Influence of Organic and Mineral Fertilizer on Soil Proprieties and Performance of Rice (Oryza sativa) in Casamance, Senegal ()
1. Introduction
Rice is a staple food in Africa. From 2008 to 2018, rice production in Sub-Saharan Africa doubled, while consumption continued to rise exponentially [1]. Senegal is the third largest importer of rice in Africa, behind Nigeria and South Africa [2]. The calorific intake of rice is estimated at 31%, while production covers only 28% of the country’s needs, exposing the country to vulnerability and food insecurity [3] [4]. Despite the government’s efforts to increase the area under cultivation and improve production, yields are still low to meet the demand of an ever-growing population [5]. Most of the production of the most consumed crop depends largely on the quality of the soil and especially on the availability of nutrients in the soil. This availability has been ensured for many years by the application of chemical fertilizers. An insufficient application of nutrients and poor soil management, combined with harsh climatic conditions and other factors, have contributed to soil degradation, including soil fertility depletion [6]. However, the continued use of chemical fertilizers leads to the degradation of the chemical and physical properties of the soil, biological activities [7]. In addition, nutrients supplied exclusively from chemical sources, while initially improving yields, lead to unsustainable productivity over time. All these factors, combined with the high cost of chemical fertilizers and the low financial accessibility of small farmers, constitute the main obstacle to the use of chemical fertilizers, without taking into account the environmental pollution they generate.
The current energy crisis, with rising prices and the lack of an adequate supply system for inorganic fertilizers, requires more efficient use of organic fertilizers, green manures, crop residues and other sources to maintain yield levels and facilitate access for small-scale farmers [8]. The application of organic fertilizers has been demonstrated to improve crop growth by providing nutrients to plants as well as the physical, chemical and biological properties of the soil, creating a better environment for root development by improving soil structure [9]. However, improving soil quality to maintain agricultural yields will not be achieved without additional effort [10]. Organic fertilizers and optimized crop rotations foster the accumulation of organic matter in the soil [11] which in turn improves soil characteristics such as its infiltration and water retention capabilities [12]. According to [13] climate change is expected to negatively impact at least 22% of the cultivated areas of the world’s important crops, notably wheat and rice, one of the major contributors to food security. Since rice is a staple food for more than half of the world’s population [14], its productivity needs to be maintained by reducing yield gaps [15] to ensure the survival of populations in sub-Saharan Africa, particularly in Senegal, where its consumption is estimated at 90 kg/inhabitant/year [16] for a demand that is only met at 28% in the country. To cover this gap, it is crucial to transform our production systems and move towards agriculture capable of adapting to climate change while preserving soil quality and improving farmers’ livelihoods through the valorization of organic fertilization. The aim of this study is to assess the effect of organo-mineral fertilizers on soil chemical properties, rice development parameters and physiological and yield parameters.
2. Material and Methods
2.1. Study Area
The study was conducted in the experimental farm of the Agroforestry Department of Assane SECK University in Ziguinchor region. The experimental farm of Agroforestry Department is located at 12˚32'54.88'' North latitude and 16˚16'40.89'' West longitude (Figure 1). Ziguinchor region is characterized by an average annual rainfall of 1322.66 mm between 1984 and 2015 with a rainy season that extends from June to October and a Sudano-Guinean type of climate [17] and an average temperature of 27.10˚C.
Figure 1. Localization of trial and collected samples.
2.2. Vegetal Material
The plant material used in this study was the lowland rice variety Nérica L19, which had the dual advantage lacking in both parents (O. sativa and O. glaberrima). It combines the hardiness of the African species Oriza glaberrima with the productivity of the Asian species [18]. The development cycle of the variety is between 70 and 100 days after sowing and can reach a yield of 5T per hectare [19].
2.3. Fertilizer and Experimental Design
The fertilizers used were organic (Fertinova, Organova and Fertinova + Organova), mineral (NPK + Urea) and Control (without fertiliser). Fertinova is an organic fertilizer manufactured by the group “EléphantVert” and obtained by drying and sanitation poultry droppings which is rich in organic matter, macro and micro-nutrients. It is used as a foliar fertilizer. The 4-3-3 Fertinova formula was used, including 4% Nitrogen (N), 3% Potassium (K) and Phosphoric Anhydride (P205), 26% organic matter for a C/N of 12 and 20% moisture. Organova, mainly composed of 30% Organic Matter and 35% Moisture 35% is an organic fertilizer resulting from the composting of plant residues, livestock effluents and agro-industry co-products and developed by the group [20].
