Increasing the effective use of water in green asparagus through deficit irrigation strategies

A six-year study was carried out to assess the effects of deficit (DI) and regulated deficit irrigation (RDI) strategies on yield and water use efficiency of two hybrids of asparagus (Asparagus officinalis L., hybrids Grande and Italo), in a typical semi-arid Mediterranean environment of Southern Italy. The experimental setup consisted of full irrigation (IRR; restoration of 100% of the crop evapotranspiration ETC), DI (restoration of 50% of ET, from the first fern flush until the end of the growing season) and two RDI (1: no irrigation supply from the first fern flush, crop development stage more sensitive to water stress, until end of the growing season, RDI1; 2: no irrigation supply from the second fern flush until the end of the growing season, RDI2) treatments. The relationships between yield and water regimes in the multi-year dataset were analyzed using linear mixed effect models (LMM) taking into account residual autocorrelation and comparing different variance-covariance structures. Irrigation treatments affected significantly the asparagus productivity. The six-year average yield was highest under IRR treatment (6.4 t ha(-1)) and lowest under RDI1 treatment (4.4 t ha(-1)) In comparison with IRR treatment, DI reduced ETC by 20% and yield by 13% (6-season average). Six-year average yields were similar in DI and RDI2 treatments (5.6 and 5.4 t ha(-1), respectively). Asparagus yield varied with hybrid. Italo hybrid showed higher yield performances (5.6 t ha(-1)) respect to Grande (5.3 t ha(-1)). The soil water deficit tolerance, assessed through the yield response factor (Ky of the marketable yield), was 0.61 and this value indicates that asparagus is mildly negatively affected by sub-optimal irrigation regimes. On the contrary, irrigation water use efficiency (WUE1) was clearly affected by the experimental treatment. WUE1 was higher (2.8 kg m(-3)) if asparagus experiences the soil water shortage during the first fern flush (RDI1). Operatively, full irrigation maximizes asparagus marketable yield, while reduced irrigation volume (DI or RDI2 treatments) seems a promising strategy, since it allowed reducing on average the irrigation volume supplies by 34% with asparagus marketable yield loss by 13%.