Modelling soil tillage and mulching effects on soil water dynamics in raised-bed vegetable rotations

Reduced tillage and mulching may bring about new production systems that combine better soil structure with greater water use efficiency for vegetable crops grown in raised bed systems. These are especially relevant under conditions of high rainfall variability, limited access to irrigation and high soil erosion risk. Here we evaluate a novel combination of empirical models on water interception and infiltration, with a soil-water balance model to evaluate water dynamics in raised bed systems on fine Uruguayan soils to analyze the effect of reduced tillage, cover crops and organic matter addition on soil physical properties and water balance. In the experiment mulching increased water capture by 9.5% and reduced runoff by 37%, on average, leading to less erosion risk and greater plant available water over four years of trial. Using these data we calibrated and evaluated different models that predicted interception + infiltration efficiently (EF = 0.93 to 0.95), with a root mean squared error (RMSE) from 0.32 to 0.40 mm, for an average observed interception + infiltration of 28.8 mm per day per rainfall event. Combining the best model with a soil water balance resulted in predictions of total soil water content to 1 m depth (SWC_T) with RMSE ranging from 4.5 to 10.3 mm for observed SWC_T ranging from 180.4 to 380.6 mm. Running the model for a four-year crop sequence under 10 years of Uruguayan historical weather revealed that reduced tillage required on average 141 mm yr⁻¹ less irrigation water than conventional tillage combined with organic matter application, thus enabling a potential increase in irrigated area of vegetable crops and crop yields. Results also showed the importance of inter-annual rainfall variability, which caused up to 3-fold differences in irrigation requirements. The model is easily adaptable to other soil and weather conditions.     

Sample size for estimation of the plastochron in pigeonpea

The objectives of this study were to estimate the plastochron in pigeonpea (Cajanus cajan (L.) Millsp.) during the period between emergence and flowering using three methods of calculating the average daily air temperature and to determine the sample size (number of plants) needed to estimate the plastochron. A uniformity test (blank experiment) was conducted in an area of 1440 m² containing a pigeonpea crop. The area was divided into 360 plots of 2 m × 2 m, and 1 plant per plot was marked at random. In each of these 360 plants, the number of nodes on the main stem was counted at 37, 43, 50, 57, 64, 71, 78, 85, 93, 99, 106, 114 and 120 days after emergence (DAE). The average daily air temperature (T_average) was calculated using three methods: method 1: T_average = (T_minimum + T_maximum)/2; method 2: T_average = (T_0 h + T_1 h + T_2 h + ⋯ + T_23 h)/24; and method 3: T_average = (T_minimum + T_maximum + T_9 h + 2T_21 h)/5. For the three methods, the daily and cumulative thermal times were calculated from the date of emergence to early flowering and fitted to a linear regression of the average number of nodes on the main stem as a function of the accumulated thermal time. The plastochron was then calculated under each method as the inverse of the slope of the linear regression, and the required sample size (number of plants) to estimate the plastochron was determined by resampling with replacement. Plastochron values determined from the average daily air temperature calculated based on the three methods are different, and the use of the arithmetic mean of the hourly temperatures (method 2) should be favoured. Under method 2, the plastochron for pigeonpea was determined to be 21.34 °C day node⁻¹. To estimate the plastochron with 95% confidence interval amplitudes equal to 1, 2 and 3 °C day node⁻¹, it was necessary to count the number of nodes in 194, 50 and 24 pigeonpea plants, respectively.     

Carbon isotope discrimination and water use efficiency relationships of alfalfa genotypes under irrigated and rain-fed organic farming

