Influence of fruit number on fruit weight and yield of kiwifruit

Kiwifruit crop loading relationships published for pergola-trained vines in Hawkes Bay are shown to hold over a wider climatic range, several seasons and for T-bar training systems. Absorption of solar radiation by the vertical foliage 'walls' on the T-bar would reduce differences in total energy absorption between T-bar and pergola systems and contribute to the fact that training system was not, in itself, a significant determinant of yield. Relationships between harvest yield (Y) and fruit number (N) m^-2 of orchard allocated per female vine, and mean fruit weight (μ) in g, can be described by: (1)Y=Y_max( N (N+K)). and (2)Y= Nμ 1000. where K is a constant equal to 95.25 fruit m^-2 of orchard and Y_max equals 13.48 kg m^-2. After accounting for male vines, the latter figure corresponds to a maximum possible yield of 126 tonnes ha^-1. Equation (1) expresses the potential productivity of kiwifruit, given currently available genetic material and good management. Combining eqns. (1) and (2) with a normal parameterisation of harvest fruit size distributions, allows returns from a range of crop loading regimes to be calculated directly. Using this approach, New Zealand grower returns (1986/1987 prices) are shown to be optimised for an average fruit weight of 90 g which corresponds to a crop load of approximately 50 fruit m^-2. This information can be used by growers to develop pruning and thinning strategies that maximise returns rather than yield and also by industry to set price schedules that encourage the production of fruit in the most marketable size ranges.