Fertilization of temperate fruit trees, such as grapevine ( Vitis spp.), apple ( Malus domestica), and pear ( Pyrus communis) is an important tool to achive maximum yield and fruit quality. Fertilizers are provided when soil fertility does not allow trees to express their genetic potential, and time and rate of application should be scheduled to promote fruit quality. Grapevine berries, must and wine quality are affected principally by N, that regulate the synthesis of some important compounds, such as anthocyanins, which are responsible for coloring of the must and the wine. Fermenation of the must may stop in grapes with low concentration of N because N is requested in high amount by yeasts. An N excess may increase the pulp to peel ratio, diluting the concentration of anthocyanins and promoting the migration of anthocyanins from berries to the growing plant organs; a decrease of grape juice soluble solid concentration is also expected because of an increase in vegetative growth. Potassium is also important for wine quality contributing to adequate berry maturation, concentration of sugars, synthesis of phenols and the regulation of pH and acidity. In apple and pear, Ca and K are important for fruit quality and storage. Potassium is the most important component of fruit, however, any excess should be avoided and an adequate K:Ca balance should be achieved. Adequate concentration of Ca in the fruit prevents pre- and post-harvest fruit disorders and, at the same time, increases tolerance to pathogens. Although N promotes adequate growth soil N availability should be monitored to avoid excessive N uptake that may decrease fruit skin color and storability.

We evaluated the effects of mineral and organic fertilizers on peach root dynamics in the growing season from 2003 to 2006 in a nectarine (Prunus persica L.) orchard, planted in 2001 and located in the Po valley, northeastern Italy. Very few studies have conducted long-term investigations of root dynamics of fruit crops. Our main objective was to determine whether organic fertilizers affect root dynamics differently than mineral fertilizers. The experiment was a completely randomized block design with four replicates of three treatments: unfertilized, mineral fertilized and composted with municipal waste. Mineral fertilizers included P (100 kg ha⁻¹ year⁻¹) and K (200 kg ha⁻¹ year⁻¹) applied only at planting and N (70–130 kg ha⁻¹ year⁻¹) split into two applications, one at 40 days after full bloom (60%) and the other in September (40%) each year. The compost fertilization represented a yearly rate of 10 metric tons (t) dry weight ha⁻¹, which approximates (in kg ha⁻¹ year⁻¹) 240 N, 100 P and 200 K, split similarly to that described for the mineral fertilization of N. Both root growth and survival were evaluated at 20-day intervals during the growing season by the minirhizotron technique. Compost increased the production of new roots compared with the other treatments (P < 0.01). Roots were mainly produced at a depth of 41–80 cm and from March to May and in late summer. An analysis of covariance indicated no significant effect of soil nitrate on root production (P = 0.47). The root lifespan was longer in compost-treated trees than in mineral-fertilized or unfertilized trees (P < 0.01) and it was strongly affected by time of birth; roots born later in the summer lived longer than those born in the spring. Across years and treatments, the average root lifespan was positively correlated with soil nitrate (r = 0.60; P < 0.001). Variation in root lifespan with method of fertilization could be accounted for by variation in soil nitrate concentration as indicated by no effect of fertilizer treatment on root lifespan when soil nitrate was included as a covariate. These results reveal how shifting from mineral to organic fertilizers may shift both soil properties and nutrient availability, leading to changes in both root production and lifespan.