Effects of Olive Mill Wastewater on Soil Microarthropods and Soil Chemistry in Two Different Cultivation Scenarios in Israel and Palestinian Territories

Although olive mill wastewater (OMW) is often applied onto soil and is known to be phytotoxic, its impact on soil fauna is still unknown. The objective of this study was to investigate how OMW spreading in olive orchards affects Oribatida and Collembola communities, physicochemical soil properties and their interdependency. For this, we treated plots in two study sites (Gilat, Bait Reema) with OMW. Among others, the sites differed in irrigation practice, soil type and climate. We observed that soil acidity and water repellency developed to a lower extent in Gilat than in Bait Reema. This may be explained by irrigation-induced dilution and leaching of OMW compounds in Gilat. In Bait Reema, OMW application suppressed emergence of Oribatida and induced a community shift, but the abundance of Collembola increased in OMW and water-treated plots. In Gilat, Oribatida abundance increased after OMW application. The effects of OMW application on soil biota result from an interaction between stimulation of biological activity and suppression of sensitive species by toxic compounds. Environmental and management conditions are relevant for the degree and persistence of the effects. Moreover, this study underlines the need for detailed research on the ecotoxicological effects of OMW at different application rates

Fruit load governs transpiration of olive trees

We tested the hypothesis that whole-tree water consumption of olives (Olea europaea L.) is fruit load-dependent and investigated the driving physiological mechanisms. Fruit load was manipulated in mature olives grown in weighing-drainage lysimeters. Fruit was thinned or entirely removed from trees at three separate stages of growth: early, mid and late in the season. Tree-scale transpiration, calculated from lysimeter water balance, was found to be a function of fruit load, canopy size and weather conditions. Fruit removal caused an immediate decline in water consumption, measured as whole-plant transpiration normalized to tree size, which persisted until the end of the season. The later the execution of fruit removal, the greater was the response. The amount of water transpired by a fruit-loaded tree was found to be roughly 30% greater than that of an equivalent low- or nonyielding tree. The tree-scale response to fruit was reflected in stem water potential but was not mirrored in leaf-scale physiological measurements of stomatal conductance or photosynthesis. Trees with low or no fruit load had higher vegetative growth rates. However, no significant difference was observed in the overall aboveground dry biomass among groups, when fruit was included. This case, where carbon sources and sinks were both not limiting, suggests that the role of fruit on water consumption involves signaling and alterations in hydraulic properties of vascular tissues and tree organs.</p

Tef (Eragrostis tef) Responses to Phosphorus and Potassium Fertigation under Semi-Arid Mediterranean Climate

Tef (Eragrostis tef (Zucc.) Trotter) is an annual small grain, panicle bearing, C4 cereal crop native to Ethiopia, where it is a major staple food. The objectives of the present study were to characterize the responses of two tef genotypes to escalating phosphorus (P) and potassium (K) levels and to determine an optimum range for P and K at which tef performance is maximized. Two experiments were carried out in the Gilat Research Station, each testing two different genotypes of tef (405B and 406W), one experiment in pots in controlled conditions, and the other in the field. In both experiments, the highest grain yield increased until 6 mg L−1 P, and declined at 12 mg L−1 P. The decline was precipitous and significant in the pot experiment, and gradual and statistically insignificant in the field experiment. In the pots experiment, the grain yield increased until 40 mg L−1 K, with no significant decrease thereafter. The effect of K concentration was only seen in the grain yield and not in the size of the other plant organs. In the field experiment, grain yield was highest at 80 mg L−1 K, but it was not statistically different from 40 mg L−1. The effect of K on growth was only apparent at maturity and not at flowering

Long-Term Impact of Phosphorous Fertilization on Yield and Alternate Bearing in Intensive Irrigated Olive Cultivation

Phosphorus (P) availability significantly impacts olive tree reproductive development and consequential fruit production. However, the importance of P fertilization in olive cultivation is not clear, and P application is usually recommended only after P deficiency is identified. In order to determine the long-term impacts of continuous P fertilization in intensive irrigated olive cultivation, the growth and production of trees in an intensive orchard with or without P fertilization were evaluated over six consecutive seasons. Withholding of P resulted in significant reduction in soil P quantity and availability. Under lower P availability, long-term fruit production was significantly impaired due to reduced flowering and fruit set. In addition, trees under conditions of low P were characterized by higher alternate bearing fluctuations. Olive tree vegetative growth was hardly affected by P fertilizer level. The impairment of tree productivity was evident in spite of the fact that leaf P content in the treatment without P fertilization did not decrease below commonly reported and accepted thresholds for P deficiency. This implies that the leaf P content sufficiency threshold for intensive olive orchards should be reconsidered. The results demonstrate the negative impact of insufficient P fertilization and signify the need for routine P fertilization in intensive olive cultivation

