Interaction of fertigation and water management on apple tree productivity, orchard nutrient status, and fruit quality

Intensive methods of orchard cultivation require more effective ways of irriga-tion and fertilization. Recently apple (Malus ×domestica) orchards in the Trentino area of northeastern Italy have converted from traditional sprinkler irrigation to drip irrigation, both with or without fertigation. An experimental field trial was started at the end of 2008 in a ‘Golden Delicious’/M9 orchard at Tres (Province of Trento) to develop specific fertilization plans, in order to limit fertilizer input and reduce nutrient runoff into waterways. A factorial experiment with two fertilizer treatments (soil application of granular fertilizers or fertigation through drip emitters) and two water application rates (1500 or 3000 m3/ha/yr) was established. Compared with granular fertilizer, fertigation significantly increased leaf greenness, increased leaf nitrogen (N) concentration, and reduced phosphorus (P) concentration in the fruits at harvest. The Normalized Difference Vegetation Index (NDVI) values, a measure of canopy growth, were affected by both fertilization and water rate. Fertigation, through the end of July, enhanced NDVI values compared to granular fertilization, while NDVI values during the growing season had variable responses to water application rate. Application of the higher water rate decreased sugar and firmness values of fruits. The reduced water application rate decreased the concentrations of N, boron (B), and calcium (Ca) in the fruits, and increased fruit magnesium (Mg) concentration. The results of this three-year Trentino apple trial suggest a generally positive effect of fertigation on enhanced effectiveness of fertilization and improved fruit quality. Further research on the interaction of fertilizer and water management is required to fully develop the scientific basis for fertigation recommendations for local growers