Low Irrigation Treatment Research Articles

Nursery cultural practices influence morphological and physiological aspen seedling traits: implications for post-fire restoration

Aspen forests are threatened by the impacts of a changing climate and are showing large-scale mortality with meager natural regeneration to restore these loses. Therefore, there is an increasing demand for high-quality aspen seedlings to assist with forest restoration efforts. Nursery cultural practices can be used to alter aspen seedling traits to improve adaptability to dry planting conditions. In this study, the effects of container size (SC10 and D30; 158 and 490 mL, respectively) and nursery irrigation treatment (high and low irrigation; 90% and 70% container capacity, respectively) on seedling growth and a suite of morphological and physiological traits were investigated. The combination of large container size and low irrigation treatment resulted in seedlings with lowest height-to-diameter ratio and specific leaf area, which are desired traits for seedling performance on dry sites. Additionally, seedlings exposed to low irrigation conditions at the nursery stage had a lower (more negative) osmotic potential at full turgor, suggesting a higher likelihood of drought tolerance. Overall results from this study provide insight into utilizing nursery cultural practices to produce seedlings with target characteristics that may ultimately lead to establishment on harsh, dry planting sites in large-scale reforestation projects.

Bottom-up population regulation of Orthotomicus erosus on irrigated and fertilized Pinus eldarica: A comprehensive field study

The Mediterranean pine engraver, Orthotomicus erosus (Wollaston), is a destructive pest that has caused a significant threat to planted pine forests worldwide through feeding on phloem, disrupting sap flow and transmitting phytopathogens. This study investigated the bottom-up effects of different irrigation and fertilization treatments on the mean numbers of O. erosus immature stages (egg, larva and pupa) and adults in the pine forest of western Tehran, Iran. A total of 72 Pinus eldarica Medw. trees were selected in Chitgar Forest Park. The experiment was arranged as a split plot in a randomized complete block design with three replications. The irrigation treatments included non-irrigation, low-irrigation (30 liters of water per month) and high-irrigation (30 liters of water per two weeks) were assigned to main plots. Moreover, fertilizers of nitrogen 100 kg/ha, superphosphate 100 kg/ha and potassium sulfate 65 kg/ha were applied in subplots. Then, the total number of O. erosus life stages was counted under the bark samples (two 10 × 10 cm bark samples) separated from the pine trees. Results showed that irrigation and fertilization significantly affected the mean number of O. erosus from egg to adult stages. Irrigation had a more pronounced effect on the pest population than fertilization. The highest number of different life stages occurred in non-irrigated pines regardless of fertilization. Moreover, fertilizer effects were influenced by irrigation, where high irrigation negatively affected superphosphate + potassium sulfate fertilized pines and significantly increased the mean numbers of different O. erosus life stages compared to low-irrigation treatment. The lowest mean number of egg (11.95 ± 0.17), larva (8.62 ± 0.21), pupa (10.38 ± 0.13) and adult (9.04 ± 0.23) per bark samples occurred in superphosphate + potassium sulfate at low-irrigation plots. Interestingly, nitrogen fertilization increased pest density compared to unfertilized trees. Furthermore, despite the low mean number of different O. erosus life stages in superphosphate + potassium sulfate treatments, the nitrogen combination increased the pest density in both low and high-irrigation plots. These findings highlighted the importance of considering the interaction between irrigation and fertilizer types in the integrated pest management program for O. erosus.

San Diego Thornmint (Acanthomintha ilicifolia) Populations Differ in Growth and Reproductive Responses to Differential Water Availability: Evidence from a Common Garden Experiment.

The responses of rare plants to environmental stressors will determine their potential to adapt to a rapidly changing climate. We used a common garden approach to evaluate how six populations of the annual San Diego thornmint (Acanthomintha ilicifolia Lamiaceae; listed as endangered in the state of California and as threatened by the US Fish and Wildlife Service) from across the species range respond in terms of growth (biomass, height, and width) and reproduction (seed production, floral production, and next generation seed viability) to experimental differences in water availability. We found a significant irrigation-by-population interaction on the aboveground growth, wherein the differences in the magnitude and direction of treatment did not correlate directly with climate variables in natural populations. With respect to reproduction, the low-irrigation treatment produced more seeds per plant, more reproductive individuals, and a larger proportion of viable seed in most, but not all, populations. The seed production and the effect of irrigation on seed production correlated positively with rainfall at wild source populations. These results suggest that Acanthomintha ilicifolia responds to water limitation by creating more and higher-quality seed, and that plants locally adapted to a higher annual rainfall show a greater plasticity to differences in water availability than plants adapted to a lower annual rainfall, a finding that can inform the in situ demographic management and ex situ collection strategy for Acanthomintha ilicifolia and other rare California annuals.

