Micro-Climate Conditions, Weed Diversity, Flowering and Yield of Young Cacao Plants as Affected by Shade Regimes

Abstract

Experiments were conducted in 2015/2018 in two cacao plots established in 2012 and 2013 in Akure, Nigeria to investigate micro-climate conditions, weed densities, flowering and yield of cacao as affected by shade regimes. Established cacao plots under three plantain (Musa spp) shade regimes consisting of No-shade, Moderate and Dense shade were used. Air and soil temperature, relative humidity and Photosynthetic Active Radiation (PAR), weed population and species diversity, cacao flowering and pod production were measured. From the results, air and soil temperature measurements under No-shade plots had a significantly higher mean values (320C) and soil (280C) compared with moderately shaded [air, 300C and soil, 26.50C] and densely shaded [air, 300C and soil, 260C] plots in 2015 and 2016 measurements but under 2017 measurements, no significant difference in the soil temperature of the plots under dense shade, moderate and the no-shade which were ascribed to canopy close-up of the cacao that led to reduced transmitted light through the canopy to the understories species. The vigour of weeds under no-shade plots were significantly higher compared with dense and moderately shaded plots. In 2013 established cacao plot, flower production was higher significantly in no-shade compared with those in moderate and dense shaded cacao plots in 2015 and 2016 measurement. Pod production under No-shade were significantly higher compared with other treatments in 2016 and 2017. Cherelle wilt rate was higher in shaded plots compared with the no-shade plots. Pod yield parameters were significantly higher under No-shade plots compared with shaded treatments during the three years of data measurement. Air temperature between 30oC to 33.7oC during flowering and fruit/pod setting was found to have positive influence on bean yield in cacao. The study concluded that excessive shade decreases yield of cocoa, while increases in temperature and relative humidity boosts some physiological processes for pod production in Cocoa. Introduction The farming process of cocoa can damage the environment itself through conversion of existing forest vegetation (deforestation) to cocoa plantation with less plant ecosystem diversity. Global climate change, for example, causes longer drought seasons making it more difficult for farmers to plant and sustain new cocoa trees. The impact of climate conditions on agricultural productivity is confirmed by many recent studies [1], [2], [3], [4] and [5]. They reported that decrease in water availability (moisture stress) during crop growing period could play a major role in reducing productivity. [6] examined the effects of rainfall on cocoa production and concluded that there are many interactions between weather variability and cocoa production. [7], [8] and [9] emphasized the significant of use of plantain as a shade plant for soil moisture conservation, temperature reduction and ecosystem stability in cacao plantation establishment. [10] proposed that changes in climatic extremes will constitute adverse impact on productivity of fruit harvests with likely agricultural losses of between 2 and 7% of Gross Domestic Product [11]. Efforts should be geared towards characterizing weathercrop relations, adopt sustainable management of water resources via adoption of water saving technologies, increased use efficiency of rainfall and soil water and identification and use of stress tolerant species [12]. Therefore, this research emphasised the effects of shade regimes on microclimate variation, cocoa flowering and yield in southwest Nigeria over three years (2015-2017). International Letters of Natural Sciences Submitted: 2020-02-24 ISSN: 2300-9675, Vol. 81, pp 31-41 Revised: 2020-05-20 doi:10.18052/www.scipress.com/ILNS.81.31 Accepted: 2020-05-29 CC BY 4.0. Published by SciPress Ltd, Switzerland, 2021 Online: 2021-02-25 This paper is an open access paper published under the terms and conditions of the Creative Commons Attribution license (CC BY) (https://creativecommons.org/licenses/by/4.0) Materials and Method Experiments were conducted between 2015 and 2018 on two established cacao plantations planted in 2012 and 2013 at the Teaching and Research farm of the Federal University of Technology Akure, Nigeria (Latitude 70 161 N and longitude 50 121 E of Greenwich meridian) in the rain forest agroecological zone. The variety of the cacao is CRIN Tc4 (Cocoa Research Institute of NigeriaTheobroma cacao) developed by Cocoa Research Institute of Nigeria. The two plantations were beside each other separated by a drive way. The size of the plots was 54 x 36 meters for both 2012 and 2013 established plots. The plots were established under three shade regimes of Moderate shade (30% shade) with one cacao row followed by one plantain row, dense shade (60% shade) with one cacao row followed by two plantain rows and No-shade (0 % shade) which is under open sun. The plantains and the cacao were planted at 3 meters apart both along the rows and across the rows. The number of cacao plant per shade treatment is 72 with the total cacao stands of 216 per experiment. Gravity drip irrigation was installed in both fields during the dry seasons to alleviate soil moisture stress. Weeding was conducted on the fields three times annually while minor pruning takes place annually before the onset of rain. During the experiment, twenty stands of cacao were selected from each shade regime from both fields totalling 120 cacao plants and were monitored from 2015, to 2018. Ten soil thermometers were installed per shade treatment at various point on the field to take the soil temperature at one week interval while Ten thermometers were also suspended under the canopy of the tagged cacao stands to measure the air temperature within the cacao canopy at varying periods of the day. Relative humidity and Photosynthetic Active Radiation (PAR) was also monitor. The relative humidity was measured using air moisture meter. The PAR was measured using DELTA T Sunscan Canopy Analyser. Data were also measured on flowering rate, cherrelle (immature young pod) production, cherrelle wilt, total pod yield, fresh pod weight, fresh bean weight, bean number per pod, dry bean weight, and total dry bean weight per shade regime. At one week interval, average air and soil temperature were taken with the use of thermometer on the selected cacao between the hours of 1.00-3.00 pm in the afternoon. Average soil temperature changes between the hours of 1.00-3.00pm were also recorded. At one week interval, cacao flowering, number of pods, number of Cherelles, and number of wilted Cherelles were monitored by counting. For the yield parameters, ripe cocoa pods were harvested at two weeks interval from the tagged cacao stands. Total pod yield and bean yield were determined by summing up the total harvested pods and bean yield at various harvest intervals. At harvest, weight of each pod was taken using weighing balance, the pods were broken with a blunt cutlass and the beans were extracted and weighed. The extracted beans were fermented and sundried to 7 % moisture and the weights were measured. At one month interval weed density sampling were taken using a 50cm by 50cm quadrant by throwing randomly under different shade regimes and the available weeds were sorted and classified into ephemeral, annual and perennial weeds. The total averages were recorded at the end of each experiment year. Microbial population (nematode, fungi and bacterial) within the soil under the varying shade regimes were also monitored during the experiment (2015, 2016 and 2017). Soil samples were from each shade regimes were analysed in the laboratory for nematode, fungi and bacterial. The total viable bacteria and fungi colonies were counted per gram of the soil samples while nematode count was carried out using Bearmann funnel method. The measured data were subjected to analysis of variance using MINITAB and the mean was separated using Tukey test. Results Figure 1 shows the effects of shade regime on monthly air temperature variation within the plots between May, 2015 and Nov. 2017. From the result, air temperature was significantly higher under no-shade compared to dense shade and moderately shaded cacao plots. No shade plots exhibits a significantly higher air temperatures during the months of October-December and February-May across the years of the experiment which was also associated with reduced soil moisture percentage. During the month of June –September and December/January, no significant different in the 32 ILNS Volume 81