Pineapple [Ananas comosus (L.) Merrill] is an important tropical fruit that belongs to the family Bromeliaceae (Bartholomew et al., 2003).The fruit is consumed in Nigeria mainly in fresh form as fruit salad and as juice extracted from fresh fruits. Pineapple is a long gestation crop with initial slow growth during establishment phase. The resultant lack of immediate returns on investment in the first year of cropping and challenges associated with management of the wide spaces between the rows of pineapple, pose serious challenge to farmers. Thus, the utilization of the resources within the wide spacing of pineapple rows during the early growth phase need to be addressed. Sole crop of pineapple may not efficiently use the growth resources (light, water and nutrient) during its early / initial slow growth and development. Intercropping pineapple with short duration food crops such as pepper (Capsicum spp), with upright growth habit and cowpea (Vigna unguiculata) may enhance the efficiency of resource use during the production cycle, food and income for farmers. This is in addition to diversified production, reduced dependency on one crop and spreads of labour and income (Uriza et al., 2005).

 

Appropriate timing and scheduling of the growth phases in which the component crops interact and share resources on the field will enhance the efficiency of resource utilization and productivity of the intercrops (Olubode et al., 2012). The stage of growth of the main crop (pineapple) and the first minor component crop (pepper) at which cowpea, a crop characterized by spreading growth habit is introduced is critical as this practice will determine the intensity of the competition among the intercrop components. It is therefore imperative to determine the appropriate time to sow cowpea into the pineapple-pepper intercropping system in order to minimize competition and enhancement of productivity. The growth and yield of crop species response to the available environmental resources and stress factors of the growing season differ as there are variations in prevailing soil and climatic environments at different seasons of sowing (Agele and Olabomi, 2010). This study, therefore sought to determine the effects of time of sowing cowpea into pineapple-pepper intercrops on growth and yield of pineapple in a pineapple-pepper-cowpea based intercropping system.

 

Experiments were conducted at two locations in Akure (Lat: 7^o14^ꞋN and long: 5^o11^ꞋE), a humid rainforest zone of Nigeria during the rainy and late seasons of 2011 and 2012. The meteorological data of the study area revealed a bimodal rainfall distribution pattern with highest rainfall recorded in 2012 as shown in Table 1. Composite soil samples of the experimental sites were analyzed and result presented in Table 2. The rainy-season planting experiments were conducted at the Experimental Station of the Federal College of Agriculture, Akure (FECA), while the late-season planting experiments were conducted at the Teaching and Research Farm, Federal University of Technology, Akure.

Four experiments based on additive series intercropping system adopted pineapple as the main crop with pepper and cowpea as the minor intercrop components. The experiments designed to evaluate the effect of varying the time of sowing cowpea into pineapple-pepper based intercropping system were laid out as a randomized complete block design with three replications and cowpea were sown into pineapple-pepper intercrops at three-week intervals in addition to pineapple-pepper intercrop alone and sole crop components (pineapple, pepper and cowpea).

 

In the rainy-season planting experiments, cowpea were sown into pineapple-pepper intercrops simultaneously with the transplanting of pepper into pineapple and at 3, 6 and 9 weeks after transplanting (WAT) pepper seedlings into pineapple in addition to pineapple-pepper intercrop alone cowpea and the sole crops of pineapple, pepper and cowpea. The late-season planting comprised sowing cowpea at the time of transplanting pepper seedlings into pineapple and at 3 weeks after transplanting pepper seedlings into pineapple, pineapple-pepper intercrop alone and sole crop components (pineapple, pepper and cowpea). The population density of the minor intercropped components (pepper and cowpea) was maintained at lower population densities of 54 and 62.5 % of their sole crop.

 

Double row system of planting pineapple was adopted with spacing of 90 x 60x 30cm (60cm between each double row; 30cm within the rows and 90cm between two double rows). The suckers of pineapple (smooth cayenne variety) were cured and planted on 2^nd May and 29^th August, for the 2011 rainy and late season experiments. Pineapple suckers were planted on 18^th May and 18^th August for the 2012 rainy and late season experiments. The centre of the wider spaces between the two-double rows were planted with five weeks old pepper seedlings at 60cm apart while the spaces within each double rows of pineapple were alternated for planting of pepper and cowpea separately. Cowpea cultivar (Ife brown) characterized by semi-erect growth and intermediate maturity period was sown at two seeds per stand into the spaces between the transplanted pepper and the adjacent row of pineapple in the wider spaces and at the centre of the space within double rows that were not planted to pepper at 50 cm apart.