Responses of yield, quality and water use efficiency of potato grown under different drip irrigation and nitrogen levels

Proper irrigation and fertilization are essential for achieve high tuber yield and quality in potato production. However, the high cost of these inputs necessitate optimization of their use to improve both water use efficiency and crop productivity. This study aimed to investigate the impact of irrigation and nitrogen fertilization on potato yield, quality and water use efficiency. The research included different drip irrigation treatments (100%, 66%, and 33% of field capacity) and nitrogen levels: 0 (N0), 100 (N1), 200 (N2), 300 (N3), 400 (N4) and 500 (N5) kg N ha−1. The results indicated that potato yield and growth were more sensitive to irrigation treatment than nitrogen levels. Full irrigation with 300 kg N ha−1 produced the highest total tuber yield, while low irrigation treatments resulted in significantly lower yields. In contrast, the 66% field capacity irrigation treatment consistently had the highest water use efficiency in both years of the study. Furthermore, the study showed that the quality characteristics of the tubers were negatively impacted by full irrigation treatments compared to low irrigation. These findings suggest that with appropriate irrigation and nitrogen application, potatoes can be produced with acceptable yields while conserving water and minimizing nitrogen use. This research emphasizes the importance of optimizing inputs to improve water use efficiency and yield productivity while reducing water. As a result, obtaining useful information on crop management for farmers to make informed decisions may be possible by achieving optimal irrigation and nitrogen levels.

Assessment of Wheat Genotypes under Low Irrigation Conditions Using Agro-physiological Traits and Grain Quality in North Delta of Egypt

Water scarcity in Egypt and globally makes producing new varieties having high grain yield using less water requirements is an important goal for wheat breeders. The present research was conducted to assess the response of sixteen bread wheat genotypes under normal irrigation (five irrigations) and low irrigation (one irrigation, 25 days, after sowing irrigation.) during 2018/19 and 2020/21 seasons at the Experimental Farm of Sakha Agricultural Research Station, Egypt. A randomized complete block design with three replicates was used for each irrigation treatment separately. Results showed that the normal irrigation treatment had considerably higher mean values for all studied traits except, proline, malondialdehyde, activity of peroxidase and catalase enzymes,1000-kernel weight, protein content, wet and dry gluten which had significantly higher mean values under low irrigation treatment. Under low irrigation conditions, the four genotypes Sakha 95, Line 4, Line 8 and Misr 3 superior other genotypes in grain yield with insignificant difference among them. Sakha 95 and Line 8 had the highest chlorophyll a and b, proline content, chlorophyll florescence, activity of both catalase and peroxidase enzymes. While, Line 4 had the highest activity of catalase and peroxidase, heaviest 1000-kernel weight and high content of crude protein. In addition to Misr 3 recorded the best values of both wet and dry gluten. It could be recommended with cultivation Sakha 95 or Misr 3 to achieve high grain yield with less irrigation water. While Line 8 and Line 4 need more evaluation to use it in the regions which suffering from water shortage also it will be benefit for breeder to use these genotypes in wheat breeding program.

