Response of Quality Protein Maize to the Synchronization of Application and Needs for NPK Fertilizer in Acid Soils of the South-West of the DR Congo ()
1. Introduction
Maize is one of the important cereal crops grown in the DRC and spreads out from the forest to the savannah. Its production in the savannah of southwestern DRC has moved from a minor crop to a major and commercial cereal crop in competition with cassava and rice crops in the country’s economy [1].
The released Quality Protein maize (QPM) varieties have a high grain yield potential. They are friendly processed, easy to digest and of low cost compared with other cereals. Its versatility makes it a widespread crop adapted to a wide range of agro-ecological zones. Maize, as a typical cereal, responds favorably to the application of fertilizers, especially in the savannah, where the soils are generally not very fertile [2] [3]. It has a strong depleting effect on the soil and it is generally observed that it does not produce a good grain yield in the plots without fertilizer application [4]. According to Useni et al. (2013) [5], inadequate plant nutrition management and low soil fertility are the main factors responsible for lower yields.
In most experiments, the response of maize to nitrogen (N) is very significant [6]. In a continuous farming system, nitrogen fertilizer is the most important nutrient for maize production. Savanna soils are also deficient in native phosphorus (P) [6] [7]. The appropriate use of inorganic fertilizers (NPK) on crops led to increased yield where there was substantial nutrient depletion [6] [8] [9] [10].
Compared with normal maize, QPM has higher nutritional quality as it contains double the amount of lysine and tryptophan and no changes in other amino acids except a lower level of leucine [11]. Since this maize was recently introduced into the country, it has been the subject of several agronomic studies [12] [13] [14] [15] including fertilization in the acid soils of southwestern DRC [6].
Experiments on planting density and basal fertilization rate have been carried out [6] and [13]. However, accurate data on the appropriate period of the basal fertilizer application have not been made available so far. Several options for basal fertilizer application can be used: 1) before sowing, 2) at sowing and 3) after emergence. The period of inorganic fertilizer (NPK) application is then the most important factor influencing the growth, development and yield of maize crops. The aim of this experiment was to find out the right time of basal fertilizer application for QPM enhanced production in acid savannah soils in southwestern of DRC.
2. Materials and Method
2.1. Experimental Site
The trial was conducted on acid soil at the INERA Mvuazi Research Center during two cropping seasons: A (October 2019 to February 2020) and B (mid-March 2021 to mid-May 2021). Mvuazi is located at 14˚54' East longitude and 5˚21' South latitude, at an altitude of 470 m. The soil of Mvuazi belongs to the Sudano-Guinean climatic zone of type Aw4 [16]. This soil is characterized by low organic matter content and low water holding capacity, resulting in low nitrogen availability [1] [17] and Orthic feral soil type [18] (Table 1).
2.2. Climate Data
Figure 1 presents the evolution of climate data during the two experimental seasons (2019-2021).
2.3. Materials
The factorial design with three replicates and three factors was used. The first factor included three dates of NPK application. The second factor included four maize varieties including two of quality protein maize (Mudishi-1 and Mudishi-3) and two of normal maize (Samaru and unimproved Local variety). The third factor comprised of two seasons. Plot sizes were 5 m × 1.5 m, made up of two central rows with spacings of 0.75 m × 0.50 m.
Fertilization with mineral fertilizers was done on the basis of mineral fertilizer NPK 12-24-12 at sowing, i.e., zero-day after sowing (0 DAS), fifteen days after sowing (15 DAS) and thirty days after sowing (30 DAS). Urea (46%) was applied using the microdosing method. The microdosing consisted of a localized application of NPK fertilizer (3 g/hill) or 160 kg/ha and Urea (1.125 g/hill) or 60 kg/ha [6]. Urea was applied in two halves respectively at 15 DAS and 30 DAS.
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Table 1. General physico-chemical properties of Mvuazi soil.
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Figure 1. Evolution of climatic parameters (rainfall, maximum temperature and minimum temperature).
2.4. Method
Sowing with three seeds per hill was done after mechanical ploughing, harrowing and cleaning of rubbles, followed by thinning at emergence, leaving two plants per hill for a density of 53,333 plants per hectare [13] [19] [20].
Data were gathered on the growth parameters: plant height (Ph), ear height (Eh), percentage of stem lodging (Sl), percentage of root lodging (Rl), plants aspect (Pasp), phenological parameters: days at 50% male flowering (Poll), days at 50% female flowering (Silk) and Anthesis and silking interval (ASI), disease parameters: ear rot (Erot) and production parameters: ear aspect (Easp) and grain yield (Yld) [21] [22].
