Effect of Sowing Dates on the Productivity of Oilseed Citrullus Lanatus

Finding a sustainable solution to the problem of climate change is the first step to reduce food insecurity and malnutrition in developing countries. In Côte d’Ivoire the oilseed Citrullus lanatus constitutes a source of income for farmers. The lack of knowledge on the suitable sowing dates of this plant engenders it low production. Thus to resolve this problem, some field trial were carried out in Gbokora (Daloa). An experimental design with three blocs randomized was set up. Experimentation consisted to realize a sowing during two growing seasons: season 1 (S1) and season (S2). For each season five sowing dates separated with two weeks were realized: Early 1 (E1), Early 2 (E2), Middle (M), Later 1 (L1) and Later 2 (L2). It emerges from this study that to improve the yield of this plant, the crop should be grown during the first season. In addition, planting must be done between mid-March and the beginning of April. This period corresponds to the beginning of the rainy season in the study area. However, if the farmers wish to produce the plant in the second growing season, they will have to wait until the beginning of August, which corresponds to the short rainy season. sativus when is done at the beginning of the the of April. Similarly, in Iran, , showed that early planting maximizes the production of the Momordica charantia L. Such still unavailable for the oilseed Citrullus lanatus . The objective of this study is to evaluate the influence of sowing date on the production of this plant. The results of this study will allow producers of this cucurbit to revise their agricultural calendar and adapt it to the new climatic conditions.


Introduction
Finding a sustainable solution to the problem of climate change is the first step to reduce food insecurity and malnutrition in developing countries. According to Chebil, et al. [1] climate change is the increase in temperature and the variability of rainfall. This phenomenon is a major concern for both scientists and policy makers worldwide. These climatic variations have a direct impact on agricultural production, since agricultural systems depend in part on the nature of the climate [2,3]. This impact is particularly important in developing countries where agriculture is strictly dependent on rain without any alternative irrigation and is the main source of employment and income for the majority of the population [4,5]. With a traditional farming system, Côte d'Ivoire is not immune to these climatic disturbances. The situation is even more alarming in a peasant environment with a continuous decline in crop production. This is particularly the case of the oilseed Citrullus lanatus. It is regularly grown in the North, Central West and South of the country where it occupies an important place in agricultural activities. Highly prized in Ivorian societies, roasted and dough-processed seeds are used as ingredients in sauces during traditional ceremonies such as yam festivals and end-of-year celebrations. Also the work of Loukou, et al. [6] showed that these seeds are very rich in lipids, carbohydrates and proteins. In addition, Zoro Bi, et al. [7] also showed that dried and cleaned seeds are sold at 1500 FCFA against 600 FCFA for cocoa, thus constituting an additional source of income for producers. With advantages that present of this plant, it is imperative to increase production by developing a new cultural technique. Among the existing cultural approaches, sowing date plays an essential role because it allows plants to benefit from optimum temperature and rainfall conditions. Thus, in Nigeria the work of Eifediyi and Remison [8] showed that production of Cucumis sativus L. increases when sowing is done at the beginning of the rainy season, clearly in the month of April. Similarly, in Iran, Shirzad, et al. [9] showed that early planting maximizes the production of the Momordica charantia L. Such information is still unavailable for the oilseed Citrullus lanatus. The objective of this study is to evaluate the influence of sowing date on the production of this plant. The results of this study will allow producers of this cucurbit to revise their agricultural calendar and adapt it to the new climatic conditions.

Plant Material and Experimental Design
The planting material was constituted of 900 plants of oilseed C. lanatus. The seeds of those plants were obtained from the cucurbit germplasm of the University of Nangui Abrogoua (Abidjan, Côte d'Ivoire). A medium seed size cultivar (NI119) of the indigenous oilseed C. lanatus widely cultivated in Côte d'Ivoire was selected. Experimental design was constituted of three blocks. Those blocks were determined in an area of 0.8 hectares. Each block measured 102 m x 26 m with five plots. The plot was 16 m x 20 m containing 30 holes at depth of 3 cm. The holes were arranged in rows at spacing of 4 m between and within rows. In order to improve the growth and production of fruits five sowing dates were performed during two growing seasons (table 1). To ensure proper stand, five seeds per hole were sown directly and thinned to one plant per hole at the two-leaf stage. All plants per treatment including control were investigated. Any fertilizer or irrigation was applied during the trials. Weeds were manually controlled and the crop was sprayed with insecticide (Cypercal EC 50) to protect the crop against cucumber beetle, Zonocerus variegatus and lady beetle identified in study site.

Data Collection and Statistical Analysis
Yield (seeds dry weight ha) and 6 agronomical traits identified as yield components in oilseed cucurbits C. lanatus [10] were collected. The yield components measured included: plant vine length (PL); number of fruits per plant (NF), number of seeds per fruit (NS); seeds weight per fruit (SW); and 100-seeds weight (100-SD). Significant effect of sowing date and growing seasons were tested with ANOVA. When a significant effect is found for a factor, each parameter was examined by using the software SAS statistical package. In case of a significant difference the Least Significant Difference (LSD) multiple range-tests were used to identify the means those differ. Table 2 shows that the year of culture factor is not significant (P = 0.291). Which means the production of this cucurbit does not vary from year to year, similarly to the year interaction of culture x date of sowing (P = 0.283). On the other hand, the crop season, sowing date and all other interactions are significant. In other words, the producer must take into account the growing season and the sowing date in order to have a better production. Since the growing year does not have a significant effect, the two-year test data were combined. Also, the two seasons being characterized by different rainfall, the sowing dates were analyzed separately. Finally, in this chapter the analysis of the results will be done according to the season of cultivation and the calendar of sowing for each season.