Measuring and modelling nitrate fluxes in a mature commercial apple orchard

Leaching of nitrogen from intensive agriculture to groundwater and waterways is a source of environmental harm. Nitrate leaching beneath a commercial 10-year-old ‘Galaxy’ apple orchard was investigated using a combined measurement and modelling approach. Measurement of sapflow, climate, soil moisture, deep drainage and nitrate leaching beneath the root zone were monitored for 30 months in order to parameterise and calibrate the Soil Plant Atmosphere System Model (SPASMO). Sap flow peaked at around 15 L tree−1 day−1 in late January with average sap flow for the 2013/14 season of 8.58, 6.39 and 6.47 L tree−1 day−1 for the high (4.0 L ha−1), medium (2.3 L ha−1) and low (1.6 L ha−1) irrigation treatments, respectively. Deep drainage and nitrate leaching were highly variable and did not appear to be influenced by irrigation rate. Over the 30-month monitoring period, drainage beneath the rootzone averaged 89 mm yr−1, whilst nitrate leaching averaged 33.2 kg-NO3 ha−1 yr−1, equivalent to 55% of the applied fertilizer. Average nitrate concentration in the leachate exceeded the World Health Organisation threshold for drinking water of 50 mg L−1 in 41 out of 279 samples. Long-term modelling indicated the average amount of drainage and nitrate leaching were 136 mm yr−1 and 11.4 kg-NO3 ha−1 yr−1, respectively. Scenario analysis indicated that few options existed to reduce nitrate leaching at the site through irrigation and fertigation management.

The Effect of Irrigation Treatment on the Growth of Lavender Species in an Extensive Green Roof System

In green roofs, the use of plant species that withstand dry arid environmental conditions and have reduced water requirements is recommended. The current study presents the effect of irrigation amount on the growth of four different species of lavender; Lavandula angustifolia, Lavandula dentata var. candicans, Lavandula dentata var. dentata, and Lavandula stoechas established on an extensive green roof system and used in urban agriculture. Two irrigation treatments (high and low) determined by the substrate hydraulic properties were applied. Plant growth studied at regular intervals included measurements of plant height, shoot canopy diameter, plant growth index, shoot dry weight and stomatal conductance. The results were consistent and showed that low irrigation reduced plant growth. With the exception of L. stoechas, the appearance of plants watered with the low irrigation treatment was satisfactory, and their use under low water amount irrigation is supported. Interspecies differences among lavender species were present in both irrigation treatments. Overall, L. dentata var. candicans showed the greatest growth, followed in descending order by L. dentata var. dentata and L. angustifolia. In parallel, for stomatal conductance, L. dentata var. candicans showed the lowest value, similar to L. dentata var. dentata, and L. angustifolia the largest. Differences in plant characteristics and size among the latter three species can be considered in the design of extensive green roof systems. The use of substrate hydraulic properties was shown to be important for irrigation management on extensive green roof systems.

Climate and water availability impacts on early growth and growth efficiency of Eucalyptus genotypes: The importance of GxE interactions

Predicting Eucalyptus plantation productivity in the face of climate change is a key challenge for intensively managed forest plantations around the world. Forest industry tree improvement and advanced silvicultural programs are charged with maximizing forest production but face challenging selection choices where Eucalyptus genotypes may be sensitive to genetic × environment interactions (GxE). Our study investigated the importance of GXE interactions by measuring the early (establishment to 2.6 years old) cumulative growth response of 30 selected genotypes of Eucalyptus globulus, E. nitens, E. badjensis, E. smithii, E. nitens × globulus and E. camaldulensis × globulus hybrid seedlings established across contrasting water availability conditions (High vs Low Irrigation). We compared the same genotypes at a low vapor pressure deficit (VPD) and clayey soil (North site) and a high VPD sandy soil (South site) in order to evaluate the stability of these genotypes across environmental gradients and thus evaluate the importance of genetic versus environmental impacts on growth. Stand growth was evaluated at 2.6 years when leaf area index (LAI) reached canopy closure in order to estimate a growth efficiency relationship (GE) with current annual increment (CAI). As expected, irrigation increased cumulative growth and LAI for all taxas, except for E. smithii at the North site. Genotypes showed large significant differences of performance within and across sites under each irrigation treatment. However, a strong relationship between North and South cumulative volume at age 2.6 years was observed for irrigated genotypes but not for non-irrigated genotypes. This suggests that a large GxE interaction may be expected under low water resource availability conditions associated with strong effects in ranking change of evaluated taxas and genotypes. Comparing taxas with at least two genotypes or more in our experiment, GE increased under High Irrigation for all taxas across sites. However, E. nitens × globulus hybrids showed small differences between High vs Low Irrigation treatments GE relationships compared to E. nitens and E. globulus genotypes. Our results suggest the need for strategic allocation of genotypes to contrasting drought risk environments and the need to assess our understanding of how particular genotypes interact with water stress conditions.