Organova and Fertinova were applied during the sowing phase with respectively 16 and 6 g. Fertinova + Organova was a combination composed by Organova (8 g/pot) and Fertinova (3 g/pot). For NPK + Urea, the 15-15-15 formula with 1.25 g/pot and Urea (0.9 g/pot) were use (Table 1).
Table 1. Composition of fertilizers.
Fertilizers |
Composition |
Fertinova (g/pot) |
Organova (g/pot) |
NPK (g/plot) |
Urea (g/pot) |
Fertinova |
16 |
|
|
|
Organova |
|
6 |
|
|
Fertinovat organova |
8 |
3 |
|
|
NPK + Urea |
|
|
1.25 |
0.9 |
Control |
0 |
0 |
0 |
0 |
A randomized complete block design with three replications was used in this experiment. A total of 15 elementary plots were carried out. The experimental design was 15 m long and 4.5 m wide with 67.5 m2. The blocks were separated from each other by alleys of 0.5 m.
Each block represented a repetition and included five elementary plots. The dimensions of the elementary plots were 2.25 m long and 1 m wide with 2.25 m2. Within each elementary plot, five pots were dug for better moisture conservation [21]. Eight seeds of Nerica L19 were sown in each pot. A direct sowing was carried out for 08 seeds of Nerica L 19 per pot. A thinning was done after germination to leave only one plant per pot.
2.4. Germination, Soil pH, Growth and Yield Parameter, Yield and Chlorophyll Content Were Measured
Germination, soil pH, growth and yield parameter, yield and chlorophyll content were measured.
Germination
Germination was obtained by direct counting of the number of emergences. The germination rate [22] was using the following formula:
.
Soil pH
Soil samples were taken at a depth of 10 cm depending on the fertilizers according to the duration for the initial, 15 and 35 days after sowing (DAS) and final phase of the rice cultivation. The soil samples were analyzed for soil pH using a pH meter.
Growth and yield parameters
The height of plants was measured using a centimeter and the number of tillers was counted at 60 DAS. The number of spikelets was obtained by direct counting at the phase of maturity.
Yield
The yield was calculated using the Lacharme formula [23]. The fresh plants were collected during the flowering phase and further dried at 60˚C in the oven for three days to obtain the weight of dry biomass. The 1000 grains and the dry biomass were weighed with an electronic precision balance (0.0001 g).
Chlorophyll content
The chlorophyll content of leaves was measured using a SPAD-502 Plus at the flowering stage of rice. Measures were taken in the morning at 07:00 am and the noon at 12:00 pm and were repeated for seven days on young, medium and old leaves.
2.5. Data Processing and Analysis
Collected data were processed and analyzed using R software [24] to evaluate the differences between the fertilizers. Analysis of variance (ANOVA) was done, and Tukey’s test was used to make multiple mean comparisons and detect the significant differences between the characteristics (fertilizers, duration, daytime, and stages of leaf development). Statistical significance was fixed at 0.05. All data were expressed as overall mean ± SE. Clustering based on Euclidian ecological distance, principal components analyses and correlations were done to study the relationships between soil pH, growth and yield parameters, yield and chlorophyll content and fertilizers.
3. Results
3.1. Germination
There was no significant difference (p = 0.485) between fertilizers. The overall germination rate was 98%. It varied between 87.5 ± 0.3 and 100 ± 0.0% depending on the fertilizer. In absolute value, the Fertinova (100 ± 0.0) and Fertinova + Organova (100 ± 0.0) fertilizers had the highest germination rate (Table 2).
Table 2. Variation of the germination rate according to fertilizers.
Fertilizers |
Germination rate (%) |
Fertinova |
100 ± 0.0a |
Fertinovat oganova |
100 ± 0.00a |
NPK |
87.5 ± 0.42a |
Organova |
87.5 ± 0.42a |
Control |
87.5 ± 0.30a |
p |
0.48 |
3.2. Soil pH
The evolution of pH over time revealed a significant decrease from initial (6.71 ± 0.01) to final (5.73 ± 0.04). The analysis of pH variance revealed a significant difference (p = 2e−16) between fertilizers. The highest pH was obtained with Fertinova + Organova and Fertinova (6.32 ± 0.05), followed by NPK + Urea (6.31 ± 0.05) and Organova (6.25 ± 0.05). The Control recorded the lowest soil pH (6.06 ± 0.07). The interaction fertilizers * duration influenced significantly (p = 0.000691) the soil pH variation. Fertinova + Organova obtained the highest pH (6.41 ± 0.03) at 15 DAS followed by Fertinova (6.34 ± 0.09). At 35 DAS, an increase in pH was observed in all fertilizers. At the end of the experiment, a decrease in pH was recorded for all fertilizers. Organova (5.92 ± 0.10) and Fertinova (5.84 ± 0.09) recorded the highest pH. The lowest pH (5.44 ± 0.06) was obtained with Control (Figure 2).
