J.E. Cabanas

Olive Yields and Tree Nutritional Status during a Four-Year Period without Nitrogen and Boron Fertilization

Nitrogen (N) and boron (B) are mobile elements in soil. Therefore, the application of these nutrients is typically performed annually, as a single dose, or even split into several fractions in the case of N. In olive (Olea europaea L.), however, controversial literature has suggested that yearly application of N may not be required. In the case of B, some authors indicated that one single application is sufficient for 3 or 4 years. Thus, the effects of these elements on olive yield, leaf N and B concentrations, as well as soil available N and B were investigated during a field trial performed in an olive orchard located in northeast Portugal, in which N and B were not applied for four consecutive growing seasons. Fertilizer treatments consisted of the following: the control, which was a complete fertilization plan where N and B were included (N + B treatment); –N treatment, with N excluded from the fertilization plan; and –B treatment, with B excluded. Available soil N and B were estimated from a pot experiment with Italian ryegrass (Lolium multiflorum L.) and from chemical laboratory extractions. Olive yield decreased significantly in the –N treatment in comparison to the control. A slight yield reduction in the –B treatment in comparison to the control was also observed. Leaf N and B concentrations decreased significantly in the –N and –B treatments, respectively, in comparison to the N + B treatment. Soil available N and B at the end of the experiment were significantly lower in the –N and –B treatments, respectively, in comparison to the N + B control. The results showed a continuous decrease in olive yield and leaf N and B concentrations, which reflected the reduction in soil-available N and B in the treatments lacking the respective nutrient. Therefore, it seems prudent to recommend adjustments to the rates of N and B every year to prevent reduction in tree crop performance and improve nutrient-use efficiency.

Effect of Soil Management on Olive Yield and Nutritional Status of Trees in Rainfed Orchards

Studies on the effect of groundcover treatments on perennial tree crops have been common in recent decades. However, few have included leaf analysis as an aid to understand the effects of groundcover treatments on tree crop growth and yield, in particular in rainfed olive orchards. Field experiments took place in northeast Portugal, over the course of eight consecutive years, in two commercial orchards selected on the basis of their contrasting situation regarding the floor-management system before the trial started. An orchard located in Bragança, currently managed as a sheep-walk, received the following treatments: sheep-walk (SW), where the natural vegetation was managed with a flock of sheep; mechanical cultivation (MC), which consisted of two tillage trips per year in the spring; and glyphosate (Gly), where the herbicide was applied once during the first fortnight of April. Another orchard near Mirandela, currently managed by tillage, received the following treatments: mechanical cultivation (MC); glyphosate (Gly); and residual herbicide (RH), where an herbicide with a residual component was applied late in the winter. The trees that underwent Gly treatments produced the greatest tree crop growth and olive yield. The worst results were achieved with the SW and MC treatments in the Bragança and Mirandela experiments, respectively. Leaf nitrogen (N) and boron (B) concentrations were significantly higher and lower, respectively, in the treatments that caused the higher and lower olive yields in both experiments. In the Mirandela orchard, where the leaf potassium (K) concentrations were close to the lower limit of the adequate range, the leaf K levels followed the pattern registered for N and B. The results showed a strong link between tree crop nutritional status and tree crop growth and olive yield. The groundcover treatments that facilitate nutrient absorption by olive trees yielded more crops.

Comparative Boron Nutritional Diagnosis for Olive Based on July and January Leaf Samplings

In this work, diagnosis of boron (B) nutritional status based on leaf B concentrations was compared for the most common leaf-sampling times for olive trees, January and July. For this purpose, field experiments were conducted over 4 years (2003–2006) in two rainfed olive groves located in Mirandela and Bragança, northeastern Portugal. Leaf samples were collected in January and July and analyzed for B by standard procedures. Fruit harvest occurred in December of each year. The crops followed typical alternate fruiting cycles. During the 4 years of the study, mean olive yields in the Bragança orchard fluctuated, yielding 3.6, 28.1, 5.5, and 22.7 kg tree−1. Yield variation per individual tree was also great. In the Bragança orchard and in the 2004 harvest, yields ranged from 1.2 to 52.7 kg tree−1. Leaf B concentrations also varied greatly between individual trees. In the Bragança orchard in the July sampling of 2004, values for individual trees varied from 12.2 and 23.7 mg B kg−1. From a total of 16 scatterplots generated from the relationship between leaf B concentrations and olive yields, 10 significant linear relationships were established; six of them were related to July sampling dates and four were related to January dates. The number of significant linear relationships established between leaf B concentration and olive yield was used as a criterion of the accuracy of the B nutritional diagnosis, because this represented the lowest experimental variability. By using this criterion, the July sampling date proved as better for B nutritional diagnosis, although the difference from January sampling date was not sufficient to disregard this. Leaf B concentrations were consistently greater in July than in January. Averaged across the 4 years of the study in both orchards, the difference was 4.3 mg B kg−1. This difference should be taken into account in the interpretation of leaf analysis results when B levels are close to the deficient critical concentration.