The objective of this experiment was to evaluate in the long-term (9 years), the suitability of compost as a fertilizer in commercial peach orchard. The experiment was carried out on nectarine trees (Prunus persica var. nectarina), Stark RedGold grafted on GF677 peach · almond (P. amygdalus L.) hybrid. The treatments were: (1) unfertilized control; (2) mineral fertilization including phosphorus (P at 100 kg ⁄ ha) and potassium (K at 200 kg ⁄ ha) applied at planting and nitrogen (N at 70-130 kg ⁄ ha ⁄ yr) split in two applications at 40 days after full bloom (60%) and in September (40%); (3) cow manure supplied at planting [10 t dry weight (dw) ⁄ ha] and then, from the forth year at the rate of 5 t dw ⁄ ha ⁄ yr in spring; (4) compost supplied at planting (10 t dw ⁄ ha) and then, from the forth year at the rate of 5 t dw ⁄ ha ⁄ yr in spring; (5) compost supply at a rate of 5 t dw ⁄ ha ⁄ yr, and (6) 10 t dw ⁄ ha ⁄ yr, both treatment 5 and 6 split as described for treatment 2. Nitrate-N soil concentration was usually not affected by treatments. Soil microbial carbon, organic matter, total N, P, K were increased by application of organic fertilizers. SOM and total N were positively correlated to soil microbial biomass. Aggregate stability, humic and fulvic acid concentration were not affected by fertilization treatment. Only the application of compost at 10 t dw ⁄ ha ⁄ yr (6) increased fruit production.
A better understanding of plant mechanisms in response to drought is a strong premise to achieving high yields while saving unnecessary water. This is especially true in the case of biomass crops for non-food uses (energy, fibre and forage), grown with limited water supply. In this frame, we investigated growth and physiological response of two genotypes of biomass sorghum (<em>Sorghum bicolor</em> (L.) Moench) to contrasting levels of soil moisture in a pot experiment carried out in a greenhouse. Two water regimes (high and low water, corresponding to 70% and 30% field capacity) were applied to JS-2002 and Trudan-8 sorghum genotypes, respectively bred for dry sub-tropical and mild temperate conditions. Two harvests were carried out at 73 and 105 days after seeding. Physiological traits (transpiration, photosynthesis and stomatal conductance) were assessed in four dates during growth. Leaf water potential, its components and relative water content were determined at the two harvests. Low watering curbed plant height and aboveground biomass to a similar extent (ca. 70%) in both genotypes. JS-2002 exhibited a higher proportion of belowground to aboveground biomass, <em>i.e</em>., a morphology better suited to withstand drought. Despite this, JS-2002 was more affected by low water in terms of physiology: during the growing season, the average ratio in transpiration, photosynthesis and stomatal conductance between droughty and well watered plants was, respectively, 0.82, 0.80 and 0.79 in JS-2002; 1.05, 1.08 and 1.03 in Trudan-8. Hence Trudan-8 evidenced a ca. 20% advantage in the three traits. In addition, Trudan-8 could better exploit abundant moisture (70% field capacity), increasing aboveground biomass and water use efficiency. In both genotypes, drought led to very low levels of leaf water potential and relative water content, still supporting photosynthesis. Hence, both morphological and physiological characteristics of sorghum were involved in plant adaptation to drought, in accordance with previous results. Conversely, the common assumption that genotypes best performing under wet conditions are less suited to face drought was contradicted by the results of the two genotypes in our experiment. This discloses a potential to be further exploited in programmes of biomass utilization for various end uses, although further evidence at greenhouse and field level is needed to corroborate this finding.
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