Figure 2. Soil pH evolution over time according to fertilizer.
3.3. Growth Parameters
The growth parameters (height, number of tillers and spikelets and length of panicles) varied significantly (p < 0.05) between fertilizers (Figure 3). NPK + Urea (98.6 ± 1.33 cm), Fertinova (94.73 ± 1.97 cm) and Fertinova + Organova (92.4 ± 3.78 cm) recorded significantly the highest plant height than Control (84.33 ± 1.39 cm) and Organova (77.53 ± 1.65 cm).
Figure 3. Variation of plant height (A), number of tillers (B), length of panicles (C) and number of spikelets (D) according to fertilizers.
The highest numbers of tillers were recorded on NPK + Urea (32.27 ± 4.19 cm) and Fertinova + Organova (23.27 ± 3.29 cm). However, the lowest number of tillers (9.60 ± 0.56 cm) was obtained on the Control. For the length of panicles, NPK + Urea (26.8 ± 0.60 cm) and Fertinova + Organova (26.46 ± 1.14 cm) recorded significantly larger panicles than organova (20.33 ± 0.38 cm) and Control (21.66 ± 0.71 cm).
Indeed, the number of spikelets under Fertinova + Organova (177 ± 18.76 cm) was significantly higher compared to NPK + Urea (126.67 ± 9.83), Fertinova (126.13 ± 10.99), Control (88.8 ± 4.27) and Organova (82.93 ± 2.57).
3.4. Yield
The analysis of 1000 grains weight showed no significant difference (p = 0.802) between fertilizers. However, NPK + Urea (25.84 ± 0.98 g) recorded the highest weight in absolute value compared to the other. The fertilizers influenced significantly (p < 0.05) the yield (Figure 4). The NPK + Urea (4.57 ± 0.90 tones ha−1) and Fertinova + Organova (4.51 ± 0.89 tones ha−1) recorded the highest yields. The lowest yields were observed at the Control (0.85 ± 0.05 tones ha−1).
For the biomass, NPK + Urea recorded the highest biomass (488.28 ± 60.83 g), followed by Fertinova + Organova (149.8 ± 46.68 g) and Fertinova (117.12 ± 10.65 g). However, the lowest biomass production was recorded in Control (64.44 ± 5.63 g) and Organova (84.84 ± 5.97 g).
Figure 4. Variation of 1000 grains weight (A), yield (B) and biomass (C) according to fertilizers.
3.5. Chlorophyll Content
Fertilizers influenced significantly (p < 2e−16) rice leaves chlorophyll content. NPK + Urea registered the highest chlorophyll content (29.36 ± 0.45 SPAD value), followed by Fertinova (27.78 ± 0.40 SPAD value), Organova (26.88 ± 0.47 SPAD value) and Fertinova + Organova (26.16 ± 0.55 SPAD value). Rice leaves chlorophyll content varied significantly according to daytime and development status. A higher chlorophyll content was observed at noon (27.96 ± 0.32 SPAD value) than morning (25.69 ± 0.30 SPAD value). The interaction fertilizers*daytime influenced significantly (p < 0.05) leaves chlorophyll content. However, the highest chlorophyll content was noted on NPK + Urea (30.4 ± 0.6) followed by Fertinova (28.4 ± 0.5) at noon. The lowest chlorophyll content was recorded on Control (21.5 ± 0.73) in the morning (Figure 5). For the leaves development status, young leaves (30.21 ± 0.35 SPAD value) recorded the highest chlorophyll content than medium (27.80 ± 0.37 SPAD value) and old (22.51 ± 0.38 SPAD value) leaves. However, analysis of variance showed a significant (p < 0.05) effect of the interaction fertilizers*leaf status on chlorophyll content. The highest chlorophyll content were recorded on Fertinova (32.50 ± 0.70 SPAD value) followed by NPK + Urea (32.25 ± 0.61 SPAD value) in young leaves. The lowest chlorophyll content was recorded on Control (19.24 ± 0.91 SPAD value) in old leaves (Figure 5).