 

Cowpea seeds were sown into the intercropped plots on 9^th and 31^st May, 21^st June and 2^nd July 2011 respectively for the rainy season experiment while cowpea seeds were sown on 8^th and 28^th September for the 2011 late season experiment. Likewise, cowpea seeds were sown into the intercropped plots on 19^th May, 9^th June, 30^th June and 21^st July respectively for the 2012 rainy season experiment while cowpea seeds were sown on 10^th August and 12^th September for the late season experiment.

 

Induction of flowering in pineapple was carried at 13-14 months after planting (MAP) with Ethrel (2-Chloroethylphophonic acid) a plant growth regulator and ethylene producing hormone to stimulate uniform flowering. The ethrel solution was prepared by dissolving 30 mls of ethrel paste and 150 g of urea fertilizer in 20 litres of clean water in a knapsack sprayer and thoroughly agitated into homogeneous solution.  About 50 mls of the homogeneous solution was dispensed into the centre of the pineapple leaf rosette to ensure accumulation of the solution at the leaf axils for contact with the abaxial epidermis close to stem apex for a period of time. This procedure was adopted following the report by Turnbull et al. (1993). The vegetative growth of pineapple was assessed using the D-leaf as growth indicator. The leaf area of pineapple D-leaf, the youngest fully physiologically mature leaf on the plant and also the longest growing leaf on the plant (Petty, 2006; Pineapple News, 2008) was estimated from the length and width of the leaf at 3 to 10 MAP. Based on the triangular shape of the leaves, the leaf area of the pineapple D-leaf was estimated as:

D-leaf area = ½ * b*h.

where b and h are the width and length of the D-leaf respectively.

 

Two pineapple plants were uprooted per plot at the end of intercropping phase and the biomass were separated into various components (leaves, stem and root), weighed and oven dried to constant weight at 105 °C. The number of days to 50 % inflorescence initiation after flowering induction was monitored and fruit yield and yield components were determined. The yield parameters measured were fruit girth, weight of whole fruit, weigh of fruit without crown, crown weight and fruit yield. Data collected were subjected to analysis of variance using Statistical Analysis System version 9 (SAS, 2003) and means separated using Tukey’s Honestly Significant Difference (HSD) test at 5% probability level.

 

Table 3 shows the temporal trends of the D-leaf area which differed significantly between 32 and 40 WAP in the rainy season of 2011. Sowing cowpea early into the intercrop resulted in significantly lower D-leaf area. Sowing of cowpea early at the time of transplanting pepper produced lowest leaf area. However in the late season planting of 2011, the D-leaf area was not significantly influenced by the time of sowing cowpea. The D-leaf area measured at the various sampling dates was not significantly influenced by time of sowing cowpea into pineapple-pepper intercrop in rainy and late season of 2012.

The pineapple biomass (dry weights of pineapple leaves, stem, root and total plant biomass) measured at post-intercropping were not significantly influenced by the date of sowing cowpea into pineapple-pepper intercrops in both experiments (2011 and 2012, Table 4).

The number of days to 50 % flowering in pineapple decreased with delayed introduction of cowpea into pineapple-pepper intercrop in the rainy season planting of 2011 and 2012 (Table 5). Although not significantly different from other sowing dates, sowing cowpea at the time of transplanting pepper into pineapple in the rainy season planting in 2011 prolonged the number of days to 50% flowering by 28 days. When cowpea was sown at the time of transplanting pepper into pineapple in the rainy season of 2012, the number of days to 50% flowering was shorter. The time of sowing cowpea into pineapple-pepper intercrops did not significantly influence the number of days to 50 % flowering for the late season experiments of 2011 and 2012.