Application of zeolite and geohumus superabsorbent on establishment and some growth indices of Nitraria schoberi L.

Using Superabsorbent is one of the solutions to water shortages in arid and semi-arid regions. In order to evaluate the effect of zeolite and geohumus on the growth of Nitraria schoberi L. species, a factorial experiment in a completely randomized design was conducted with nine replications in Kashan city. The treatments consisted of various zeolite levels (0, 10 and 15wt%) and geohumus (0, 100, 150, 250 gr for hole) and irrigation (normal irrigation, low irrigation). This study showed that superabsorbent application has a positive effect on establishment and other indices such as plant height, large and small canopy diameter and collar diameter. The highest survival percentage was observed in superabsorbent application (100%) and the lowest was measured in control treatment of low irrigation (the soil free of modifying substances) (78%). Also, the most growth indices of the plant are related to the treatment of 250g geohumus with low irrigation treatment. Based on the results, it was found that adding superabsorbent on soil causes more establishment and improves vegetative growth traits. Also, considering the economical price of zeolite superabsorbent compared to geohumus as well as its abundance in Iran, it is recommended to use in order to increase irrigation intervals and reduce costs in desertification projects.

Apparent Tolerance of Low Water Availability in Temperate Asian Bamboos1

Abstract Suitable plant water dynamics and the ability to withstand periods of low moisture input facilitate plant establishment in seasonally arid regions. Temperate bamboos are a major constituent of mixed evergreen and deciduous forests throughout temperate East Asia but play only an incidental role in North American forests and are altogether absent in the Pacific Northwest forest. Many bamboo species are classified as mesic or riparian, but none are considered drought tolerant. To assess their ability to withstand low water, we subjected five Asian temperate and one North American temperate bamboo species to three irrigation treatments: 100%, 50%, and 10% replacement of water lost through evapotranspiration. Plants were irrigated every four days over a 31-day period. Plant response to treatments was measured with stomatal conductance, leaf xylem water potentials, and intrinsic water use efficiency (iWUE). Pleioblastus distichus and Pseudosasa japonica showed significant reductions in conductance between high and low irrigation treatments. Sasa palmata had significantly lower stomatal conductance in all treatments. Pleioblastus chino displayed significantly higher iWUE in the mid irrigation treatment and Arunindaria gigantea displayed significantly lower iWUE than P. chino and S. palmata in the low irrigation treatment. The Asian bamboo species examined here tolerate low water availability and readily acclimate to different soil moisture conditions. Index words: Temperate bamboos, irrigation response, stomatal conductance, intrinsic water use efficiency. Species used in this study: Giant Cane [Arundinaria gigantea (Walt.) Muhl.]; Pleioblastus chino (Franchet & Savatier) Makino; Pleioblastus distichus (Mitford) Nakai; Pseudosasa japonica (Makino); Sasa palmata (Bean) Nakai.

Effect of sowing time and soil water content on grain yield and phenolic profile of four buckwheat (Fagopyrum esculentum Moench.) varieties in a Mediterranean environment

Four varieties of buckwheat (Fagopyrum esculentum Moench), Aizu, Botan, Hitaci and Kitawase, were evaluated using two sowing times and two irrigation treatments in a Mediterranean environment in order to ascertain a possible adaptation of this crop to this environment. Buckwheat is cultivated in particular for the high protein content and for its good biological value compared to common cereals, and for its high levels of phenolic compounds. In addition, it is gluten-free and thus suitable for people suffering from celiac disease. Overall the 4 buckwheat varieties tested in this study showed high protein content (14%, on average), although grain yield was low (420kgha−1, on average). Yield was affected by sowing time and irrigation treatment, whereas protein content was related to the variety. Low irrigation treatment (“water stress”) resulted in a lower yield (325.9kgha−1) and lower protein content (13.7%) compared to full irrigation treatment (514.7kgha−1 and 14.3%, respectively), but also in a higher content of phenolic compounds (4.46 vs. 2.79mg/g). Grain yield and phenolic fingerprint of buckwheat seeds were investigated in order to establish differences and similarities related to variety, sowing time and soil water content.