Carbon isotope discrimination (Δ) has been proposed as a method for evaluating water use efficiency (WUE) in C₃ plants and as a precise technique for screening plants with higer tolerance under water deficit conditions. In this research, 18 alfalfa genotypes from different geographical origins were evaluated under irrigated and rain-fed conditions in organically managed fields in Austria. Significant differences were found amongst harvests for Δ-shoot under both conditions while genotype by harvest interaction was only significant under irrigated condition. Drought stress under rain-fed condition reduced the overall mean of water use efficiency and carbon isotope discrimination responses(up to 34%), but the ratios of reduction differed for characters and genotypes. Narrow ranges were found for all traits especially for WUE-TBY (total biomass yield) (0.78 kg m⁻³) and Δ-shoot (0.53‰) based on genotype means over locations and years, although variation and ranges were higher under irrigated condition. Regarding the variable and low correlations, simultaneous assessment of genotypes for Δ-shoot and biomass production can ensure the selection of superior genotypes and minimize potential biomass reductions that may result from using Δ-shoot as the only selection criterion to improve WUE. Sitel was the most water use efficient genotype(2.79 and 4.48 kg m⁻³ based on shoot dry matter and total biomass,respectively) across two condition (widely adapted genotype) followed by Mohajeran, Fix232 and Verko under irrigated condition (as specific adapted genotypes) and Vlasta, Sanditi, Ghara-aghaj under rain-fed condition.     

A comparison of cardinal temperatures estimated by linear and nonlinear models for germination and bulb growth of forage brassicas

Forage brassicas are widely used as a supplementary feed in temperate pasture systems but there is a lack of quantitative data about their growth and development. Furthermore, numerous models are available to estimate cardinal temperatures but there is uncertainty about whether linear or nonlinear models should be used. Initially a germination experiment was used to describe the rate response of nine forage brassicas to temperature. Three models were compared to estimate cardinal temperatures and the two best models were used for thermal time (Tt) accumulation for three groups of forage brassicas. Cardinal temperatures, defined as the base (T_b), optimum (T_opt) and maximum (T_m), differed among groups of species for the bilinear and Lactin models but were similar within a group of species for these models. In most cases, cardinal temperatures estimated by the bilinear and Lactin models for the B. rapa group ranged from 3 to 4 °C for T_b, 31 °C for T_opt and 41 to 48 °C for T_m. For the B. napus and B. napus biennis groups these temperatures ranged from 0 to 3 °C for T_b, 29 to 33 °C for T_opt and 38 °C for T_m. The B. oleracea group had temperatures from 0 to 1 °C for T_b, 25 to 27 °C for T_opt and 35 °C for T_m. A second data set based on hypocotyl thickening was used to estimate the base temperature (T_b) for bulb growth of turnips and swedes. Both models estimated an average T_b of 4.2 °C for bulb turnips and an average of 3.7 °C for swedes. The Lactin model was considered the most adequate model to describe temperature responses where as, in some cases, the bilinear model had to be modified to account for changes in the rate of development. More importantly, an appropriate range of test temperatures was crucial for the estimation of reliable cardinal temperatures, independent of the model used.     

Cassava yield loss in farmer fields was mainly caused by low soil fertility and suboptimal management practices in two provinces of the Democratic Republic of Congo

A better understanding of the factors that contribute to low cassava yields in farmers’ fields is required to guide the formulation of cassava intensification programs. Using a boundary line approach, we analysed the contribution of soil fertility, pest and disease infestation and farmers’ cultivation practices to the cassava yield gap in Kongo Central (KC) and Tshopo (TSH) provinces of the Democratic Republic of Congo. Data were obtained by monitoring 42 and 37 farmer-managed cassava fields during two cropping cycles in KC and one cropping cycle in TSH, respectively. Each field was visited three times over the cassava growing period for the observations. Logistic model was fitted against the observed maximum cassava root yields and used to calculate the achievable yield per field and for individual factor. At field level, the factor that led to the lowest achievable yield (Y_up(i)1) was considered as the dominant yield constraint. Cassava yield loss per field was expressed as the increase in the maximal root yield observed per province (Y_att- attainable yield) compared to Y_up(i)1. Y_att was 21 and 24 t ha⁻¹ in TSH and KC, respectively. With the cassava varieties that farmers are growing in the study areas, pests and diseases played a sparse role in the yield losses. Cassava mosaic was the only visible disease we observed and it was the dominant yield constraint in 3% and 12% of the fields in KC and TSH, respectively. The frequent yield constraints were suboptimal field management and low soil fertility. Cultivation practices and soil parameters led to Y_up(i)1 in 47% and 50% of the fields in KC, and in 47% and 41% of those in TSH, respectively. Individual soil parameters were the yield constraint in few fields, suggesting that large-scale programs in terms of lime application or recommendation of the blanket fertilisers would result in sparse efficacy. In KC, yield losses caused by low soil fertility averaged 6.2 t ha⁻¹ and were higher than those caused by suboptimal field management (5.5 t ha⁻¹); almost nil for cassava mosaic disease (CMD). In TSH, yield losses caused by low soil fertility (4.5 t ha⁻¹) were lower than those caused by suboptimal field management (6.5 t ha⁻¹) and CMD (6.1 t ha⁻¹). Irrespective of the constraint type, yield loss per field was up to 48% and 64% of the Y_att in KC and TSH, respectively. Scenario analysis indicated that the yield losses would remain at about two third of these levels while the dominant constraint was only overcome. We concluded that integrated and site-specific management practices are needed to close the cassava yield gap and maximize the efficacy of cassava intensification programs.     