The girth of pineapple fruits was not significantly influenced by the date of sowing cowpea into pineapple-pepper intercrops except when cowpea was sown at the time of transplanting pepper into pineapple in the rainy season of 2012. The weight of pineapple fruit (fruit without crown) was significantly influenced by the time of sowing cowpea into pineapple-pepper intercrop in the rainy-season planting of 2011 when the weight of pineapple fruit was significantly reduced when cowpea was sown at the time of transplanting pepper into pineapple (Table 5). Delayed sowing of cowpea into pineapple-pepper intercrop by 3 to 9 weeks resulted in up to 280% increase in weight of pineapple fruit. However, the weight of pineapple fruits was not significantly decreased with early sowing of cowpea into pineapple-pepper intercrop in rainy season of 2012. The weight of pineapple fruit reduced significantly when cowpea was sown at the time of transplanting pepper into pineapple in the late season of 2012. The weight of whole fruit of pineapple was significantly reduced when cowpea was sown at the time of transplanting pepper into pineapple in the rainy season of 2011 (Table 5). The weight of pineapple fruit + crown was not significantly influenced by the date of sowing cowpea into pineapple-pepper intercrops in the late season of 2011. Conversely, the values of this parameter reduced significantly when cowpea was sown at the time of transplanting pepper into pineapple in the late season of 2012. Pineapple fruit yield of 12.8 t/ha obtained when cowpea was sown at the time of transplanting pepper was 71.4, 69.8, 72.8 and 71.4% lower than fruit yield obtained when cowpea was sown at 3, 6 and 9 WAT and in sole crop of pineapple, respectively. The time of sowing cowpea into pineapple pepper intercrops in the rainy season of 2012 did not result in significant decreases in pineapple yield (Figure 1). However, sowing cowpea early at transplanting pepper and at 3 WAT pepper reduced fruit yield by 25.1 and 12.8 %, respectively. The yield of 78.5 t/ha of pineapple fruit recorded in sole pineapple was not significantly higher than fruit yield in the pineapple-pepper intercrop alone and pineapple-pepper intercrops with cowpea sown at transplanting and at 3 WAT pepper in the late season of 2011 (Figure 1). About 17.5 % yield reduction occurred when cowpea was sown at time of transplanting pepper into pineapple in the late season of 2011. Yield reduction of 39.2 % was however recorded when cowpea was sown at the time of transplanting pepper into pineapple in the late season of 2012.

The temporal effect of the presence of cowpea on fruit yield of pineapple in pineapple-pepper-cowpea intercrop is described by polynomial functions (Figure 1). The relationships were characterised by variable R² in the 2011 and 2012 rainy and late season experiments

Rainy season of 2011: y = – 2.9482x² + 25.782x – 5.2556, R² = 0.82**

Late season of 2011: y = 0.55x² – 2.1176x + 68.872, R² = 0.54*

Rainy season of 2012: y = 0.258 x² + 1.2463x + 44.311, R² = 0.50*

Late season of 2012: y = – 1.9363x² + 20.254x + 44.311, R² = 0.94**

 

The decline observed in the growth indicator (area of d-leaf) of pineapple when intercropped with pepper and cowpea resulted from shading effect of pepper and cowpea on pineapple as explained by Bartholomew et al. (2003). The effects of shade and competition was more noticeable when cowpea was sown early especially at the transplanting pepper in the rainy season planting of 2011. The lack of significant differences in growth and biomass accumulation obtained for this treatment can be due to the initial slow growth of pineapple during the establishment phase which coincides with phase of intercropping with pepper and cowpea. Lower values of pineapple d-leaf area recorded for the late-season planting could be attributed to unfavourable weather condition of this season on the establishment of pineapple. The late season is characterized by low rainfall, high temperature and low relative humidity which cumulate in terminal drought situation (Agele et al., 2008).

 

The number of days to 50% flowering in pineapple was prolonged when cowpea was sown at the time of transplanting pepper during the rainy season and could be attributed to the shading by the biomass and canopy of the more vigorous cowpea. However, the number of days to 50% flowering was not significantly prolonged in the late-season crop due to shorter duration of the arable intercropped. Py et al. (1987) reported that the state of the crop species population density enhanced competition at the period of flowering is of profound significance.

 

The lower yield of pineapple fruits obtained when cowpea was sown at the time of transplanting pepper into pineapple, especially for rainy season planting of 2011, is attributable to its competition resulted from the effect of competition with component crops (pepper and cowpea). The vigorous growth of cowpea and its extended vegetative phase impacted the pineapple growth and yield when it was sown at the time of transplanting pepper completely shaded pineapple. The lower yield of pineapple could have stemmed from the unfavourable weather condition during the following dry season which reduced the plant vigour. The impacts of the intercropping decline with time and resulted in little difference in fruit yield between sole pineapple and pineapple-pepper-cowpea intercrops. Fukai and Trenbath (1993) reported that the late maturing component crops in intercropping as in the case of pineapple may be affected by the presence of the associated crop, but a long time period for further growth after the harvest of the component crops ensures full use of available growth resources.

