Faye3, Niokhor Bakhoum4 & Saliou Ndiaye1

1 Ecole Nationale Supérieure d’Agriculture, Université Iba Der Thiam de Thiès, B.P A296 - Thiès – Sénégal. 2 Laboratoire National de Recherches sur les Productions Végétales, Institut Sénégalais de Recherches Agricoles, Bel Air, Route des Hydrocarbures, BP 3120 - Dakar - Sénégal. 3 Centre National de Recherches Agronomiques de Bambey, Institut Sénégalais de Recherches Agricoles, BP 53 CNRA – Bambey - Sénégal. 4 LMI LAPSE, Laboratoire Commun de Microbiologie IRD/ISRA/UCAD, Centre de Recherche de Bel Air, BP 1386, CP 18524 – Dakar - Sénégal.

Received: 24 February 2021; Revised: 17 March 2021; Accepted: 30 March 2021

Abstract: Cereals response to nutrients varies according to soil characteristics in sub-Saharan Africa. Thus, subtractive trials were conducted to identify the major nutrients (N, P, K) limiting maize yield in Senegal central south (Nioro site) and east (Sinthiou Malème site) soils. In each zone, we set up a randomized complete block experiment on station with 4 replicates and on farm in 5 scattered fields. The following treatments were evaluated: non-fertilizer (T) control, completely fertilized

with NPK at high doses (150N-40P2O5-40K2O kg/ha), and three other treatments (PK, NK, NP) resulting from the successive omission of one element from the NPK. Soil nutrients analysis revealed, at Nioro station, a N deficiency associated, in Nioro farm, with that of P and K. However, in Sinthiou Malème, N and P deficiencies were noticed. Application of NPK increased the grain yield between 143 % and 543 % compared to the control. At Nioro, the grain yield was limited only by N on station, but by both P and K on farm. Regarding Sinthiou Malème the grain yield was

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reduced by N and P starvation. Our study suggests that an optimal use of fertilizers could sustainably enhance maize productivity in Senegal. Moreover, the adaptation of the fertilization recommendation according to the site is necessary. Keywords: Maize yield limitation, Mineral fertilizers, Nutrient deficiency, Soil fertility, Subtractive trials.

INTRODUCTION

Soil degradation is a major problem for agriculture in Sahelian regions, leading to land abandonment due to yield regularly reducing after several years. In addition, cultural practices such as cereal/fallow rotation, used to restore the nutrients in cultivated fields[1], is replaced by the cereal/peanut rotation without fallow or adequate use of fertilizers[2]. Soil degradation thus comes from the imbalance of the nutrient statement induced by rainfall variability, cultural practices and demographic pressure. Nutrients exportation through crops depletes the soil and exacerbates the soil erosion, leaching and thus their degradation. In Senegal, the average annual nutrient deficit due to nutrients exportation is estimated at 12N-2P-10K kg/ha [3]. In this context, maize yields are low even if they rich 1000 kg/ha to 1500 kg/ha in the study areas. Thus, they still lower compare to the optimal level evaluated to 3000 kg/ha to 4500 kg/ha on farm [4]. Achieving optimal yield for a given variety requires better use of fertilizers. Yet, the same mineral fertilizer dose was recommended in Senegal whatever the zone. Several studies have shown that mineral fertilizers improve soil fertility and crop yields [5]. Challenge remains to adjust the contribution of mineral fertilizers to the soil nutritive supply taking into account the balance of nutrients to sustainably improve soil fertility management. Indeed, the variability of soil fertility affects the efficiency of fertilizer use in Maize cultivation [6]; it is crucial to adapt the formulation recommendations to specific soil and climatic conditions. This study sought to identify the nutrients (N, P, K) that could limit maize productivity. Aim was to assess subtractive effects of N, P or K on "Suwan-1" maize cultivar yields under central south and east pedoclimatic conditions of Senegal.