Yield,water use and radiation use efficiencies of kenaf (Hibiscus cannabinus L.) under reduced water and nitrogen soil availability in a semi-arid Mediterranean area

Kenaf is a warm-season species that recently has been proved to be a good source of biomass for cellulose pulp for the paper industry in Mediterranean countries, where the use of hemp is problematic for legal reasons. A two-year research program aiming at studying the effects of different water regimes and nitrogen fertilization levels, upon plant growth, leaf area index, biomass accumulation, water and radiation use efficiency, was carried out on kenaf under a typically semi-arid Mediterranean climate of South Italy. In cv. Tainung 2, four different water regimes (I₀ = no irrigation, I₂₅, I₅₀ and I₁₀₀ = 25, 50 and 100% ETc restoration, respectively) and three nitrogen levels (N₀ = no nitrogen, N₇₅ and N₁₅₀ = 75 and 150 kg ha⁻¹ of N, respectively) were studied. The amount of water applied strongly affected plant growth (in terms of LAI, plant height and biomass) and final total and stem dry yield, which significantly increased from I₀ to I₁₀₀. Nitrogen did not exert any beneficial effect upon dry yield. Radiation Use Efficiency (RUE), calculated in the second year only, was the highest (1.95 g DM MJ⁻¹) in fully irrigated treatment (I₁₀₀) and the lowest (0.86 g DM MJ⁻¹) in the dry control.Water use efficiency (WUE) was rather similar among water regimes, whilst irrigation water use efficiency (IWUE) progressively increased with the decrease of total volume of water distributed to the crop by irrigation, from 3.47 to 12.45 kg m⁻³ in 2004 and from 4.27 to 7.72 kg m⁻³ in 2005. The results obtained from this research demonstrate that in semi-arid areas of South Italy, irrigation at a reduced rate (50% ETc restoration) may be advantageous, since it allowed a 42–45% irrigation water saving, when compared to the fully irrigation treatment, against a 23% (in 2004) and 36% (in 2005) yield reduction, and a still good efficiency (near that potential) in transforming the solar radiation in dry biomass was maintained (RUE = 1.76 g DM MJ⁻¹, against 1.95 g DM MJ⁻¹ in fully irrigated treatment).     

Effect of sustained deficit irrigation on physicochemical properties,bioactive compounds and postharvest life of pomegranate fruit (cv. ‘Mollar de Elche’)

In this study, the influence of sustained deficit irrigation (SDI; 32% of reference evapotranspiration (ET₀)) on physicochemical and sensory quality and bioactive compounds of pomegranates stored for 30, 60 and 90 days in air at 5 °C + 4 days at 15 °C, at each storage period, was studied and compared to a control (100% ET₀). Fruit from SDI had higher peel redness and greater firmness, soluble solids contents, vitamin C (27%), phloretin (98%) and protocatechuic acid (10%) levels, and total antioxidant capacity (TAC) (46%) than the control. Cold storage and shelf-life did not induce significant changes in soluble solids, pH, titratable acidity, and chroma and Hue. SDI fruit had retarded development of chilling injury (CI) symptoms, which appeared after 60 days of storage in comparison to 30 days in the controls. Anthocyanins, catechin, phloretin and protocatechuic, caffeic, p-coumaric and caffeic acids contents had greater increases in SDI fruit than in controls throughout the postharvest life. TAC was significantly (P < 0.05) correlated to anthocyanins, gallic acid and total vitamin C contents. Generally, after long term storage, the fruit grown under SDI showed higher sensory and nutritional quality, more health attributes and a longer shelf-life (up to 90 days at 5 °C + 4 at 15 °C) than fruit irrigated at 100% ET₀.     

