Decreased foliar nitrogen and crop yield in organic rainfed almond trees during transition from reduced tillage to no-tillage in a dryland farming system

• Tillage practices strongly affected plant nutrition in a short-term period.
• Transition from reduced to no-tillage decrease nitrogen status and almond crop production.
• Almond tree productivity is strongly co-limiting by nutrients in normal or wet years.
• δ15N was a good indicator of fertility in dryland agroecosystems.

Sustainable farming practices can be beneficial or detrimental to crop production in the short-term, which will strongly determine their appeal to farmers. We evaluated the effects of several sustainable practices on soil properties, plant nutrition and ecophysiology and crop yield in a semiarid agroecosystem. A three-year randomised experiment was conducted in a rainfed almond grove where the initial soil management was reduced tillage. Two alternative treatments were evaluated: reduced tillage plus green manure and no-tillage. The following soil and plant parameters were measured once per year: soil organic carbon, total nitrogen and Polsen; foliar N, P, δ13C and δ15N and crop yield. We found that soil bulk density increased significantly with no-tillage. Leaf δ15N was positively associated with soil fertility, foliar nutrient concentrations and crop yield across treatments. Leaf δ13C, Nfoliar and crop yield were strongly positively associated across treatments in every year of the study. Reduced tillage treatments displayed higher leaf δ15N, δ13C, Nfoliar and crop yield than the no-tillage treatment, indicating a sharp decrease in the leaf nitrogen status and intrinsic water use efficiency of almond trees during the transition from reduced tillage to no-tillage. In semiarid agroecosystems where soils are prone to compaction, some tillage is required to maintain optimal crop production in rainfed almonds.