MATERIAL AND METHODS

Study site presentation: Three villages were chosen from Nioro site in the agroecological zone (AZ) of the south-central groundnut basin and from Sinthiou Malème site in the AZ of Eastern Senegal. Daga Sekko, Paoskoto and Nioro were selected in Nioro located in , in . Groundnuts and millet are the dominant crops. Groundnuts is rotated with cereals (millet, maize). Dominant soils are of tropical ferruginous type with little or without leaching on sandy-clayey sandstones located on the glacis. They have a sandy texture to sandy loam with good to average drainage. Guiri Gara, Sinthiou Damba, and Sinthiou Malème were selected in Sinthiou Malème located in department, in . Groundnut and millet are the main crops, but cotton, whether or not rotated with maize, is also present, and sorghum as well. Peanut is also in rotation with cereals (millet, maize, sorghum). Dominant soils are gravel type reworked on cuirass and tropical ferruginous leached on colluvio-alluvial material respectively encountered on glacis and terraces. They have a sandy to sandy clay texture with medium to low drainage. Soil physicochemical characteristics of the study sites were presented in Table 1. Both zones are characterized by a dry tropical climate of Sodano-Sahelian type with a rainy season from June -

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October and a dry season from November - May. Climatic conditions of the study sites were represented by the Figure 1.

Figure 1: Nioro (a) and Sinthiou Malème (b) weather conditions during 2014 rainy season. Tmin: Minimum temperature, Tmax: maximum temperature. Arrows indicate, from left to right, start of sowing, start of female flowering, start of harvest.

Experimental design: A network of agronomic trials was carried out on the experimental station of the Senegalese Institute of Agricultural Researches (ISRA) and on farm in both study sites. Experiments set up in stations were under fallows above three years old in Nioro and over a long period in Sinthiou Malème. However, groundnut was previously grown on farms in the two sites. The experiment set up in station was a randomized complete block with four replicates. Each block consists of six elementary plots of 36 m2 (6 m * 6 m) separated from each other by alleys of 1.5 m. Factor studied was mineral fertilizer with five modalities resulting from the combination of different doses of nitrogen (N), phosphorus (P) and potassium (K). Complete fertilizer (NPK) treatment consists of high doses of N, P and K. From the NPK treatment, a fertilizing element (N, or P or K) was subtracted each time to form three other treatments (PK, NK, NP). A non-fertilizer (T) treatment was added as a reference control. N was supplied in the form of urea (46 % N), P in the form of double superphosphate (25 % P2O5) and K in the form of potassium chloride (60 % K2O). Dose of the NPK treatment was 150 kg N/ha, 40 kg P2O5/ha and 40 kg K2O/ha,

PK treatment is 0 kg N/ha, 40 kg P2O5/ha and 40 kg K2O/ha, NK treatment was 150 kg N/ha, 0 kg

P2O5/ha and 40 kg K2O/ha and NP treatment was 150 kg N/ha, 40 kg P2O5/ha and 0 kg K2O/ha. The maize mineral fertilizer dose recommended in Senegal whatever the zone, is 122 kg N/ha, 30 kg

P2O5/ha and 30 kg K2O/ha. Experiment in farms was made up of complete randomized blocks dispersed among various representative farm fields. All the treatments were applied on each farmer field. A total of five farmer fields were selected both at Nioro site (3 at Daga Seko, 2 at Paoskoto) and at Sinthiou Malème site (3 at Sinthiou Damba, 2 at Guiri Gara). Soil and crop management: "Suwan-1" maize cultivar, recommended in the study zones, was used with a grain yield of 4500 kg/ha on farm and a development cycle of 90 days [4]. Manual sowing was carried out between 12 - 20 July with 3 grains per pocket at a depth about 3 cm. Rows were spaced of 75 cm where pockets were 25 cm in each row. The thinning was done, by leaving one-plant-per- pocket, 12 days after sowing (DAS) to obtain a density of 53,333 plants/ha. Four manual weeding operations are carried out: weeding in 12 DAS, two other weeding and one hilling during the application of fertilizers in 25, 39 and 54 DAS, respectively. The fertilizer was applied around the hole about 5 cm from the base of the plants and buried to a depth of about 7 cm. Phosphorus,