The components of lucerne (Medicago sativa) leaf area index respond to temperature and photoperiod in a temperate environment

Irrigated crops of ‘Grasslands Kaituna’ lucerne were grown for 5 years in a temperate climate at Lincoln University, Canterbury, New Zealand (43°38′S, 172°28′E). From these the response of the components of leaf area index (LAI) to environmental factors was determined. A broken stick temperature threshold with a base temperature (T_b) of 1 °C at air temperatures (T_a) <15 °C and a T_b = 5 °C for T_a ≥ 15 was required to accumulate thermal time (Tt). Using this, the appearance of nodes on the main-stem (phyllochron) was constant in Tt within a re-growth cycle (30–42 days). The phyllochron was 37 ± 7 °Cd but declined from 60 to 37 °Cd as photoperiod decreased from 15.7 to 11.4 h. Branching began at the appearance of the fifth main-stem node with 2.5 secondary nodes produced per main-stem node in spring re-growth cycles but only 1.7 produced in summer. Leaf senescence increased from 0.3 to 1.08 leaves per main-stem node after the appearance of the ninth node. Spring re-growth cycles had a mean individual leaf area of 170 mm² compared with 400 mm² for summer re-growth cycles. These results demonstrate systematic variation in LAI components and suggest they need to be considered separately in response to environmental factors to provide a quantitative framework for crop simulation analyses of lucerne canopy development.     

Pod and seed numbers as a function of photothermal quotient during the seed set period of field pea (Pisum sativum) crops

The effects of radiation and temperature during the seed set period (SSP) on pod number per square metre (PN m⁻²) and seed number per square metre (SN m⁻²) and those of temperature during grain filling on unit seed weight (USW, milligram per seed) of field pea (Pisum sativum L.) were examined in experiments involving irrigated crops of three or more cultivars of contrasting maturity sown on two or more dates per year from 1996 to 1998 at Buenos Aires, Argentina. The duration of the seed-setting phase was estimated from records of the progress of flowering on the main stem and an estimate (obtained using an optimisation procedure) of the thermal time from flowering at which the uppermost reproductive node reached the final stage of seed abortion (FSSA). The FSSA at a particular node was assumed to be achieved 200 °C day (T_b=4 °C) after flowering at the same node. The grain-filling phase was assumed to run from the achievement of FSSA at the first reproductive node through to 200 °C day (T_b=0 °C) after the date of achievement of the FSSA by the second flowering node.The treatments (cultivar, sowing date, year) produced important ranges of above-ground biomass (AGB) at maturity (271–782 g m⁻²), seed yield (SY, 119–331 g m⁻²), SN (1062–3698 seeds m⁻²) and USW (67–150 mg seed⁻¹). Seed yield was strongly correlated with SN, and there was full compensation between SN and USW in large-seeded cultivars in the high SN range, but not at lower values of SN or in small-seeded cultivars. Both PN (r=0.83) and SN (r=0.87, P<0.0005) were strongly correlated with the mean daily value of the photothermal quotient (PQ=incident radiation/(mean temperature − base temperature)) for the seed-setting phase. Large- and small-seeded cultivars had PN/PQ and SN/PQ relationships with slopes which did not differ among categories but with significantly different intercepts. When the effects of low temperatures during flowering and early grain growth were allowed for, outliers on the PN/PQ and SN/PQ relationships for unstressed crops fell within the confidence limits of the respective linear regressions. Unit seed weight showed a negative response to mean temperature during the grain-filling phase in large- and small-seeded cultivars. We conclude that the relationships established in these experiments, taken together with previous work by other authors, constitute a robust basis for modelling the yield of unstressed field pea crops.     

