Fertigation through trickle and micro sprinkler on flowering characters in cocoa ( Theobroma cacao L . )

An experiment was conducted during 2010 and 2011 to investigate the impact of fertigation on flowering characters of cocoa at Tamil Nadu Agricultural University, India. The study was laid out in randomized block design with thirteen treatment combinations replicated thrice. The study shown that, fertigation with 125% recommended fertilizer dose as water soluble fertilizer through fertigation by micro sprinkler irrigation (T10) recorded the highest number of flower cushions per tree per season (377.6) as against 16.60% increase over the control (314.9) at 0.05% significance. The same treatment (T10) recorded the best in terms of other flowering characters viz., area of pollen grain (504.1 μm 2 ), equivalent diameter of the pollen grain (27.4 microns), radius of the pollen grain (13.3 microns), pollen output (34.9), pollen viability (89.2%), pollen germination (88.1%) as against 38.39, 23.72, 24.06, 28.65, 17.38 and 36.55% increase over the control (T1) respectively. Fertigation with 125% recommended fertilizer dose as water soluble fertilizer through fertigation by micro sprinkler irrigation recorded the maximum flowering characters.


INTRODUCTION
India offers considerable scope for cocoa cultivation, production and further development.Though cocoa has been known as the beverage crop even before tea and coffee, it is relatively a new crop to India.Cocoa readily responds to applied fertilizers to meet its nutrient requirements (Armando et al., 2001).Through fertigation methods, nutrients are added to the soil in adequate doses and interval through which qualitative improvement of produce can also be attained to a larger extent.In India, mostly the cocoa growing farmers are adopted surface irrigation with soil application of fertilizers.This will cause low productivity of less than 1 kg beans per tree per year.Production of quality beans in cocoa (single bean weight of more than 2 g) will enable the farmers to earn more income.
Being a shallow rooted crop, cocoa requires frequent doses of fertilizers coupled with soil moisture to utilize the *Corresponding author.E-mail:plantdoctorkrishna@gmail.com,Tel: +91 9659498935.Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License nutrients more effectively (Noordiana et al., 2007).
Fertigation ensures higher fertilizer use efficiency, besides providing scope for making soil amendments and even biological methods of plant protection (Oliveira et al., 2006).In the fertigation method, fertilizers can be applied throughout the crop growing season in phased manner, in various split doses, in any desired concentration.This is in contrast to the conventional practice where larger amounts of fertilizers are placed on the soil at the beginning of the season in one or very few split doses (Dangler and Locascio, 1990).
Considering the high yield potential in cocoa, nutrient application with due consideration on various crop growth stages viz., vegetative, flowering, pod set, pod development and maturity will help in realizing the potential yield (Krishnamoorthy and Rajamani, 2013).Flowering is cauliflorous and flowering cycle follows certain seasonal patterns.In India, it occurs from January to February with a peak in July to August.Flowering and fruit set are the most critical events occurring after establishment of a crop (Davenport and Nunez-Elisea, 1990).
Fertilization at proper time and proper dose will increase the pod yield (Patel and Rajput, 2000).Flowering in cocoa is determined by multi various factors like genetic factor, environmental factors, age of the tree, plant growth hormones, availability of soil moisture and nutrients as reported by Thondaiman (2011).Application of water soluble fertilizers through micro sprinkler fertigation registered better results in pollen parameters in mango (Davenport and Nunez-Elisea, 1990).Hence, the study was undertaken to evaluate the flowering characters and yield characters of cocoa using different fertigation schedules by drip and micro sprinkler irrigation.

MATERIALS AND METHODS
The geographical location of the experimental site is located at 10° 58' 0" N latitude, 76° 56' 0" E longitude and at an altitude of 258 m above MSL with aveage anual rain fall of 844 mm.Six year old cocoa trees were selected for the study.The varietal description of cocoa indicated that they were F1 seedling progenies (Forestero type), raised through seedlings (of F1's) supplied by Kerala Agricultural University, India.In coconut plantation of thirty year old with spacing of 8 x 8 m, the cocoa plants are intercropped with a spacing of 3 x 3 m (Figure 1).In case of drip irrigation, two emitters were installed with a discharging rate of 8 lph (litres per hour).Two micro sprinklers transmitting at 60 lph micro sprinkler -1 were installed to cover the entire basin.The micro sprinkler type is half sub circle with a height of 30 cm and it has sprinkling capacity of 60 cm area.The venturi was used for mixing of fertilizer with water.The study was laid out in randomized block design with thirteen treatment combinations (Table 1).The experiment having fertilizer application methods at two levels that is, drip and sprinkler and the fertilizer application rates at 3 levels that is, 75, 100 and 125%.
An annual application of 100 g N, 40 g P2O5 and 140 g K2O through the mode of surface irrigation (T1) is recommended for annual basis per tree in two splits (1 st dose in 1 st week of April and 2 nd dose in 1 st week of September).Surface irrigation was carried out once in seven day's interval.The fertilizers were applied through drip and micro sprinkler irrigation system (fertigation) at Krishnamoorthy et al. 267 weekly intervals for drip and micro sprinkler treatments (T2 to T13) and the irrigation was carried out once in a day (20 L tree -1 day -1 ).