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Evaluation… Arona Sonko et al. potassium and 20% nitrogen were applied 25 DAS. Remaining nitrogen (80%) was applied to the after 39 and 54 DAS in equal quantity. Data collection and analysis: Daily weather data (rainfall, temperatures, solar radiation) were collected with an automatic weather station CIMEL type at the two experimental stations of ISRA located at Nioro and Sinthiou Malème. Composite soil was sampled from each block over 0 - 20 cm from the top before setting up the trials. A quantity of 100 g of dry soil was sieved (2 mm) for further analyzes. Soil texture was determined by the Robinson Köln pipette method. Soil pH was measured in soil/distilled water suspension (1/2.5). Total carbon was determined according to Walkley and Black [7]. Total nitrogen was estimated by the Kjeldahl [8] method. Potassium was measured by spectrometric determination in flame emission and CEC from the exchangeable base extraction solution. Phosphorus was determined by following Olsen [9] method. Maize grain and straw yields for each treatment were determined from a 9 m2 designed in each elementary plot central part. Grains and straw were harvested, dried by the sun then in an oven (65 °C) during 3 days at a humidity level of 0%. Relative grain yield and above ground biomass of the PK, NK and NP subtractive treatments were calculated as follows: 푃 푓푟표푚 푠푢푏푡푟푎푐푡푖푣푒 푋 푡푟푎푖푡푒푚푒푛푡 푃푅푋 = 푃 푓푟표푚 푁푃퐾 푡푟푎푖푡푒푚푒푛푡 Where X = represents the subtractive (PK, NK or NP) treatment. PRX = represent the relative grain yield or aboveground biomass from X subtractive treatment. When PRX is close to 1, the response to the subtracted nutrient becomes nil. Statistical analyses: Analysis of Variance (ANOVA) was carried out using R software, version 3.3.1. Tukey test was used for the separation of means at the probability threshold of 5 %. The response to nutrient subtraction was evaluated for each treatment using the 5 % t-test with 1 as the reference value.

RESULTS AND DISCUSSION

Weather conditions (rainfall, temperatures and radiation): Figure 1 presents the daily weather data (rainfall, temperatures and radiation). Cumulative rainfall recorded was 542.1 mm at Nioro and 693.5 mm at Sinthiou Malème. Annual rainfall appeared to be good, according to Diakhate[10] who estimates maize (120 days) water needs at least 420 mm of water. At Nioro, two rain breaks were noted from 201 - 216 calendar days and from 269 - 278 calendar days. Minimum temperature fluctuated between 18 - 26.8 °C and the maximum temperature between 28.6 - 44.7 °C. Radiation varied between 9.1 - 26 MJ/m2j. As for Sinthiou Malème, two rain breaks were observed from 201 - 210 calendar days and from 274 - 287 calendar days. Minimum temperature varied between 18.7 - 28.9 °C and maximum temperature between 28.2 - 44.5 °C. Radiation varied between 6 - 26.12 MJ/m2j. Trials temperature conditions are within the temperature range (15 - 44 °C) favorable to the good development of tropical maize [11]. Weather environment in Sinthiou Malème trials seems less restrictive for the development of maize cultivation than that in Nioro’s trials. Soil characteristics: All soil parameters analyzed were significantly different between trials (Table 1). Texture of both trial soils was sandy which is unfavorable for organic matter accumulation [12] but favorable to water infiltration. This may explain the low total carbon content (3.54 - 8.22 ‰) observed in all trial soils. It was well below the critical range (1.9 – 2.2 %) for maize production [13]. Likewise, total nitrogen content was low (0.18 - 0.49 %) in all trial soils and was depressed as 399 JCBPS; Section B; February 2021 –April 2021, Vol. 11, No. 2; 396-406. [DOI:10.24214/jcbps.B.11.2.39606.]

Evaluation… Arona Sonko et al. compare to the fertility scale defined by Dabin and Maignien [14]. Low total carbon contents combined with low clay levels and their kaolinic dominant mineralogy may explain the soils CEC values (1.75 – 9.14 meq/100g) which were overall less than 7 meq/100g, the critical threshold defined by Sanchez et al.[15] . This seems to indicate a low buffering capacity of the soils and limits the nutrient retention capacity with a high risk of leaching. Soil pH (4.80 - 5.65) was very acid in Nioro, but acid to moderately acid in Sinthiou Malème according to Muller and Gavaud [16]; it was demonstrated that soil pH below the critical value (5.5) affects the development and nutrition of various crops including maize [17]. Phosphorus content (5.0 - 12.8 ppm) was comparable to 12 ppm, the threshold defined by Vanlauwe et al. [18], on Nioro station but below in the remaining trial soils. Potassium concentration (0.06 - 0.11 meq/100g) was only below to the critical threshold (0.10 meq/100g) proposed by Sanchez et al. [15] on Nioro farm soil.

