No abstract

Precise phosphorus (P) application requires a mechanistic understanding of mineral effects on crops' biology and physiology. Photosynthates assimilation, metabolism, and transport require phosphorylation, and we postulated that P is critical for the bloom and fruit-set of almond trees that rely on stored carbohydrate reserves. Hence, we studied the growth-physiology and carbohydrate dynamics in two-year-old almond trees irrigated with P concentrations between 1 and 20 mg L -1. Almond trees attained maximal photosynthesis, transpiration, and growth by 6 mg P L -1 in irrigation. Nevertheless, almond trees continued to extract P in 10 and 15 mg P L -1 irrigations, which corresponded to bigger starch reserves and yields. We attributed the augmented productivity to increased fruit-set (59% between 6 and 15 mg L -1 P), caused by more frequent (29%) honeybee visits. High P improved pollinators' visitation by enabling almond trees to utilize more of their starch reserves for nectar secretion (which increased by ~140% between 6 and 15 mg P L -1). This work illuminates P fertilization's benefits to plant-pollinator mutualism, critical to almond productivity, and reveals novel indices for optimal P application in almond orchards.

Grafting of fresh cuttings using drought-susceptible and low-yielding clones as scions on drought-tolerant clones as rootstocks offers the possibility of raising composite plants with improved productivity and drought tolerance. Hence, the study was aimed to widen the choice of compatible composites and to delineate the underlying factors responsible for productivity and drought tolerance in grafted plants. One year-old composite plants of TRF-1, TRF-2 and UPASI-28 cleft-grafted on the rootstocks of UPASI-2, UPASI-9, ATK-1 and TRI-2025 were field planted along with their respective controls and evaluated. The results indicated that productivity and drought tolerance of scion clones varied significantly with the rootstocks used. Significant increases in yield and yield components were noted in the following graft combinations compared with their corresponding self-rooted scion clones: TRF-1 grafted on UPASI-9 and ATK-1, TRF-2 grafted on all four rootstocks, and UPASI-28 grafted on UPASI-9, TRI-2025 and UPASI-2. The findings clearly emphasize the scion–rootstock interaction as the critical determinant of productivity in grafted plants compared with vigour, drought tolerance and yield potential of scion and rootstock clones. Further, high-yielding capacity of grafts over the ungrafted scions and rootstocks was largely dependent on the yield potential of the scion clone and the degree of scion–rootstock compatibility. Higher field survival and enhanced yield observed during the drought period in the compatible grafts demonstrated their better drought tolerance compared with their respective self-rooted scions.

Mineral fertilization through irrigation (fertigation) could optimize resource allocation and eliminate wastes in agriculture. Nevertheless, the fertigation of almond plantations is currently inefficient (50% nitrogen (N) recovery by yields) due to the limited empirical data to support field applications. For precise fertigation in horticulture, we aimed to determine the trees’ actual mineral uptake. We hypothesized that the mineral requirements depend on physiological development and would vary during the growing season as phenology shifts. To investigate this, we tracked the water, N, phosphorus (P), and potassium (K) mass-balances of almond trees in 1 m3 lysimeters and monitored their physiological performances. By canopy coverage (leaf area index—LAI)) and radial stem growth, we determined that almond trees invest in biomass between April and July (northern hemisphere). Then, for August until November, the almond trees accumulated metabolites and minerals for the succeeding winter dormancy. Annually, almond trees can utilize major N applications (~180 kg h−1) in early summer for vegetative growth, extract P (~50 kg h−1) by mid-summer for metabolic translocations, and accumulate K (>250 kg h−1) in late summer, possibly for osmotic compensations. Converting these realizations for farm conditions requires the further characterization of the mineral availability at the root zone, and the nutritional status of trees, under various field fertigation applications.