Influence of Growing Seasons on Yield and Its Components
Significant differences between the growing seasons were noted for the seven characters tested (Table 3). Of the seven characters, six have high values in the first season. These are seed yield, plant length, number of fruits, fruit weight, number of seeds and seed weight. Only the weight of 100 seeds recorded its high value in the second season.
In a farm setting, parameters such as the number of fruits, the number of seeds and the yield of seeds are of interest to producers. Thus, to make a good harvest in terms of seeds and fruits, they must realize the sowing in the first season of cultivation.

Effect of Sowing Dates on Yield and Its Components
Statistical test results from the first crop season data show a difference between the five planting dates for yield and its components ( Table 4). Very early (E1FGS) and early (E2FGS) seedlings simultaneously have high yield values, plant length and number of seeds. The highest values of number and weight of fruit were obtained from early planting (E2FGS). The large seeds were produced with very early planting (E1FGS). The weight of 100 seeds has the maximum value with late sowing (E2FGS). It is retained that the producers to have a better production of this cucurbit, will have to sow either March 15th or April 1st to the first season of culture.
With the exception of yield and plant length, the other five traits completely differentiated the five sowing dates for the second crop season ( Table 5). The high numbers of fruit, seed weight, weight of 100 seeds and number of seeds are from plots where planting was done very late (L2SGS). The weights of the fruits and the number of seeds have their maximum values with the sowing done very early (E1SGS).

Discussion
Determining an appropriate planting date is fundamental to improving the production of any crop [11,12]. Thus, the influence of sowing date on the yield and yield parameters of the oleaginous C. lanatus was studied during this experiment. The values of agronomic parameters tested are higher with sowing on March 15 (very early) and April 1 (early) during the first growing season. These two months mark the beginning of the rains in the study area. Under these conditions, very early and early planting benefited from the first rains of the year, favoring good germination and better plant development. Indeed, the work of Kortse and Oladiran [13] showed that when C. lanatus seedlings are grown during the rainy season the plants remain vigorous and give high yield. The importance of rain in the success of the culture of C. lanatus is also known by the farmers. The study conducted by Munisse, et al. [14] in three producing localities of this species in Mozambique showed that farmers plant at the beginning of the rainy season. It is the same for the producers of C. lanatus in Benin [15]. In addition, Nerson [16] and Erdem and Yuksel [17] showed that rain is an indispensable factor in ensuring a better yield of C. lanatus. Otherwise, it should be pointed out that for very early planting, the period of intense fruit setting and fruit filling occurring between the 45th and 60th day after sowing coincides with the beginning of May [7,18,19]. This month is characterized by less violent rainfall, which prevents the fall of female flowers. In consequence a result, the plants were able to produce a large number of fruits containing a lot of seeds, which would have allowed relatively high yields to be recorded. When the number of fruits per plant and seeds per fruit are high in Cucurbitaceae, the yield is high [16]. The increased yield of Brassica campestris (L.) was explained by the high numbers of fruit per plant, the number of seeds and the weight of 1000 seeds [20]. In fact, these variables are referred to as the major components of yield for several crops [21]. Apart from yield, during this growing season, very late and late sowings recorded low values. Also, the very early and early sowing made it possible to have the best fruit weights and the number of seeds. Regarding the weight of seeds and the weight of one hundred seeds, they gave high value both with late and early sowing. This result suggests that seed quality is not influenced by the amount of fruit harvested. In other words, the plants form of oilseed C. lanatus would ensure their survival or reproduction by two major strategies. On the one hand during periods of stress (scarcity of rain and available resources), cucurbit adopt the R strategy, that is, they allocate all of their available resources for the perpetuation of the lineage. In these conditions, they produce very little fruit. On the other hand, they adopt the K strategy, that is to say when the environmental conditions are optimal [22]. These results could be a basis for reflection for geneticists or breeders in the search for genes resistant to drought.
During the second growing season from July to December, high yields were recorded with the late August 1 sowings. This season is less rainy and starts with the month of August [23]. The high values of the parameters could be explained by the rapid completion of the vegetative phase of the plants before the end of the rainy periods. The establishment of a dense vegetation cover during the appropriate period has created a moist microclimate at the feet of plants [24]. This moisture would have contributed to fruit development and seed filling [25]. In addition, flowering and fruiting occurs in early October when rains are less frequent, which prevents falls of female flowers. Indeed, Miah, et al. [26] found that torrential rains during flowering of crops lead to lower yields.
However, the yield of the first growing season is higher than that of the second growing season. The yield difference observed between the two growing seasons is related to the amount of rainfall recorded during the first growing season (516.6 mm versus 343.73 mm in the second season).
Such an observation was made by Khan, et al. [27] and Fatondji, et al. [28] on this same species. In fact, they indicated that the first growing season is more productive than the second season. In the study area, the measured parameters failed to differentiate between the two crop years. Such result was recorded by Sogut and Arioglu [29] on the plants of Beta vulgaris. They explained this result by the small variation of the rainfall and the temperature from one year to another.

Conclusion
The determination of the sowing dates is an essential phytotechnical approach that contributes to the improvement of crop production. In the farming community, lack of attention to this production factor has often led to lower crop yields. This is particularly the case for oilseed crops in rural areas in the tropics. The present study was initiated for the determination of an appropriate date of sowing of the oilseed Citrullus lanatus. It appears from this study that to improve the yield of this plant, the crops should be grown during the first season. In addition, planting must be done between mid-March and the beginning of April. This period corresponds to the beginning of the rainy season in the study area. However, if the farmers wish to produce the plant in the second growing season, they will have to wait until the beginning of August, which corresponds to the short rainy season.