Table 1: Trial soils physicochemical characteristics of 0 - 20 cm top soil

Nioro Sinthiou Malème Parameter Station Farm Station Farm Clay (%) 2.81±0.29 c 6.19±0.45 a 4.62±0.72 b 2.92±0.76 c Silt (%) 2.95±0.32 b 6.31±1.05 a 5.87±0.62 a 5.83±1.43 a Sand (%) 94.2±0.47 a 87.5±1.45 c 89.5±1.30 bc 91.3±1.95 b pH 4.95±0.24 b 4.80±0.34 b 5.65±0.35 a 5.34±0.18 ab Total carbon (‰) 3.54±0.51 b 3.95±0.51 b 8.22±1.09 a 3.97±1.11 b Total nitrogen (‰) 0.21±0.07 bc 0.49±0.12 a 0.42±0.08 ab 0.18±0.06 c Phosphorus (ppm) 12.8±2.60 a 6.0±0.87 b 7.2±0.46 b 5.0±1.06 b Potassium (meq/100g) 0.11±0.01 a 0.06±0.01 b 0.10±0.03 a 0.10±0.01 a CEC (meq/100g) 4.12±01 b 9.14±2.16 a 2.00±0.16 bc 1.75±0.19 c

Mean±standard deviation. On one line, the different letters indicate a significant difference and the same letters, a non-significant difference at 5% threshold. CEC: cationic exchange capacity.

Subtractive treatments effects on grain and straw yields: Grain yield varied between 251 - 3449 kg/ha while the straw yield varied from 1111 - 4939 kg/ha (Table 2). The Tukey HSD test significantly distinguishes different groups of treatments according to the trials (Table 2). Compared to T treatment, NPK treatment increased grain yield between 143 - 543 % and straw yield from 47 - 202 % according to the trials. This confirm Diatta and Siband [19] who assert that the application of mineral fertilization in non-degraded soils in Senegal leads to a significant increase in yields. Fertilization, in addition to the soil's supply capacity, allows the crop to meet its nutritional needs by increasing mineral elements availability [20]. Subtraction of a nutrient from NPK resulted in different yield losses between trials. Subtraction of N (PK treatment) caused grain (20 - 72 %) and straw (23 - 45 %) yields losses. These losses were significant on station trials, but not significant on farm trials. Grain (12 - 76 %) and straw (0 - 55 %) yields losses due to P subtraction (NK treatment) were also observed. Only the losses observed on Nioro station were not significant. Subtraction of K (NP treatment) also led to grain (1 - 50 %) and

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Evaluation… Arona Sonko et al. straw (7 - 18 %) yields losses. These losses were significant only on Nioro farm for grain yield. This is why Pieri [21] asserts that fertilization plays a major role in improving soil productivity. Importance of mineral elements in crop growth and development has been proven through several research studies [22, 23]. Therefore, maize yield was limited in trial with soils depressed N, P and/or K nutrients.

Table 2: Treatment effects on grain and straw yields at different sites

Grains (kg/ha) Nioro Sinthiou Malème Treatment Station Farm Station Farm T 1132±25 b 942±323 c 772±318 b 251±289 c PK 996±212 b 1826±504 ab 9778±544 b 639±290 b NK 2501±446 a 1254±275 bc 820±435 b 540±158 bc NP 2827±339 a 1133±499 bc 2541±436 a 1525±182 a NPK 2851±445 a 2285±720 a 3449±784 a 1612±271 a P value 1.90x10-6 1.41x10-4 1.92x10-5 9.25x10-10 Straw (kg/ha) T 2654±271 b 2045±693 c 2362±389 b 1111±278 b PK 2277±163 b 3406±1023 ab 2948±213 b 1849±565 b NK 3894±172 a 2568±615 bc 2228±211 b 1676±200 b NP 3628±403 a 3329±687 ab 4152±784 a 2763±359 a NPK 3903±167 a 4425±364 a 4939±391 a 3353±368 a P value 1.70x10-6 9.75x10-5 2.59x10-6 7.32x10-7

Mean±standard deviation. On one line, the different letters indicate a significant difference and the same letters, a non-significant difference at 5% threshold.

Grain yield and aboveground biomass responses to the subtraction of a mineral nutrient from the complete fertilizer: Figure 2 represents the effect of N, P or K subtraction from NPK treatment on the relative grain yield and aboveground biomass of maize in Nioro (Figure 2a and 2c, respectively) and in Sinthiou Malème (Figure 2b and 2d, respectively). Relative grain yield and aboveground biomass obtained by subtracting N were significantly less than 1 in all the trials, except that one in Nioro farm. When P was subtracted, the relative grain yield and aboveground biomass recorded were significantly lower than 1 in all the trials except that one in Nioro station. Subtraction of K triggered a relative grain yield and aboveground biomass significantly lower than 1 only on Nioro farm. All these variable effects suggest that soil indigenous supply in P and K in Nioro station, in N in Nioro farm, and in K at Sinthiou Malème are adequate to meet maize production needs. Conversely, additional inputs of N on Nioro station, of P and K in Nioro farm and, of N and P in Sinthiou Malème are necessary in order to cover maize production needs. These observations imply that the sustainable management of soil fertilization must take into account the variability of their intrinsic fertility. Response to the applied mineral nutrients may become blurred with soils increasing fertility [24]. All this reflects a significant soil characteristics heterogeneity and crops growing conditions in the study sites.