Differential effect of regulated deficit irrigation on growth and photosynthesis in young peach trees intercropped with grass

The effects of a moderate soil water deficit on several shoot growth variables (1st and 2nd order shoot growth and final leaves number, final height and final number of 2nd order shoots) and on net photosynthesis were studied in young peach trees during the two years following plantation (January 2014). Trees were either fully irrigated (C), subjected to moderate water deficit (RDI) or subjected to moderate water deficit and associated with a grass-legume mixture on the entire orchard floor (RDI +G). Irrigation was scheduled according to soil water potential target ranges in order to keep C trees above −0.02 MPa, i.e. at field capacity, and RDI and RDI + G trees between −0.04 MPa and −0.06 MPa. The level of water deficit obtained was moderate but yet significantly reduced by 50% overall tree growth in 2014 in RDI. This reduction was enhanced when water deficit lasted longer and when it was associated with grass in RDI + G. No reduction in growth variables occurred in RDI in 2015 due to the shorter duration of water deficit. Overall reduction was observed in 2015 in RDI + G mostly due to a carry-over effect of the previous year. Net photosynthesis was reduced by the longer and more intense water deficit in 2014, but was not reduced during the soil water deficit in 2015. An indicator of plant process sensitivity to water deficit, taking into account the variable reduction with regards to the control, the water deficit intensity and its duration was used to classify shoot growth variables and net photosynthesis according to their sensitivity to water deficit. Variables could be classified according to the following order of ascending sensitivity: net photosynthesis <1st order final leaf number < final tree height <1st order final shoot length <2nd order final leaf number <2nd order final shoot number <2nd order final shoot length. Applying a moderate water deficit combined with full grass cover drastically reduces overall tree size due to grass competition.     

Quantifying growth and development of bulb turnips

Bulb brassicas are used as supplementary feed in intensive pastures systems. However, there is a lack of quantitative data to define their growth and development. This has limited the creation and use of prediction models and decision support systems. Thus a field experiment measured growth and development of ‘Barkant’ and ‘Green Globe’ turnips sown on five dates from November 2008 to March 2009. In a second field experiment ‘Green Globe’ turnips were sown on four dates from December 2009 to March 2010, under two ground cover treatments that changed mean soil temperature by ∼2 °C. Bulb initiation was defined botanically as when the hypocotyl was 10 mm thick, at 360 °Cd (±13.0) for ‘Barkant’ and 420 °Cd (±13.7) (T_b = 3.6 °C) for ‘Green Globe’. However, the bulb participation in dry matter production occurs after an 18 mm hypocotyl thickness, which occurred at ∼500 °Cd for both turnip cultivars. A single base parameter of 0.995 described the exponential decline of the leaf:bulb ratio. Relationships also described how leaf production and total leaf area expansion changed up until bulb initiation. Radiation use efficiency (RUE) ranged from 1.13 to 1.33 g DM/MJ total. A constant rate of total leaf area expansion (0.015 m²/m²/°Cd) was obtained up to LAI_c for ‘Green Globe’ turnips. A third pot experiment confirmed the thermal time requirement to bulb initiation based on direct assessment of the hypocotyl thickening of ‘Barkant’ and ‘Green Globe’ turnips. Temperature was shown as the main driver of bulb development and growth. The relationships provided could be used to improve the performance of prediction models.     

Energy of biomass sorghum irrigated with reclaimed wastewaters

The sustainability of biomass sorghum (Sorghum bicolor L. Moench) in the Mediterranean environments is linked to the potential to increasing the crop productivity using irrigation water of different qualities: fresh and wastewater. An experiment was conducted in Southern Italy during 2012 and 2013 growing seasons to determine the biomass production and to estimate the yielded energy from sorghum irrigated with fresh water and municipal wastewaters. Two stages of wastewater reclamation process were compared: tertiary and secondary treatments.During the growing seasons, the crop growth (biomass and LAI) was surveyed on sorghum crops irrigated with three water qualities. In order to determine the effects of the irrigation water qualities on the final energy yielded, on the harvested biomass, structural components (cellulose, hemicellulose and lignin contents for deriving the ethanol production) and high heating value were analyzed. The data obtained during two crop seasons showed that, sorghum irrigated with municipal wastewater plant produced more dry biomass (23.3 vs 20.3 t ha⁻¹), energy yield (383 vs 335 GJ ha⁻¹), and ethanol (6824 vs 6092 L ha⁻¹) than sorghum biomass with fresh water. As a consequence, the water efficiency for producing bioenergy increased when the waste waters were supplied in substitution of fresh waters. Different indices were calculated for comparing the effect of the water quality on the water use efficiency (WUE) of biomass sorghum crops.     

