EFFECTS OF WEEDING REGIME ON SEEDLING GROWTH PERFORMANCE OF THREE COCOA (THEOBROMA CACAO L.) VARIETIES IN TWO CONTRASTING ECOLOGIES OF NIGERIA

Abstract

Cocoa (Theobroma cacao L.) is in the family Malvaceae (formerly Sterculiaceae), originated from Central and northern South America. It is now distributed and grown throughout the tropical world with Cote D’Ivoire, Ghana, Nigeria and Cameroon in this order, leading in world production. In Nigeria, Cocoa was a major agricultural export crop and a top foreign exchange earner in the 1950s and 60s prior to the discovery of crude oil in commercial quantities in the 1970s. To-date in Nigeria, cocoa farming is a way of life, and the cocoa business a main source of revenue and means of livelihood to people from cocoa-growing places. Chocolate produced from cocoa beans is used as an essential ingredient in numerous commercial products, including candy, desserts and drinks. High quality soap using potash from cocoa pod husk, Cocoa-kola beverage, Cocoa enriched gari, Choco-Ogi, Choco-bread and Cocoa powder for health drink over the years has been developed by Cocoa Research Institute of Nigeria (CRIN) who has the official mandate to work on cocoa production and development. Weeds are undoubtedly one of the major factors limiting cocoa cultivation; Weeds compete for light, nutrients and moisture, shading of cocoa seedlings, weed competition with shade plant for cocoa, climbing and ‘’choking’’ of cocoa plants, poor plantation establishment, low early yield and pod losses. The young state of cocoa when the canopy is yet to close, has been identified as one of the most critical stages when weed incidence is severe in Nigerian cocoa plantations. Therefore, there is a need to implement environment - friendly weed control methods which assure optimum cocoa establishment and sustainable yield and quality; hence weeding regime in this study. To this end, ield experiments were conducted during the 2014, 2015 and 2016 rainy season (June-October) in two contrasting rainforest ecologies viz, the Cocoa Research Institute of Nigeria (CRIN), Ibadan (Lat. 7° 10' N, Long. 3° 52' E,), Oyo State and CRIN, Owena (70 11ʹ N, 50 01ʹ E) Sub - station, Ondo State, to examine the effects of weeding regime on seedling growth performance of three cocoa (Theobroma cacao L.) varieties. The experiments were arranged as a split plot using a Randomised Complete Block Design (RCBD) and three replications per treatment. The main plot treatments comprised three varieties of cocoa (CRIN Tc1; CRIN Tc2; Local F3 Amazon) and the sub-plot treatments had 10 periods of weed interference in two sets combined in the same field. In one set of the treatments, plots were kept weed-free for 1, 2, 3 and 4 months after transplanting, and subsequently left weed-infested (WF-UW) within the same year’s rainy season. In the other set of treatments, plots were left weed-infested for the corresponding periods and subsequently kept weed-free (UW-WF). In the two control treatments which did not vary, the plots were kept weed-free (treatment 5) and weed-infested (treatment 6) throughout. Plantain was used as a shade crop for the cocoa stands and was established a year before transplanting cocoa at a spacing of 3 x 3 m (ditto for cocoa) and three stands of cocoa covering 3 x 6 m = (18 m2)/treatment was used. Data were collected on rainfall and mean temperature; soil analysis before planting; weed growth characteristics [weed cover (%), weed flora composition (family, taxa, growth form), weed density (no. /m2), weed dry weight (g/m2), weed relative importance value, RIV(%), weed occurrence (%)]; and cocoa morphological parameters involving plant height (cm), stem girth (cm), leaf production (no./plant), branch production (no./plant) and leaf area (cm2/plant). The results showed that weed flora composition before establishment in Ibadan had 34 weed species, 18 families with Asteraceae (20.59%, 7 species) and Poaceae (17.65%, 6 species) and two growth forms, viz. annual broadleaves (41.18%, 14 species) and perennial broadleaves (29.41, 10 species). At Owena, it had 23 weed species and 15 families dominated by Asteraceae (17.39%, 4 species) and Convolvulaceae and Poaceae (13.04%, 3 species) and annual broadleaves (43.48%, 10 species) and perennial broadleaves (PBL) (26.09, 6 species). Weed species diversity varied widely with crop varieties, location and weeding regime over the three years of study. Weed flora was more diverse across crop varieties and locations in 2014 than in 2015, and apparently not diverse in 2016. Weed flora was most diverse in Tc2 than in F3 Amazon and Tc1. The weed flora recorded in Owena was more diverse than in Ibadan across the cocoa varieties. Tc2 was most severely invaded by extremely diverse weed flora at Owena in 2015. The WR1 (W1 + UW4) had the most diverse weed flora across variety and location in June and July. Both Tc1 and Tc2 severely suppressed weed flora diversity at Ibadan and Owena in 2016. Chromolaena odorata was most prevalent across the cocoa varieties and locations in early 2014 (June to July), followed by Desmodium scorpiurus and Pouzolzia guineensis. In 2015 and 2016, more weeds were encountered but their prevalence depended on cocoa variety and time of cocoa development. Generally, the most prevalent weeds were Chromolaena odorata, Desmodium scorpiurus, Pouzolzia guineensis, Cyathula prostrata, Oplismenus burmanii and Synedrella nodiflora. In conclusion, Tc1 and Tc2 produced more vigorous seedling than F3 Amazon, despite the higher weed density and weed covers in Tc1 and Tc2. Cocoa seedlings produced significantly better growth in Owena than Ibadan. UW1 + WA4 was most efficient in weed suppression, thus resulting in better seedling growth than other weeding regimes. It is recommended that UW1 + WA4 was the most effective weeding regime for cocoa seedling establishment under the conditions of this study, especially for Tc2 at both Owena and Ibadan.