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Drought sensitivity in olive trees varies throughout the season. The yield response to drought needs to consider the final use of the fruits and harvest date. In Mediterranean climates, the oil accumulation tends to occur in a period of low evaporative demand and during the rainy period. The aim of this work was to evaluate the effect of water stress during pit hardening on the yield components of oil olive trees. The experiment was conducted during three seasons (2017–2019) in a mature hedgerow olive orchard (11 years-old, Arbequina cv). The experiment design was a randomized completed block with 4 repetitions of 4 different irrigation treatments. Treatments were: Control, no water stress throughout the season; Regulated deficit irrigation (RDI)-1, moderate water stress during pit hardening and total recovery after the last week of August; RDI-2, same as RDI-1 but with severe water stress and partial recovery; and sustained deficit irrigation (SDI), constant applied water rate and the same seasonal water than RDI-2. The irrigation scheduling in RDIs were based on the frequencies of the trunk growth rate. No significant differences were found in fruit and oil yield between treatments. There were a significant relationship between water status measurements and fruit and oil yield. Part of the decrease in fruit yield with midday stem water potential (SWP) was related to fruit moisture, as no significant fruit drop was found. Only conditions of water stress in 2017, before the end of endocarp size, were related to a great reduction of fruit volume and, consequently, with fruit and oil yield. The relationship between the percentage of oil in dry weight and SWP was quadratic in different phases. Such relationships could help quantify the water stress level in these periods to maximize oil accumulation. © 2021 Elsevier B.V.

Overcoming the consequences of future scarcity of P is crucial to ensure agriculture sustainability. This requires decision-making processes depending on data on the P status of agricultural fields, commonly conducted with soil P tests (SPTs), and efficient use of the resource on a societal scale following a circular economy approach. All this will decrease the P losses and the subsequent environmental impact. However, SPTs are not universal and, even for a given SPT, the definition of threshold values for fertilizer response is not accurate. This work aimed to define models to predict Olsen P threshold values, allowing the identification of P-responsive sites at the European scale as a basis for more accurate and sustainable P fertilization schemes based on a circular economy approach. To this end, a data set was compiled based on a literature review that describes the Olsen P threshold values for different crops under field conditions. Subsequently, an analysis of potential P fertilizer requirements was performed on agricultural soils of the European Union (EU) using the data set of the LUCAS project and how this need can be covered with a circular economy approach. Environmental factors were more relevant than crops to explain the variation in threshold values. A regression model involving soil pH and clay content and annual average rainfall as independent variables explained 61% of the variance in Olsen P threshold values. When soil pH and clay content were the only explanatory variables, the explained variance was 49%. This reveals the need to take into account factors related to P buffer and sorption capacity to estimate accurate threshold values. We detected that only 27.8% of EU cropland soils and 42.7% of grassland soils were P-responsive. We can conclude that a more precise allocation of the resource is possible in Presponsive sites and also that most of the European demand for P could be covered by recycling P from manure, wastewater, and municipal solid

Although complexation with soil organic matter may improve zinc (Zn) bioavailability to plants, the effect of Zn sorbent surface on the use of complexed Zn by plants remains unknown. The objective of this research was to elucidate how Zn complexation with humic substances (HS) and phytate affects the uptake of Zn by wheat plants depending on the main sorbent surface in growth media, i.e., carbonates and Fe oxides. To this end, two pot experiments were performed, one using Fe oxide-coated siliceous as the siliceous growth medium sand and the other using a mixture of calcareous sand and siliceous sand as the calcareous growth medium. Each experiment involved three Zn sources, Zn-HS complex, Zn phytate, and ZnSO4. All sources were applied with surface irrigation at two Zn rates (0.25 and 2 mg kg−1 growth medium). The Zn-HS complex significantly increased Zn uptake by plants in both media, relative to the other two Zn sources, but no significant difference was observed between Zn phytate and ZnSO4. In the calcareous medium, Zn-HS complex and Zn phytate resulted in significantly higher dry biomass yields of wheat than ZnSO4. In the siliceous medium, spike and shoot dry biomass yields with Zn-HS complex at the low rate and Zn phytate at both rates were not significantly different from those with ZnSO4 at the high rate. After harvest, approximately 50% of the Zn applied as Zn-HS complex remained extractable by diethylenetriaminepentaacetic acid (DTPA), while this proportion was less than 20% for the other Zn sources. Thus, Zn-HS complex and Zn phytate are sources of available Zn for plants, and they are more effective than ZnSO4 in increasing plant growth, particularly when carbonates are the main Zn sorbent surface.

Drought sensitivity in olive trees varies throughout the season. The yield response to drought needs to consider the final use of the fruits and harvest date. In Mediterranean climates, the oil accumulation tends to occur in a period of low evaporative demand and during the rainy period. The aim of this work was to evaluate the effect of water stress during pit hardening on the yield components of oil olive trees. The experiment was conducted during three seasons (2017–2019) in a mature hedgerow olive orchard (11 years-old, Arbequina cv). The experiment design was a randomized completed block with 4 repetitions of 4 different irrigation treatments. Treatments were: Control, no water stress throughout the season; Regulated deficit irrigation (RDI)-1, moderate water stress during pit hardening and total recovery after the last week of August; RDI-2, same as RDI-1 but with severe water stress and partial recovery; and sustained deficit irrigation (SDI), constant applied water rate and the same seasonal water than RDI-2. The irrigation scheduling in RDIs were based on the frequencies of the trunk growth rate. No significant differences were found in fruit and oil yield between treatments. There were a significant relationship between water status measurements and fruit and oil yield. Part of the decrease in fruit yield with midday stem water potential (SWP) was related to fruit moisture, as no significant fruit drop was found. Only conditions of water stress in 2017, before the end of endocarp size, were related to a great reduction of fruit volume and, consequently, with fruit and oil yield. The relationship between the percentage of oil in dry weight and SWP was quadratic in different phases. Such relationships could help quantify the water stress level in these periods to maximize oil accumulation.

Soil fertility is typically assessed by chemical analysis, which is expensive and time-consuming, and hence impractical for site-specific fertilizer management. Visible and near infrared (Vis–NIR) spectroscopy has been used for determining soil properties and chemically extractable plant nutrients. However, the suitability of Vis–NIR for accurate assessment of nutrient availability to plants has not yet been fully explored. In this work, we examined the accuracy of this technique as a new nutrient availability index, and in the case of P as a proxy for plant-available P. To this end, total plant-available P in soil was quantified in a P-depletion experiment with crops, and the availability of Ca, Mg, K, and Fe was assessed by chemical extraction. Vis–NIR spectroscopy allowed us to accurately estimate plant-available P, which depends not only on soil factors but also on the crop performance to take up P. Vis–NIR spectroscopy proved effective in identifying P, Ca, Mg, K, and Fe responsive sites. Precise estimation of plant-available P was a result of accurately predicting soil properties governing P availability to plants by Vis–NIR spectroscopy. In addition, this technique provided accurate predictions of soil properties influencing the dynamics of applied P and K fertilizer, which can be useful to adapt fertilization practices to soil properties. Vis–NIR spectroscopy can therefore enable a qualitative leap to cost-effective integral assessment of soil fertility by providing accurate predictions of soil functioning rather than mere estimates of availability indices, thereby facilitating more sustainable use of resources in agriculture.