Treatment with chlorine dioxide extends the vase life of selected cut flowers

The accumulation of bacteria in vase water is often associated with premature senescence in many cut flower species. In the present study, we tested the efficacy of aqueous chlorine dioxide (ClO₂) to extend flower display life by preventing the build-up of bacteria in vase solutions. The addition of 2 or 10 μL L⁻¹ ClO₂ to clean deionized water extended the vase life of Alstroemeria peruviana ‘Senna’, Antirrhinum majus ‘Potomic Pink’, Dianthus caryophyllus ‘Pasha’, Gerbera jamesonii ‘Monarch’, Gypsophila paniculata ‘Crystal’ and ‘Perfecta’, Lilium asiaticum ‘Vermeer’, Matthiola incana ‘Ruby Red’ and Rosa hybrida ‘Charlotte’ flowers by 0.9–13.4 d (7–77%) relative to control (i.e. 0 μL L⁻¹ ClO₂) stems. The beneficial effects of ClO₂ treatment were associated with a reduction in the accumulation of aerobic bacteria in vase water and on cut surfaces of flower stems. ClO₂ treatment was also effective in maintaining or extending the vase life of A. majus ‘Potomic Pink’, Dendrathema × grandiflorum ‘Albatron’, G. paniculata ‘Perfecta’ and M. incana ‘Ruby Red’ flowers even when stems were placed into water containing 10¹¹ CFU L⁻¹ bacteria. The efficacy of 10 μL L⁻¹ ClO₂ in vase water containing 0.2 g L⁻¹ citric acid and 10 g L⁻¹ sucrose to extend the display life of G. jamesonii ‘Lorca’ and ‘Vilassar’ flowers was equal to or greater than other tested biocides (i.e. aluminum sulfate, dichloroisocyanuric acid, 8-hydroxyquinoline sulfate, Physan 20™, sodium hypochlorite). Taken collectively, the results of the present study highlight the potential of aqueous ClO₂ for use as an alternative antibacterial agent in flower vase solutions.     

Effects of water supply methods and seed moisture content on germination of China aster (Callistephus chinensis) and tomato (Lycopersicon esculentun Mill.) seeds

Uniform and fast germinating seeds are of prime importance for agriculture. To improve the germination properties of seeds, different treatments called priming are used. These methods generally involve the controlled uptake of water by the seeds. To be able to understand the processes involved in different priming methods the aim of the research was to study the relationship between the methods of water supply, water uptake rate by seeds, seeds moisture content and germination of China aster ‘Jolanta’ and tomato ‘Janosik’ seeds. Seeds of these species were primed by: (i) soaking in excessive amount of distilled water for 0–1440 min in the ratio of seeds to water (v:v) of 1:3; (ii) soaking in limited amount of distilled water 10–1280 ml kg⁻¹of seeds; (iii) matriconditioning in the ratios of 1:0.4:0.2–2.0 (w:w:w) for seeds, Calflo and water, respectively. The imbibed seeds were incubated for 1 day at 20 °C and seed moisture content was measured after incubation. Additionally, in seeds moistened up to 37% (China aster) and 35% (tomato), dynamics of water uptake were examined. Seeds, after imbibition and incubation, were dried to the initial moisture content (m.c.). Percentage of the germinated seeds, maximum germination (G_max), time for the first seed to germinate (T₁), time to reach 50% germination (T₅₀), time between 10 and 90% of G_max (T₉₀–T₁₀), at 5, 20 or 35 °C for the China aster seeds and at 15, 20 or 35 °C for tomato were evaluated.The results showed that water supply methods significantly affected seed imbibition rates and dynamics of seed germination, although these depended on plant species. It was found that water uptake was fastest in seeds soaked in excessive water amount and also that China aster took water faster than tomato. Imbibition of seeds during matriconditioning in Calfo and in limited water amounts was slower. Imbibition of seeds up to 37% m.c. for China aster and 35% m.c. for tomato, irrespective of the conditioning method, was the most favorable for germination. The earliest germination was observed in seeds soaked in excessive amount of water and incubated for 1 day. Germination of seeds matriconditioned, and those conditioned in limited water amount for 1 day was slower. We conclude that although the optimal final moisture content is independent of the different water supply methods used, the water supply method itself strongly affect the germination properties (T₁, T₅₀ and T₉₀–T₁₀ dynamics of germination).     