2.5. Statistical Analyzes
Data collected were processed and submitted to the analysis of variance according to the general linear model (aov(y~fact1*fact2*fact3)) of the agricolae package of the statistical software R 3.6.3. The separation of the means at the threshold of 0.05 was made by the test of the least significant difference (LSD) of the same package. The principal component analysis (PCA) carried out using the Factominer and foctoextra package of the R 3.6.3 software made it possible to establish correlations between response variables and group individuals into groups of similarities.
3. Results and Discussion
3.1. Analysis of Variance
The analysis of variance was carried out on the data and measurements collected on the growth and production variables. Corresponding results are presented in Table 2 and Table 3. Results analysis showed that there were highly significant effects of the season (p < 0.0001), the date of application (p < 0.0001), and the variety (p < 0.0001) on male and female flowering. The height of the plants as well as that of the ear was influenced by the season. With regard to the production variables, highly significant differences were observed for yield according to the seasons and dates of fertilizer application (p < 0.0001). However, a significant difference was observed in the interaction between season and variety.
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Table 2. Effects of factors studied on growth parameters.
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Table 3. Effects of the factors studied on the production parameters.
3.2. Growth Parameters
Male flowering at 50% (poll): the highest number of days at 50% male flowering was observed in the local variety on the 15th day after sowing and this difference was significant (p < 0.0001) for the effects of seasons, date of application, varieties and season*variety interaction with the variety Samaru which recorded 48 days to reach 50% male flowering when NPK is applied on the 30th day after sowing. The number of days to 50% male flowering decreased with delay in fertilizer application beyond 15 days after sowing.
Female flowering at 50% (Silk): Samaru variety reached 50% of female flowering at 53.3 days after sowing, which was earlier than the local variety with 50% female flowering at 72 days when NPK application was done 30 days after sowing. As for male flowering, the number of days to 50% female flowering decreased with increasing NPK fertilizer application time beyond 15 days after sowing, but the difference was highly significant (p < 0.0001) for the interaction effects between seasons and varieties.
Anthesis and silking Interval (ASI): the higher number of days of interval between male and female flowering was observed in the local variety with 8.33 days at 15 days after sowing compared with the Mudishi-3 variety which recorded an ASI of 1.33 days when the application of fertilizers is done at 15 days after sowing. The difference was highly significant (p < 0.0001) for season and variety effects.
Plant height (Ph): plant height was greater in the local variety (262.73 cm) under the application of NPK fertilizer 15 days after sowing in season B and the lowest value was observed in the Samaru variety (225.13 cm) for the same season. As for season A, the greatest plant height was recorded in the Mudishi-3 variety (218 cm) when NPK fertilizer was applied at sowing, compared with the Samaru variety (172.83 cm) for the NPK fertilizer application 30 DAS in season A. The difference was highly significant (p < 0.0001) for season effects and significant (p < 0.05) for date*variety effects.
Ear height (Eh): the highest value for ear height was observed in the local variety (161.40 cm) for the application of NPK fertilizer at 30 days after sowing, in contrast to the variety Mudishi-3 (121.60 cm) for NPK supply at 15 DAS in Season B. The Mudishi-3 (121.86 cm) variety recorded the highest value of Eh when NPK fertilizer was applied at sowing in Season B. A, against the local variety (85.60 cm) when NPK fertilizer was applied at 15 DAS. These results show that there was a highly significant difference (p < 0.0001) for the seasonal effects and a significant difference (p < 0.05) for the various effects (Table 2).
3.3. Production Parameters
Plant aspect (Pasp): performance on plant aspect was excellent (score 1) for most treatments. However, this aspect of the plants was less good (score 3) for the local variety when the fertilizer application was applied 15 days after sowing in season A. There was a highly significant difference (p < 0.0001) for the effects of variety and season*variety interaction (Table 3).
Harvested plant rate (Pharv): a significantly high harvested plant rate (97.77%) was found in Mudishi-3 variety during season A under the application of NPK fertilizers at 30 DAS, compared with the local variety which recorded a low rate (40.14%) of plants harvested for the same treatment. On the other hand, in season B, this rate was higher for Samaru variety (92.98%) and lowered in the local variety (47.94%) for the application of NPK fertilizer at 15 DAS. The effects of variety strongly (p < 0.00001) influenced the results for the rate of plants harvested (Table 3).
Ears aspect (Easp): the best aspects (score 1) of the ears were observed in all the varieties under different application periods of the NPK fertilizers except the local variety (score 4) when the NPK fertilizer was applied at 15 and 30 days after sowing in season A. The variety and season factors significantly (p < 0.0001) influenced the aspect of ears (Table 3).