Precision nitrogen fertigation and irrigation management for improved apple quality

Nitrogen (N) management is a balance to meet tree demands for current seasons’ crop as well as for internal storage for the subsequent season whilst reducing N loss via runoff and deep drainage. Whilst fertigation is commonly practised by apple growers in Australia, research into tree nutrient requirements and therefore fertigation management strategies are limited. In the Huon valley of southern Tasmania, we applied N (Ca(NO3)2) treatments pre- and post-harvest combined with high (4 L/hr), medium (2.3 L/hr) and low (1.6 L/hr) irrigation treatments to 10 year-old ‘Galaxy’ trees grafted on M26 rootstocks. We measured yield, fruit quality attributes and fruit N content. Data from the second season revealed fruit in the low irrigation treatments were significantly smaller (152 g) but firmer, with higher total soluble solids (11.80 Brix). Irrigation treatment had no effect on fruit colour, however fruit background colour decreased significantly with increased current season N application. Fruit N content was not significantly influenced by N application. This study demonstrates the strong linkage between N and irrigation management on the above ground components of orchard production and urges caution for growers implementing pre-harvest fertigation.

Nitrous Oxide Emissions and Carbon Sequestration in Turfgrass: Effects of Irrigation and Nitrogen Fertilization (Year 1)

In this study, annual nitrous oxide (N2O) emissions were greatest in urea and least in untreated (no N) among treatments. Differences were negligible due to irrigation treatment. Irrigation levels may be decreased further in the final year to induce slight stress on the low irrigation treatment. All fertilizer treatments maintained acceptable quality, however the controlled-release fertilizer resulted in more consistent visual quality ratings compared to urea and untreated. Urea fertilizer had higher peak fluxes after fertilization and overall annual emissions than polymer-coated N-fertilizer. Thus, controlled released N fertilizers, such as polymer-coated urea, in turfgrass systems could potentially help mitigate N2O emissions.

Tree genotype modulates the effects of water deficit on a plant-manipulating aphid

Successful plant manipulation by herbivores requires a reconfiguration of the primary and secondary metabolisms of the host-plant. Water deficit is generally predicted to negatively affect the development of gall-inducing insects, by impairing their ability to remodel the primary metabolism of their host. We assessed whether host genotype could modulate water deficit effects on a gall-inducing aphid, Phloeomyzus passerinii, developing on poplars, which are known to be among the most susceptible trees to water deficit. Stem-cuttings of two poplar genotypes, with a different resistance level to P. passerinii, were grown under three irrigation treatments, and subsequently infested with the same aphid clone. Plant growth parameters and aphid colonies development were recorded, and the development and organization of the pseudogall induced by the aphid was observed using histological investigations. The three irrigation treatments resulted in three levels of water deficit. Mean predawn leaf water potential reached −0.10, −0.49 and −0.75MPa in the optimal, intermediate and low irrigation treatments respectively. In both genotypes, growth, architecture and photosynthesis were similarly affected. The severe water deficit reduced the development of aphids on both genotypes, which is in agreement with the general prediction for gall-inducing insects. Nonetheless, while the intermediate water deficit did not affect the development of aphids on the susceptible genotype, it enhanced their development on the resistant one. This latter observation contradicts the prediction for gall-inducing insects, but is in agreement with the plant stress hypothesis for sucking insects. The size of the pseudogall induced by the aphids in the bark of their host progressively diminished when water deficit increased. Lignification, believed to be an important component of poplar resistance to P. passerinii, also progressively decreased with water deficit. The involvement of physiological and architecture modifications due to water deficit on the development of aphids is discussed. The results demonstrate that host genotype can modulate water deficit effects on the development of a galling aphid, thereby compromising predictions on the outcome of droughts on stand resistance to plant-manipulating herbivores.

