Yield determination in olive hedgerow orchards. II. Analysis of radiation and fruiting profiles

Abstract

Profiles of fruit density, fruit size, and oil content were measured on 12 occasions in 7 olive orchards in Spain and 2 in Australia. Orchard structure varied widely. Height ranged from 2.0 to 5.5 m, row spacing from 3 to 6 m, and canopy width from 0.7 to 3 m. Most orchards were oriented north-south (N-S) but one in Spain was oriented close to east-west (E-W) (208 NE-SW). All orchards in Spain were cv. Arbequina, and in Australia they were cvv. Barnea and Picual. Analyses with a model of interception and transmission that estimated interception by individual sides of hedgerows revealed that fruit size and oil content were strongly related to intercepted radiation during the month before harvest across all orchards. Relationships were also evident between fruit density and interception but varied among orchards and years, indicating the importance of other environmental and probably physiological effects. In N-S orchards of cv. Arbequina, average fruit size and oil content increased linearly from 0.40 g (dry weight) to 0.72 g, and from 36 to 49% (of dry weight), as daily intercepted PAR increased from 6 to 25 mol/m 2 (15-60% of horizontally incident radiation). The general principles of response extended to E-W orchards. There, it was shown that generally large fruit with high oil content on S sides was consistent with the plateau responses to radiation evident in the more extensive N-S data. On the N side, however, and accounting for transmission through the hedgerow, both fruit size and oil content were greater than in positions intercepting equivalent radiation in N-S orchards. Examples are provided of the utility of responses of fruit density, size, and oil content in establishing combinations of row height, row width, and row distance to improve or maintain productivity in some of the orchards included in the study.

Effect of row spacing on vegetative structure, fruit characteristics and oil productivity of N–S and E–W oriented olive hedgerows

“…In E-W hedgerows, the differences between S and N sides were more evident in the most closely spaced rows. This response can be attributed to reduced transmission of radiation from sunlit S to shaded N sides as row spacing decreases even if, as previously suggested (Connor et al, 2009), lower threshold values of irradiance for fruit formation and development in olive, might increase productivity on the N side of closely spaced E-W hedgerows.…”

“…This response is consistent with greater irradiance on S sides in more widely spaced hedgerows and greater transmission through to N sides with consequently more even distribution of irradiance within both sides of widely spaced E-W hedgerows, depending upon porosity. Fruit oil content was similar between S and N sides at each height in all row spacings, a likely explanation being that oil accumulation occurs mainly in autumn when transmission from illuminated S to shadowed N side increases (Connor et al, 2009).…”

Simulation of oil productivity and quality of N–S oriented olive hedgerow orchards in response to structure and interception of radiation

“…• Orchards are oriented N-S, because previous work has shown that the relationships are not applicable to asymmetrically illuminated E-W orchards (Connor et al, 2009). …”

“…This is a reasonable assumption for N-S canopies of 0.7-m width or more, even those with a horizontal porosity of 15-20%. This arises because the trajectory of sunlight through the hedgerows is sufficiently long for almost complete interception diurnally (Connor et al, 2009). Further, since N-S hedgerows are illuminated equally on each side during the day, radiation passing through to the other side of the hedgerow before noon is compensated, on a daily basis, by complementary interception afterwards.…”

“…This combines two approaches First is a simulation study that establishes profiles of shortwave irradiance on canopy walls in response to orchard structure, location (latitude), and time of year (Connor, 2006). The model was previously verified during an annual cycle on hedgerows 2.0-2.5 m deep, 0.7-1.0 m wide at 4-m row spacing (Connor et al, 2009). Simulation of profiles of incident radiation on canopy walls is a straightforward geometrical problem that provides accurate predictions, as shown by comparison with measured data, in this and other studies on hedgerow crops (Jackson and Palmer, 1980;Oyarzun et al, 2007;Palmer, 1989).…”