Long-Term Impact of Potassium Fertilization on Soil and Productivity in Intensive Olive Cultivation

The olive growing sector is transitioning from traditional to intensive irrigated cultivation, dictating a need to reconsider orchard management practices including fertilization. Potassium (K) is an essential nutrient, typically found in high concentrations in plants. Orchard K fertilization requirements are commonly derived from the disparity between assumed tree requirements and extractable soil K. The long-term impact of insufficient fertilization on K available in the soil, growth, and yield of irrigated field-grown olive trees was evaluated over six consecutive seasons. Withholding of K fertilization led to lower exchangeable and soluble K concentrations in the soil and significantly impaired yield. The reduction in yield was attributed to reduced flowering and fruit set, resulting in a lower fruit number. Tree vegetative growth and flowering quality traits were not affected. In addition, trees not receiving K appeared to be more susceptible to alternate bearing. Following two seasons of omitting K fertilization, leaf K concentration did not decrease below the conventionally accepted sufficiency threshold for olive (0.8%). In spite of this, the trees produced significantly lower yields. Our results suggest that long-term insufficient K fertilization results in reduced soil available K and consequently impairs tree productivity. The results imply that the sufficiency threshold for K in diagnostic leaves should be reconsidered for intensive orchards. Moreover, the current method for K deficiency detection using leaf K concentration may be inadequate for intensive orchards. Integration of other parameters, such as fruit K content, leaf Na, and changes in soil exchangeable K content or sorption energy, may promote a more reliable analysis of orchard K nutritional status

Management of Verticillium Wilt of Avocado Using Tolerant Rootstocks

The global avocado industry is growing, and farmers are seeking to expand their plantations. However, many lands suitable for avocado planting were previously cultivated with hosts of the soil-borne fungal pathogen Verticillium dahliae, which is the causal agent of Verticillium wilt (VW). VW can seriously impair avocado orchards, and therefore, planting on infested soil is not recommended. The use of different rootstock types allows avocado cultivation in various regions with diverse biotic and abiotic constraints. Hence, we tested whether genetic variance among rootstocks may also be used to manage avocado VW. Six hundred trees, mostly Hass and some Ettinger, grafted on 23 selected rootstocks were evaluated for five years in a highly V. dahliae-inoculated plot for VW symptoms, fungal infection, and productivity. The selected rootstocks displayed a significant variation related to VW tolerance, and productive avocado rootstocks with potential VW tolerance were identified. Moreover, the rootstock productivity appears to correlate negatively to the susceptibility level. In conclusion, planting susceptible rootstocks (e.g., VC66, VC152, and VC26) in infested soil increases the likelihood of massive tree loss and low productivity. Whereas, tolerant rootstocks (e.g., VC804 and Dusa) may restrict VW and enable avocado cultivation on infested soils

Whole-tree water balance and indicators for short-term drought stress in non-bearing 'Barnea' olives

Drainage-weighing lysimeters allowed monitoring of water balance components of non-bearing olive (Olea europaea cv Barnea) trees over a 3-month period including short-term events of controlled but severe water stress. The objective of the study was to evaluate a variety of soil and plant-based water status and drought stress monitoring methods on the basis of tree-scale evapotranspiration (ET). As the trees entered into and recovered from water stress, meteorological data, actual ET (ETa), soil water content and changes in leaf turgor pressure were continuously monitored. Additionally, midday measurements of stem water potential, stomatal conductance, canopy temperature, and quantum yield of PSII photochemistry were conducted. Diurnal (dawn to dusk) measurements of all the above were made hourly on days of maximum stress. Shoot elongation rate was measured for periods of stress and recovery. Quantum yield of PSII photochemistry, stomatal conductance, and stem water potential all successfully indicated reductions in whole-tree water consumption beginning at moderate stress levels. These measured parameters fully recovered to the levels of non-stressed trees soon after water application was renewed. Shoot elongation was reduced 25-30% for the 10-day period during and following drought and recovered thereafter to levels of non-stressed trees. Whole-tree ETa was reduced by as much as 20% even following full recovery of the leaf level parameters, suggesting reduced canopy size and growth due to the stress period. Non-destructive, continuous (turgor pressure) and remotely sensed (canopy temperature) methods showed promising potential for monitoring effects of water stress, in spite of technological and data interpretation challenges requiring further attention.Lysimeter Plant growth Transpiration Physiological monitoring Water status Olea europaea