Strategies to optimize nitrogen efficiency when fertilizing with pig slurries in dryland agricultural systems

In dryland agricultural systems, pig slurry (PS) is usually applied to cereal crops only at sowing, and slurries accumulate for the rest of the year in pits. In this context, a four-year experiment was established in order to evaluate the feasibility of PS applications at the barley or wheat tillering stage. The main treatments were PS either applied at sowing (25 Mg ha⁻¹) or not, but they alternated after a two-year period. Both were annually combined with eight side-dressing treatments at cereal tillering: mineral N as NH₄NO₃ (M; 60 or 120 kg N ha⁻¹ yr⁻¹), PS from fattening pigs (PSf; 17, 30, 54 Mg ha⁻¹ yr⁻¹), PS from sows (PSs; 25, 45, 81 Mg ha⁻¹ yr⁻¹) and a treatment without N. The combined fertilization treatments were 18 plus a control (no N applied). In the context of crop rotation, the biennial alternation of PS applied at sowing allowed the control of soil nitrate increments, while PS side-dressing improved N recovery compared with a unique application at sowing. The highest yields (>3.6 Mg ha⁻¹ yr⁻¹) were obtained with an annual average (4-yr) N rate close to 173 kg N ha⁻¹ (±40 kg N ha⁻¹). The best overall strategies corresponded to PSs side-dressings of 50–90 kg N ha⁻¹. These PSs rates also recorded the highest values on the five calculated N-efficiency indexes, which were higher than or similar to results from M side-dressings or those recorded in the literature. These similarities (M vs. PSs) were also shown by the reduction of unaccounted-for N inside the overall N balance. Thus, split PS application during the crop cycle is a sound fertilization option in dryland systems.     

Effect of cyclic exposure to ozone gas on physicochemical,sensorial and microbial quality of whole and sliced tomatoes

The effect of a humidified flow of ozone-enriched air applied cyclically (4 ± 0.5 μL L⁻¹ of O₃ for 30 min every 3 h) on metabolic behaviour and sensorial and microbial quality of whole and fresh-cut ‘Thomas’ tomatoes stored up to 15 days at 5 °C was examined. The application of O₃ initially stimulated the respiration rate in a way similar to a stress, although after 2 days, the metabolic activity decreased to a rate lower than that of control (air flow). In O₃-treated whole and sliced tomatoes a higher sugar (fructose and glucose) and organic acid (ascorbic and fumaric) content was found. The kind of cut (whole or slices) did not affect the sensitivity of tomato to O₃. In whole tomatoes, O₃ maintained the tissue firmer than in control fruit while no influence was found on slices. The O₃ treated fruit retained a good appearance and overall quality in slices but experienced a reduced aroma. Also, O₃ substantially reduced microbial counts, being more noticeable on bacteria (1.1–1.2 log₁₀ units) than on fungi (0.5 log₁₀ units). This effect was higher when the storage time was longer and when a higher O₃ level (7 μL L⁻¹) was used. O₃ did not cause any damage or off-flavour in slices or whole tomatoes. In conclusion, the assayed O₃ treatment can be useful for maintaining quality and reducing microbial populations in whole and sliced tomato.     

