Organic fertilization leads to increased peach root production and lifespan

We evaluated the effects of mineral and organic fertilization on peach root dynamics 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 if organic fertilizers affected 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 fertilization was P (100 kg ha-1 yr-1) and K (200 kg ha-1 yr-1) applied only at planting and N (70-130 kg ha-1 yr-1) split in two applications at 40 days after full bloom (60%) and in September (40%) each year. The compost fertilization represented a yearly rate of 10 MT DW ha-1 which approximates (in kg ha-1 yr-1) 240 N, 100 P and 200 K, split similarly to that described for the mineral fertilization of N. 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 to 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). Root lifespan was longer in compost-treated trees than in mineral-fertilized or unfertilized trees (P<0.01). Root lifespan 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, 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.