Data collection
The observations on flowering characters were recorded as per standard procedures and analyzed statistically.Flowering in cocoa was throughout the year and two peak harvest seasons viz., March to May and September to November were observed.Among these two seasons, March-April (flowering) to July (pod harvest) season is considered as lean cropping period while September (flowering) to December (pod harvest) season is considered as peak cropping period.The geometry of the pollen grains was studied during 2010 and 2011.Pollens grains were collected from freshly dehisced anthers by gently tapping the anthers on glass slides which containing a drop of glycerol.Then cover slips were placed over the pollens and slides were observed under a microscope with the aid of ocular and stage micrometers (Mishra et al., 2006) connected with a computer in ordinary light.The observations were recorded from 50 pollen grains in each treatment and the data were analyzed in Q 500 MC WIN software programme.

RESULTS
In the present study, high variation was noticed in the number of flower cushions per tree and number of flowers per cushion with various fertigation treatments.4), radius of the pollen grain (13.3 and 13.3 µ) during first and second season of 2011.
The highest perimeter of the pollen grain was recorded in the treatment received 125% RDF as water soluble fertilizer through fertigation by micro sprinkler irrigation (98.9 µ) during first season in 2011 (Table 5).Duringsecond season, application of 100% RDF as water soluble fertilizer through fertigation by micro sprinkler irrigation registered highest pollen grain value (99.3 µ).Among the several treatments, the treatment which received 125% RDF as water soluble fertilizer through fertigation by micro sprinkler irrigation recorded more pollen output (34.9), pollen viability (89.2%) and pollen germination (88.1%) during 2011 (Table 6).

DISCUSSION
Among the different combinations, water soluble fertilizer with micro sprinkler irrigation showed better results.Application of 125 or 100% recommended NPK as water soluble fertilizer through micro sprinkler fertigation produced more number of flower cushions per tree and number of flowers per cushion.In general, the number of flower cushions per tree in the first year ( 2010) was lower as compared to second year (2011).The flower cushions in cocoa are spread over the trunk and main branches, the number is influenced more due to the soil nutrient; climatic conditions existed in the previous year.The fertigation treatments imposed in the first year would have influenced emergence of new flower cushions only in the second or later years.Because the trees perform better in second year with the increased flowering is in line with findings of Mongi-Zekri and Koo (2003).
The better photo-assimilates and hormonal balance would have improved the sink strength of trees treated with cent per cent RDF through micro sprinkler fertigation 5.1 5.2 5.2 5.0 5.0 5.0 5.1 T3 5.3 5.6 5. 5 5.4 5.5 5.5 5.5 T4 5.9 5.4 5.7 5.6 5.3 5.5 5.6 T5 4.9 5.1 5.0 5.2 4.9 5.1 5.0 T6 4.7 4.9 4.8 5.0 5.1 5.1 4.9 T7 5.1 5.0 5.1 4.9 5.0 4.9 5.0 T8 6.0 6.0 6.0 6.5 5.7 6.1 6.1 T9 7.4 6.9 7.2 7.0 6.8 6.9 7.0 T10 7.2 7.0 7.1 6.9 6.6 6.8 6.9 T11 5.4 6.1 5.8 6.4 6.3 6.4 6.1 T12 6.4 6.2 6.3 6.9 6.6 6.8 6.5 T13 6.1 5.8 5.9 6.6 6.4 6.5 (subjected to higher levels of available nutrients through fertigation) through acceleration of mega and microsporogenesis and differentiation of axillary buds into reproductive ones.Higher level of N, P and K resulted in rapid flower production than lower levels as reported by Takahashi et al. (1993).Application of water soluble fertilizers through micro sprinkler fertigation registered better results in pollen parameters like area, equivalent diameter, radius, perimeter, pollen output, pollen viability, pollen germination and pollen tube length.These might be due to enhanced level of auxinlike substances which would have been triggered by split application of WSF through micro sprinkler fertigation.High levels of auxin-like substances promote the flowering parameters either by nullifying the effect of GA 3 (or) by decreasing the permeability of cell membrane, particularly the plasmalemma (Eyheraguibel et al., 2008).Davis et al. (1991) also supported this by stating that aminosuccinamic acid (B 995) increases the membrane permeability of fruits.Many plant growth substances develop a strong physical association with lecithin and have direct influence on cell membrane functions towards reproductive parts growth as opined by Keith (2006).

Conclusion
Fertigation studies on cocoa through micro sprinkler irrigation with a dose of 100 or 125% RDF as water soluble fertilizer (WSF) has shown increase in flowering characters like number of flower cushions per tree (377.6), number of flowers per cushion (7.03), equivalent diameter of the

Figure 1 .
Figure 1.Lay out of drip and micro sprinkler in cocoa.

Table 1 .
Treatment details of the experiment.
RDF -Recommended dose of fertilizer, WSF -water soluble fertilizer.

Table 2 .
Effect of drip and micro sprinkler fertigation on number of flower cushions per tree at various seasons for two years.

Table 3 .
Effect of drip and micro sprinkler fertigation on number of flowers per cushion at various seasons for two years.

Table 4 .
Effect of drip and micro sprinkler fertigation on area and equivalent diameter of the pollen grain at various seasons.

Table 5 .
Effect of drip and micro sprinkler fertigation on radius and perimeter of the pollen grain at various seasons.

Table 6 .
Effect of drip and micro sprinkler fertigation on pollen output (numbers), pollen viability (%) and pollen germination (%) at various seasons.