 

The vigour of cowpea growth in the rainy season planting of 2012 was lower when compared to that of rainy season experiment of 2011; this could have enhanced growth and yield of pineapple due to reduced competition and shading. Sowing cowpea early in the late-season planting in 2012 resulted in high cowpea vigour and subsequently lower fruit yield of pineapple. The higher pineapple fruit yield obtained in the late season experiments could be attributed to reduced competition resulting from shorter growth duration of intercropped cowpea and the rapid senescence and interfering cowpea biomass. Uriza et al. (2002) concluded that with a good crop management high fruit yield and quality of pineapple could is obtainable intercropping.

 

The vigorous growth, extended vegetative phase and enhanced competition by cowpea and pepper impacted the pineapple growth and fruit yield. The impacts of the intercropping on pineapple declined with time with respect to the period of recovery growth after the harvest of intercrop component crops and availability of resources especially when cowpea was sown late into the intercrop. Delayed sowing of cowpea into pineapple-pepper intercrop resulted in higher pineapple fruit yield and yield components. Delayed sowing of cowpea into pineapple-pepper intercrop reduced the effect of intercropping on growth and yield of pineapple. Higher fruit yields was obtained in the late-season planting due to reduced competition as result of shorter duration of intercropping phase. Hence, delayed introduction of cowpea into pineapple-pepper intercrop between 3 to 9 weeks in the rainy-season planting and 3 weeks after transplanting pepper in the late-season crop would ensure that farmers obtain high yield of pineapple close to what is obtainable under sole pineapple in addition to additional income from cowpea and pepper at the establishment phase of pineapple while the cropping system achieves higher efficiency of resource utilization.

 

Agele S.O., and Olabomi A., 2010, Growth, fruit set efficiency and blossom end rot in Capsicum spp in humid Southwest Nigeria. Applied Tropical Agriculture, 15:112-124

 

Agele S.O., Adeniji I.E.,  Alabi I.A., and Olabomi A., 2008, Responses of growth, yield and N use efficiency of selected tomato cultivars to variations in the hydrothermal regimes of the cropping seasons in rainforest zone of Nigeria, Journal of Plant Interactions 2(4): 273-285

 

Bartholomew D.P., Paull R.E., and Rohrbach K.G., eds., 2003, The pineapple: botany, production and uses. CABI publishing, Wallingford, UK, Pp1-301

 

Fukai S., and Trenbath B.R., 1993, Processes determining intercrop productivity and yields of component crops, Field Crops Research, 34: 247-271

 

Olubode O.O., Aiyelaagbe I.O.O., and Bodunde J.G., 2012, Responses of Sunrise-solo pawpaw, okra and cucumber components of pawpaw based intercropping system to time of intercropping, Scientia Horticulturae, 139: 71-78

 

Petty G.J., 2006, Pineapple “D-leaves“- useful indicators of plant health and growth status in the smooth cayenne cultivar. In: Pineapple Newsletter, Newsletter of the Pineapple Working Group, International Society for Horticultural Science, 13: 35-36

 

Pineapple News, 2008, Newsletter of the Pineapple Working Group, International Society for Horticultural Science, 15: 3-4

 

Py C., Lacoeville J., and Teisson C., eds., Maisonneuve et Larose G.P., and, 1987. The Pineapple cultivation and uses. Techniques Agricoles Et Productions Tropicales. Paris France, SAS, 2003, Statistical Analysis System Version 9.3.1. SAS Institute Inc., Cary NC. USA

 

Turnbull C.G.N., Nissen R.J., Sinclair E.R., Anderson K.L., and Shorter A.J., 1993, Ethepon and causes of flowering failure in pineapple, Acta Horticulturae, 334: 83-88

 

Uriza A.D.E., Rebolledo M.A., and Rebolledo M.L., 2005, Short cycle crops intercropped with pineapple: an option to increase productivity, Acta Horticulture 666 (Abstract)