Farm manure and bentonite clay amendments enhance the date palm morphology and yield

Abstract

Date palm production contributes significantly to socio-economic development and food security in the dryland areas of Southern Tunisia. Soil degradation and nutrient depletion have dramatically increased in recent years. This is leading to a decline in date palm yields in these oases-based production systems. Locally derived bentonite clay has been identified as a new soil amendment to improve date morphological characteristics and date production. In this study, a 3-year field experimental study was carried out on 3-year-old Deglet Nour date palms growing in sandy soil of a Tunisian oasis (Fatnassa, Southern Tunisia). The study’s aim was to compare the effect of two amendment types: (i) sand (S) mixed with farm manure (M) and bentonite clay (B) (=BSM) and (ii) sand mixed with farm manure (SM) on the soil characteristics and morphological features of date palm. The results indicated that soil macro- and micronutrient contents were enhanced under BSM. Soil water retention in BSM also increased to 290 ± 0.3 mm m−1 compared to 70 ± 0.2 and 50 ± 0.5 mm m−1 for an untreated (no amendment) and SM treatment, respectively. The amelioration of morphological characteristics was observed for the canopy diameter reaching 226 ± 0.6 cm in BSM treatment compared to 172 ± 0.6 cm in untreated palm trees. The height of the palms increased by 69 ± 0.8 cm from 29 ± 0.1cm in the control treatment, and leaf number increased from 40 leaves palm−1 in BS to 60 leaves palm−1 in BSM treatment. The leaf mineral content was significantly been improved in the third year, and the leaf NPK contents were 220 ± 0.6 mg kg−1, 17 ± 0.1 mg kg−1, and 200 ± 0.04 mg kg−1, respectively, in BSM treatments. The effect of the farm manure and bentonite clay was noticeable for the yield production, and the SM and BSM treatments offered yields of 70 ± 0.9 kg palm−1 and 80 ± 0.5 kg palm−1, respectively. It could partly ameliorate the alternate year bearing phenomenon of the Deglet Nour date variety. We conclude that the joint application of farm manure and bentonite clay does represent a viable option to further improve the production and resilience of date palms in dryland areas.