Ear rot score (Erot): the ear rot score was high (score 4.33) in the Mudishi-1 variety under the application of fertilizers at 30 days after sowing in season A. The difference between the averages was highly significant (p < 0.0001) under the effect of the season. However, the interaction effects of season and variety significantly influenced (p < 0.05) the rating of rot. This rating decreased with the variety and in season B (Table 3).
Grain yield (Yld): average grain yield was high in Mudishi-1 (7.90 t/ha) and Mudishi-3 (8.0 t/ha) varieties when fertilizer was applied at sowing time in season A while the local variety recorded an average of 3 t/ha for the same treatment. In general, yield decreased with late application of fertilizer after sowing and in season B; season B was shorter than season A. The difference was highly significant (p < 0.0001) with respect to the effects of season, fertilizer supply date and variety (Table 3).
3.4. Principal Component Analysis (PCA)
The principal component analysis showed that only the first two dimensions had an eigenvalue greater than one. These two dimensions alone produced 74.82% of the variations. The first dimension is characterized by growth variables (male flowering and female flowering) and the appearance of plants and ears. As for the second dimension, it is characterized by the height of the plants and the insertion of the ear as opposed to the yield and the rate of plants harvested. The high values of the athesis and siliking interval (ASI) are opposed to the production parameters (Pharv and Yld) (Figure 2).
Figure 3 shows a grouping of varieties around treatments (date of fertilizer application and seasons). Figure 3 showed that the local variety, being unimproved, deviated from the remainder of the average parameters studied for this variety and joined the large values of ASI, Pasp, Easp, silk and poll in all seasons.
The high values of the production parameters are recorded in season A, mainly for the application of fertilizers at sowing time.
4. Discussion
In general, the application of NPK as basal fertilizers promotes plant growth and increases the grain yield of maize varieties in acid soils [6] [9] [23]. In this study, the average growth variables as well as those of production were mostly influenced by the season, the date of fertilizer application and the varieties. The improved varieties exhibited better performance in terms of plant quality and grain yield.
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Figure 3. Variables, individuals and factors studied map.
The date of basal fertilizer application has previously been studied by [9] and [24]. They concluded that the NPK application at sowing is very advantageous if it is not followed by a dry period. Otherwise, applying the NPK within 10 days after emergence is suitable and any delay in the application is detrimental to production. These results are similar to those found in this study, which shows that NPK applied 15 days after sowing significantly reduce growth performance and negatively affects grain yield.
Mudishi-3 variety has appeared to tolerate late application of basal fertilizers and got an acceptable average production in season A. These hypotheses were verified by [25], showing that this variety had a very low-stress sensitivity index (SSI) and as a result, its yield remained stable under the drought conditions occurring in the middle of the growing season.
The low values of the production variables recorded in season B can be due to corresponding rainfall and thermal episodes recorded during the experiment (Figure 1). The short periods of intense rainfall causing vicious droughts at the end of the main cropping season disrupting maize productivity, have been reported by [26]. This phenomenon, combined with the delay in the application of basal fertilizers, may explain the weak performance of maize in the short rainy season. This situation was reported by [27].
According to Useni et al. (2013) [5], inadequate plant nutrition management and low soil fertility are the main factors responsible for lower yields. This opinion is in accordance with the fact that a maize crop that does not receive nutrients during its phase of growth and organ development ends up with a significant productivity decrease [1] because the absorption of certain major elements such as P and K is done continuously starting the first days of the maize cycle [28] [29] [30].
5. Conclusion
The objective of the present study was to determine the best date of basal fertilizer application for the production of QPM in the acid soils of the savannah in the southwestern zone of DRC. Two varieties of QPM were compared to two varieties of normal maize in a factorial design replicated three times during two seasons. The results obtained showed that the application of NPK basic fertilizers leads to maize plants high-performance with a high grain yield. In addition, the application of fertilizers at sowing time favors a faster maturing for the improved varieties of QPM compared with the unimproved local variety. The application of NPK basal fertilizers at the time of sowing promotes a high rate of harvested plants which therefore decreases with the delayed nutrient supply. The reductions in yield are very significant when the inputs are applied after 30 days from the start of the cycle in a short growing season.
Acknowledgements
We would like to thank the entire team of scientists and technicians who authored this article. They gave their precious time to contribute to the implementation of this study despite their numerous duties. We appreciate the truthful and sincere collaboration which exists between the three research institutions (INERA) and universities (UPN and UNIKIN) which made this experiment successful under the ASARECA Climate Smart Agriculture Alliance (ACSAA).