Impact of organic manure on fruit set, fruit retention, yield, and nutritional status in pomegranate (Punica granatum L. "Wonderful") under water and mineral fertilization deficits

This research was conducted on mature pomegranate (Punica granatum L. "Wonderful") trees growing at a site located in North Coast, Matrouh Governorate, Egypt. The aim was to investigate the impacts of different irrigation regimes in combination with different fertilizer regimes on the fruit set, fruit retention, yield, and nutritional status of the trees. The experimental factors were arranged in a split-plot design, with four replicates per treatment combination. The results indicated that all of the characteristics measured, including leaves nutritional status, percentages of fruit set, fruit drop, fruit retention, fruit cracking, fruit sunburn, and marketable fruit, and yield were significantly affected by the interaction between the irrigation treatment which denoted by percentages of reference evapotranspiration (ETo) and fertilizer regime. The application of 75% mineral fertilizer + 25% organic manure under deficit irrigation of 80% ETo increased the yield by an average of 18.23% over the 2 years compared with 100% mineral fertilization under full irrigation, while 50% mineral fertilizer + 50% organic matter under 80% ETo gave the maximum percentage of marketable fruit (86.23% and 86.84% in 2018 and 2019, respectively). The maximum water use efficiency was obtained with the 80% ETo treatment combined with 75% mineral fertilizer + 25% organic manure in both seasons with values of 9.69 and 10.06 kg/m(3) applied water, respectively. These results demonstrate that under the field conditions at the experimental site, the fruit set and retention could be improved by applying a reduced amount of mineral fertilizer in combination with organic manure and less irrigation water.