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Figure 2: Relative grain yield (Nioro (a), Sinthiou Malème (b)) and aboveground biomass (Nioro (c), Sinthiou Malème (d)) when N, P or K is subtracted in NPK treatment. Values of the Y-axes close to 1 indicate a weak response to the absence in mineral fertilization of the nutrient considered. On the standard deviations, the asterisks indicate a significant response to the corresponding nutrient.

Correlations between relative grain yield and soil fertility status of N, P and K: Maize relative grain yield was strongly correlated, when the red marks are not taken into account, with the soil's N (Figure 3a), P (Figure 3b) and K (Figure 3c), respectively. All of these relationships were highly significant. Maize grain yield response to the subtraction of N, P or K tends to fade with increasing soil content nutrients. Furthermore, grain yield recorded the strongest responses to the absence of N and the weak responses to the absence of K on Nioro station and at Sinthiou Malème while the weak responses to the absence of N and the strongest responses to the absence of K were observed on Nioro farm. Likewise, the weakest responses of the grain yield to the absence of P were noted on Nioro station while the three other remaining trials obtained the strongest responses. These observations show different nutrient deficiencies linked to the soil fertility state in N, P and K. These nutrient deficiencies confirmed those suspected by inspecting nutrient contents in trial soils, as observed by Fosu-Mensah and Mensah [25]. Variation in the diverse cereals’ response to additional mineral nutrients is a consequence of the diversity of the balance of production resources between regions associated with a wide range of management practices and seasonal variability [26]. The most distant production factor limits the use of others that are still available for the crop [27]. Sillanpää [28], studying the nutrient deficiencies of 190 soils from 15 developing countries, finds that 85%, 73% and 55% of these soils were deficient in nitrogen, phosphorus and potassium, respectively. Furthermore, the significant linear correlations observed reveal that 57%, 65% and 77% of the aboveground biomass responses are explained by the soil contents in N, P and K, respectively. This suggests that soil K appears to be the most important fertility indicator followed to a lesser extent by P. Samaké et al. [29] indicate that soil nitrogen and potassium are important indicators of soil fertility in West Africa.

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Figure 3: Relationship between relative grain yield in the absence of N (a), P (b) or K (c) in NPK treatment and the inherent soil fertility (nitrogen, phosphorus or potassium respectively) of the different trials. Significant correlations are marked by one (P <0.05), two (P <0.01) and three (P <0.001) asterisks.

CONCLUSION

Knowledge of soil mineral nutrients that limit agricultural productivity is crucial for developing strategies for the sustainable management of soil fertility. Our study shows a difference in soil mineral nutrients deficiencies for "Suwan-1" maize depending on the site. This demonstrated that the fertilizer doses to be applied into the soil must essentially target the raising of the level of fertility, precisely the correction of deficiencies in order to optimize maize productivity. Soil fertilization options in Nioro farm must ensure that P and K and, to a lesser extent, N deficiencies are amended. On the other hand, on Sinthiou Malème farm, the fertilization options must prioritize to raise the level of N and P and, to a lesser extent, K in the soil by adding specific fertilizers. This study suggests the optimization of fertilizers use and will contribute to the soil fertilization management in Senegal. Furthermore, study work which compares increasing doses of N, P and K, combined with the use of appropriate agronomic models, would make it possible to identify the optimal doses to be applied to the soils of various crop-growing agroecological areas in Senegal.

ACKNOWLEDGEMENT

Authors gratefully acknowledge West Africa Agricultural Productivity Program (WAAPP) for financial assistance for research and African Plant Nutrition Institute (APNI) for translation of this article.

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Corresponding author: Arona Sonko, Ecole Nationale Supérieure d’Agriculture, Université Iba Der Thiam de Thiès, B.P A296 - Thiès – Sénégal

Online publication Date: 30.03.2021

406 JCBPS; Section B; February 2021 –April 2021, Vol. 11, No. 2; 396-406. [DOI:10.24214/jcbps.B.11.2.39606.]