n mango trees, floral morphogenesis is initiated during cool weather. Temperatures of about 15O C or lower induce floral development, whereas temperatures of about 20O C or higher promotes vegetative shoots (Wolstenholme and Hofmeyr, 1985; Shu and Sheen, 1987; Whiley et al., 1989; Nunez-Elisea and Davenport, 1991; Nunez-Elisea et al., 1993).
In the tropics, mango trees flower during cooler night temperatures around 10 – 12 O C and dry months, generally experiencing a period of drought (Singh, 1960; Van der Meulen et al., 1971; Chacko, 1986; Verheij, 1986; Beal and Newman, 1986; Whieley et al., 1989). Most of the researchers have shown that a degree of water stress during flower bud development is advantageous (Cull, 1989; Larson and Schaffer, 1989; Singh, 1967). Furthermore, it has been demonstrated that the floral stimulus originates from mature leaves in mango and young leaves inhibit the floral bud initiation (Kulkarni, 1988). Hence, young mango leaves are incapable of producing floral stimulus, since flowers are initiated on dormant vegetative shoots whose leaves are fully expanded, mature, dark green and lignified. Water stress in the tropics or in warm environments during flower bud development restricts the production of new leaves in mango and consequently increases the proportion of inductive mature leaves relative to young ones. It is therefore possible that under marginally inducing temperatures in the tropics, mango floral induction can occur after a period of plant water stress, when canopies consist mainly of mature, inductive leaves (Nunez-Elisea and Davenport, 1994).
Lu and Chacko (2000) showed that water stress for 5 weeks promoted earlier and more intense flowering in mango trees of both ‘Kensington’ and Írwin’ cultivars. Final fruit yield was also higher in water stressed trees. In field grown trees in Thailand, water stress increased the intensity of flowering in mangoes (Pongsomboon et al., 1991). In a three year Australian study on 15 year old ‘Kensington Pride’ mangoes (Bally et al., 2000), it was demonstrated that water stress following the maturation of the first summer shoot flush after harvest significantly increased the percentage of flowering terminals. The average yield over the three years of the trials for water stress treatment was slightly higher than well watered trees. However, the water stressed trees produced a significantly higher yield in 1995 than well watered trees. The 1995 year had a warmer floral bud development period than the other two years indicating water stress has more profound effect in a warmer than a cooler year. Similarly, in a South African study in mangoes (Mostert and Hoffman, 1998), showed that not irrigating or water stress during winter months, annual production increased by 9% and water use decreased by 20%. Mostert and Hoffman conducted this trial in a summer rainfall region of South Africa. The water stress, which was a period of no irrigation, was applied to coincide with flower bud development and extended from about the beginning of May to middle of August. Irrigation was started as soon as the flowers on the panicle started to open. Fruit yield of trees under water stress during flower bud development was higher in all six years compared with that of trees which were irrigated during this period. The average yield of water stressed mango trees was 30.5 t/ha as opposed to 27.8 t/ha from those not stressed. This increase in yield was a result of weaker vegetative flush during flowering in water stress trees. The well watered trees vigorous flush competing for the same reserves needed by the flowers and young fruits, which resulted in a depleted fruit set and yield. Water stress during flower bud development had virtually no effect on fruit size. The probable reason for this is that the applied water stress was stopped when the flowers on the panicle started to open thus fruits were developing under non-stress conditions.
It is necessary to maintain a good supply of soil moisture with the start of flowering until close to harvest. Mango trees that are watered when the soil had diminished to 20% of available soil moisture gave better growth of buds, number of flowers, fruit set, fruit size, yield and K, Ca, Mg, Fe and Mn content in the foliage than those watered at 40 or 60 % of available soil moisture depletion (Pina et al., 2000). It is customary for some growers in north Queensland to either stop or reduce rate of water applied to a mango orchard two to three weeks before harvest. This practice gives the right amount of fruit colour/blush to be acceptable in the market and also helps in increasing the Brix degree (OB) reflecting sweetness of the fruit.
Therefore, it could be concluded through the research citation mentioned in this document that pre-flowering water stress during winter months has been shown to greatly enhance the potential to increase yields in mango by increasing the number of terminal that flower. It appears that water stress strengthens the floral induction signal during the floral differentiation stage of bud development.
The severity of water stress at different phenological stages of mango has differential impact on its production and fruit quality. Effect of water stress on mango is most critical during flowering, fruit set and fruit development period. Both total yield and fruit number per tree are substantially decreased by water stress. Lack of irrigation during flowering, fruit set or at rapid increase in fruit size alone can reduce yields up to 50%. Hence, irrigation practices should match mangoes “crop water use” depending on its phenological stages (Table. 1).
Table. 1. Water requirement of mango with respect to its phenological stages in north Queensland.
What are the performance measuring units to determine water use efficiency
The performance indicator of water use efficiency (WUE) under “Best Irrigation Management Practice” is measured and expressed in terms of megalitres per hectare (Ml/ha), tonnes per hectare (t/ha) and tonnes per megalitres (t/Ml). These measures are used here to show results on mango crop water use and benchmarking guidelines on irrigation practices.
How to match mangoes watering needs
The crop water use for a mango depends on its phenological stage (Table. 1). In mangoes, the crop water use can be determined through the process of “benchmarking”.
What is “Benchmarking”?
Benchmarking is a process of learning from your own past performance and the performance of others in pursuit of continuous improvement. Two methods that can be used to identify and benchmark, best irrigation management practices in mangoes, on-farm investigations and an industry survey. Then, the results of both, the on-farm investigations and the survey are combined to determine and benchmark best irrigation practices.
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