I think, partial root drying....especially in perennial fruits

Scientia Horticulturae

Volume 117, Issue 1, 12 June 2008, Pages 15-20📷

Comparative effects of regulated deficit irrigation (RDI) and partial root-zone drying (PRD) on growth and cell wall peroxidase activity in tomato fruits,https://doi.org/10.1016/j.scienta.2008.03.009Get rights and content

Abstract: The effects of regulated deficit irrigation (RDI) and partial root-zone drying (PRD) on tomato fruit growth and cell wall peroxidase activity in tomato exocarp were investigated in growth chamber conditions. The RDI treatment was 50% of water given to fully irrigated (FI) plants and the PRD treatment was 50% of water of FI plants applied to one half of the root system while the other half dried down, with irrigation shifted when soil water content of the dry side decreased 15–20%. RDI significantly reduced fruit diameter, though PRD reduced fresh weight while having no significant effect on fruit diameter. The activity of peroxidase was significantly higher in RDI and PRD treated plants compared to those of FI. Differences between RDI and PRD were expressed on temporal basis. In the fruits of RDI treated plants peroxidase activity began to increase in the phase when fruit growth started to decline with the peak of enzyme activity of 6.1 HRPEU g−1 FW reached in the phase of mature green fruits when fruit growth rate was minimal. Increase of peroxidase activity in PRD fruits coincided with the ripening phase and the peak of enzyme activity (5.3 HRPEU g−1 FW) was measured at the end of fruit ripening. These data potentially identified contrasting and different roles of tomato exocarp cell wall peroxidase in RDI and PRD treated plants. In RDI treated plants peroxidase may have a role in restricting fruit growth rate, although the increase in enzyme activity during ripening of PRD treated fruit pointed out that peroxidase may also control fruit maturation by inducing more rapid process.

Effect of regulated deficit irrigation, partial root drying and N-fertilizer levels on sugar beet crop (Beta vulgaris L.), Agricultural Water Management,Volume 194, December 2017, Pages 13-23 .

Abstract: The study was conducted in the West of Iran, on the Karafs plain, in the Hamedan province in order to investigate the effects of water stress and nitrogen levels on quantitative and qualitative yields of sugar beet in a semiarid region with limited water resources. The experiments were carried out over two consecutive seasons in 2013 and 2014 respectively using split plots in randomized blocks with three replications. The main blocks included: Full irrigation (FI), three levels of partial root drying: 85 (PRD85), 75 (PRD75), 65 percent (PRD65) and regulated deficit irrigation at three levels: 85 (RDI85), 75 (RDI75) and 65 percent of the crop water requirement (RDI65). The sub blocks encompassed two levels of 100 (f100) and 75 percent (f75) of N-fertilizer requirements. Sugar beet of the Canaria variety was utilized in the study. The effect of the irrigation treatments was significant on all quantitative and qualitative characteristics of the sugar beet. By increasing the amount of irrigation water, root and white sugar yields increased and sugar content decreased. The highest root and white sugar yields obtained were through FI treatment with a mean root and white sugar yields of 54,235 and 7803 kg ha−1, respectively; however, its difference with PRD85 treatment yield was non-significant (with a mean root and white sugar yields of 51,113 and 7644 kg ha−1, respectively). The effect of fertilizer treatments on sugar content, white sugar content and all of the quantitative attributes of sugar beet were significant. With the increase in the application of N-fertilizer, root and white sugar yields increased and sugar content decreased. Therefore, under such experimental conditions, applying the PRD85treatment is recommended to prevent yield loss while saving 15% of irrigation water. Whatsmore, the study showed that among the various fertilizer treatments applied in the study, f100 treatment shows the best results.

Would you please study the following manuscript published by FAO:

http://www.fao.org/docrep/004/Y3655E/y3655e11.htm

Regulated deficit irrigation and partial rootzone drying have great potential to contribute to an increasingly water-efficient horticulture. PRD is better because deficit irrigation where deeper uppermost wet/dry zones are spatially separated and PRD timings are flexible.

https://www.wineaustralia.com/getmedia/50a58da5-ecc5-4aa1-ad06-8e3c87e38de9/NPI-01-01-RECV-27-10-03-PRD-irrigation-insights

The probable reasons are: 1. The plant has to use extra energy in the form metabolites to transfer the water, nutrients and aminoacids to the economic parts (grain, fruit etc.) in the optimum quantity which would ultimately results in bold seed/fruit production.

Article Effect of PRD Irrigation Method and Potassium Fertilizer App...