3.6. Relation between Fertilizers, Soil pH, Growth and Yield Parameters, Yield and Chlorophyll Content
Clustering analysis revealed three groups according to the fertilizers. The first group was composed of Control and Organova, and characterized by very low chlorophyll content, growth and yield parameters and yield. The second group is constituted of NPK + Urea and favored high chlorophyll content, height, biomass and number of tillers. However, the last group composed of Fertinova and Fertinova + Organova and was characterized by higher yield, panicle length, number of spikelets and soil pH (Figure 6 and Figure 7). Principal component analysis (PCA) showed an overall positive correlation between agrophysiological parameters and yield. Yield was positively correlated with plant height, number of tillers, number and length of panicles, number of spikelets and 1000-grain weight, biomass and chlorophyll content. The number of tillers was also correlated with all
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Figure 5. Change in Chlorophyll content of rice leaves in responses to daytime (A), status of leaves development and fertilizers (B).
Figure 6. Cluster dendrogram of agrophysiological parameters between fertilizers of 1000 grains weight (A), yield (B) and biomass (C) according to fertilizers.
Figure 7. Principal component analysis of physiological parameters, yield parameters and fertilizers.
agrophysiological parameters except germination, where the correlation was zero. Chlorophyll content was strongly and positively correlated with biomass, pH, 1000 grain weight, plant height and number of spikelets. pH was positively correlated with all yield parameters and yield (Figure 8).
4. Discussion
Influence of fertilizer on soil pH
The results showed a significant variation in pH depending on the fertilizer used. This variation was observed during the development of the rice. Fertinova and Fertinova + Organova fertilizers recorded the highest pH while the lowest was noted for Control. Following the evolution of pH over time, an overall decrease in pH was noted from the beginning to the end of the experiment, except on day 35, when we noted a slight increase in pH for all fertilizers, excluding the Control. This could be explained by the reaction of the fertilizers some days after their application, coinciding with the release of nutrients for plants. This variation in pH, close to neutrality between the start of the experiment and 35 days, which is correlated with the development phase of the rice, favors good plant growth. Indeed, a pH close to neutrality is an asset for better nutrient uptake by the roots [25]. The relative decrease in pH from 6.4 to 5.2 can be explained by the waterlogging due to irrigation, which consequently generated acidification due to alternating flooding and drying [26]. Organic amendments increase soil pH compared to mineral fertilizers. The long-term addition of organic amendments increases the pH of acidic soils [27]. The application of Urea decreased the soil pH [28].
Influence of fertilizers on rice performance
The yield parameters (tillers, spikelets, panicles and panicle length and 1000 grain weight), dry biomass and paddy yield varied significantly according to fertilizers. NPK + Urea and Fertinova + Organova recorded the highest performance of rice. The agro-morphological parameters of the rice and yields are improved with the application of Urea [29]. However, the combination of Fertinova and Organova was a good alternative for soil improvement. Organova and Fertinova was used as a base and foliar fertilizers respectively. The combination of organic amendments played an important role by supplying required nutrients to the plant, particularly during the tillering and flowering phases. The application of Fertinova and Organova produced higher yields of tomato variety [21]. In addition to being easily accessible to smallholders, organic fertilizers ensured long-term sustainable rice production by preserving soil physicochemical parameters [30]. Indeed, organic amendments acted on soil structure by improving the soil’s retention capacity and consequently the balanced use of nutrients by plants [31].
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Figure 8. Correlation matrix for agro-physiological parameters, fertilizers and rice yields.
Influence of fertilizers on rice leaves Chlorophyll content
Results showed a substantial variation in chlorophyll content depending on the daytime and leaf status. The chlorophyll content observed at noon was significantly higher than in the morning. According to leaf status, chlorophyll content was highest in young leaves, followed by medium leaves and old leaves. A higher chlorophyll content on medium leaves of cucumber was recorded compared to old and young leaves [32]. The content of chlorophyll in leaves can be influenced by many factors such as leaf age, leaf position, and environmental factors such as light, temperature and water availability [33]. For the analysis also revealed that the highest chlorophyll content was recorded on NPK + Urea and Fertinova. The improvement in photosynthetic activity observed in NPK + Urea, Fertinova + Fertinova and Organova revealed the importance of mineral element availability on plant metabolism and physiology. The chlorophyll content in addition can be also influenced by cultivation practices and the nitrogen amount available for plants [34].
Conclusion
Increasing rice yields in the current context of climatic variability and degradation of agricultural soils required effective application of fertilizers. The results of our study revealed that soil chemical properties and rice performance were influenced by fertilizers. Organic fertilizers increased significantly soil pH. NPK + Urea and Fertinova + Organova recorded the best rice performance development and chlorophyll content. The chlorophyll content varied according to daytime and leaf status. The highest chlorophyll content was recorded at noon and in young leaves of rice. The application of fertilizers was an important element in improving soil pH and rice performance, the efficiency of fertilizer on rice yield.