Old tall durum wheat cultivars are suited for dual-purpose utilization

The lateness, tallness and high vigour of old tall durum wheat cultivars could be advantageous for dual-purpose use and their high propensity for lodging should be reduced by grazing. A 3-year field trial was performed in Sardinia, Italy, in a typical Mediterranean environment. Crops of the durum wheat cultivar Senatore Cappelli were sown in October, and grazing was simulated by clipping half of the plots at the terminal spikelet stage of development. The forage biomass derived from clipping varied greatly between seasons (from 0.8 to 3.3 t ha⁻¹ dry matter) in response to the notable inter-seasonal variability in weather conditions. Cultivar Senatore Cappelli showed good recovery following clipping, with the ability to attain almost complete radiation interception well before anthesis. The high number of leaves that emerged after clipping might have contributed to this good recovery. Nevertheless, clipping reduced the dry matter produced by anthesis (16 t ha⁻¹ in clipped compared to 21 t ha⁻¹ in unclipped crops) as well as the final dry matter (DM_MAT) (19 t ha⁻¹ in clipped compared to 23 t ha⁻¹ in unclipped crops), although these differences disappeared when the clipped biomass was included. The lower lodging observed at anthesis in the clipped (21%) compared with unclipped crops (63%) likely reduced the difference between treatments. The lower DM_MAT of clipped treatments was reflected in a lower grain yield (GY) (3.4 t ha⁻¹ vs 4.2 t ha⁻¹ in the unclipped treatment). Clipping did not affect the amount of nitrogen present in the biomass, nitrogen uptake efficiency or radiation use efficiency. GY reduction after clipping was mediated by the reduction in spikes m⁻² and kernels m⁻² (KNO). Spike fertility was not affected by clipping, because the same amount of radiation was available for each spike (about 1 MJ). The period with reduced ground cover after clipping was reflected in an increased evaporation and reduced transpiration, which did not alter the total water used and increased the transpiration efficiency in terms of DM_MAT.Old tall durum wheat cultivars manifested good suitability for dual-purpose use in environments with low attainable yields because their low grain yield potential contributed to reducing the negative effects of clipping on GY. Their high straw yield and kernel protein percentage represented an advantage with respect to semi-dwarf cultivars.     

Low temperature phosphine fumigation for postharvest control of Liriomyza huidobrensis Blanchard (Diptera: Agromyzidae) on carnation

Phosphine (PH₃) fumigation with different concentrations and exposure durations at low temperature was studied to determine its effects on Liriomyza huidobrensis Blanchard (Diptera: Agromyzidae) on carnations, and on postharvest quality. Laboratory tests showed that tolerance of L. huidobrensis to phosphine fumigation at 5 °C varied with different life stages. 1 d-old eggs and adults showed the highest susceptibility, and 3 d-old eggs was the most tolerant stage. In the fumigation tests of 3 d-old eggs with a range of phosphine concentrations from 0.46 to 2.73 mg L⁻¹ and exposure durations from 6 to 144 h at 5 °C, 85.96–282.08 h fumigation durations were required to achieve 99% mortality with different phosphine concentrations. The expression of C^0.77T = k was obtained, which indicated that exposure duration other than phosphine concentration was the critical factor in the toxicity of phosphine against the 3 d-old eggs of L. huidobrensis. Controlled atmosphere (CA) treatment with increased CO₂ and reduced O₂ had synergistic effects on phosphine toxicity. Phosphine fumigation could achieve 100% mortality for insects of L. huidobrensis on carnation, and had no significant adverse effects on vase life and damage indices of carnation at 1.92 mg L⁻¹ PH₃ and 8% CO₂ for 32 h, and at 3.44 mg L⁻¹ for 3 d at 5 °C. All results suggested that phosphine fumigation at low temperature could be used as an alternative for postharvest control of L. huidobrensis on carnations.     

A dynamic model of potential growth of olive (Olea europaea L.) orchards

A model of potential olive oil production is presented, based on a three-dimensional model of canopy photosynthesis and respiration and dynamic distribution of assimilates among organs. The model is used to analyse the effects of planting density (high and super-high density orchards with 408 and 1667 trees ha⁻¹, respectively) and climate change (ΔT of 4 °C and CO₂ concentration of 740 ppm) on olive oil production. To evaluate its predictive power, the simulations were tested with published measurements of leaf area, growth and yield for a high density olive orchard cv. ‘Arbequina’ in Cordoba, Spain. The model slightly overestimated (less than 7%) the different measurements reported in the experiment. For all simulations, the maximum yields obtained were in agreement with literature. Simulations showed that climate change had a very small effect on yields due to compensation of the negative and positive effects of temperature and CO₂ on photosynthesis and respiration. However, high temperatures led to some sterile years due to lack of vernalization. The model predicts that super-high density olive orchards achieve higher potential yields than high-density systems and that maximum yields are reached on the third year of the orchard. The advantage of a higher density is a higher interception of solar radiation, especially during the first years of the orchard. In all the simulations, the model predicted a small decrease of the radiation use efficiency for oil production with the age of the orchard as well as an important inter-annual variability (range of 0.11–0.19 g (MJ PAR)⁻¹), indicating that the use of a constant radiation use efficiency may not be adequate to predict oil production.