Modeling soil water dynamics in a drip-irrigated intercropping field under plastic mulch

Intercropping, drip irrigation, and the use of plastic mulch are important management practices, which can, when utilized simultaneously, increase crop production and save irrigation water. Investigating soil water dynamics in the root zone of the intercropping field under such conditions is essential in order to understand the combined effects of these practices and to promote their wider use. However, not much work has been done to investigate soil water dynamics in the root zone of drip-irrigated, strip intercropping fields under plastic mulch. Three field experiments with different irrigation treatments (high T1, moderate T2, and low T3) were conducted to evaluate soil water contents (SWC) at different locations, for different irrigation treatments, and with respect to dripper lines and plants (corn and tomatoes). Experimental data were then used to calibrate the HYDRUS (2D/3D) model. Comparison between experimental data and model simulations showed that HYDRUS (2D/3D) described different irrigation events and SWC in the root zone well, with average relative errors of 10.8, 9.5, and 11.6 % for irrigation treatments T1, T2, and T3, respectively, and with corresponding root mean square errors of 0.043, 0.035, and 0.040 cm3 cm−3, respectively. The results showed that the SWC in the shallow root zone (0–40 cm) was lower under non-mulched locations than under mulched locations, irrespective of the irrigation treatment, while no significant differences in the SWC were observed in the deeper root zone (40–100 cm). The SWC in the shallow root zone was significantly higher for the high irrigation treatment (T1) than for the low irrigation treatment, while, again, no differences were observed in the deeper root zone. Simulations of two-dimensional SWC distributions revealed that the low irrigation treatment (T3) produced serious severe water stress (with SWCs near the wilting point) in the 30–40 cm part of the root zone, and that using separate drip emitter lines for each crop is well suited for producing the optimal soil water distribution pattern in the root zone of the intercropping field. The results of this study can be very useful in designing an optimal irrigation plan for intercropped fields.

Effect of 10-year continuous saffron cultivation on physical and chemical properties of soil

The effect of 10-year continuous saffron cultivation on physical and chemical properties of a silty clay loam soil was investigated in a research farm of College of Agriculture, Shiraz University, Shiraz (52 o 33ʹ E Longitude and 29o 36ʹ N latitude), Iran. This farm was irrigated with different regimes (100% of saffron's potential evapotranspiration (ETp), 75%ETp, 50%ETp) including rain fed treatment under two irrigation methods (basin and furrow irrigation). The results showed that the values of electrical conductivity, sodium adsorption ratio, Arsenic, Boron and soil bulk density of soil in the root zone increased significantly, but the final infiltration rate decreased significantly compared to the original soil. The value of pH in 100%ETp and 75%ETp treatments decreased and in 50%ETp and rain fed treatments increased compared to the original soil. Corms under high irrigation treatment had more weight up to a 6-year cultivation. However, after that, the corm weight declined to levels equal to or less than the low irrigation treatment cases. The number of total corms increased up to 6 years of cultivation and decreased after that. So, the continuous saffron cultivation causes some undesirable change in soil chemical and physical properties, which become pronounced after 6 years of cultivation.

The Effects of Irrigation Level and Genotype on Pod-Filling Related Traits in Peanut (Arachis hypogaea)

In peanut (Arachis hypogaea), pod-filling is an important biological stage that is strongly influenced by the availability of water. It also has genetic component; since genotypes vary considerably in their pod-filling potential. We studied the effects of irrigation level, genotype and the Irrigation Level × Genotype interaction on pod-filling and other pod-related traits of peanut. Four peanut genotypes, including three Virginia-types and one Peruvian-type which differ considerably in their pod-filling potential, were examined under field conditions. Four irrigation treatments were applied (60%, 80%, 100% and 120%) in a factorial experimental design. A significant irrigation-treatment effect was observed for the two main pod-filling related traits, meat content and dead-end ratio, in all of the genotypes studied. The irrigation level significantly affected gross pod weight, 100-pod weight and 100-seed weight, but did not have any significant effects on pod yield per plot or pod size distribution. Therefore, our study suggests that reduction in irrigation directly influence the developing pods, as a result of low water availability/potential in the pod’s surrounding environment. The effect of irrigation was most significant at the lowest irrigation level (60%); whereas a milder effect was observed in the 80% irrigation treatment, indicating that, in some cases, it is possible to reduce irrigation down to 80% without affecting the pod-filling components. Although the Irrigation × Genotype interaction was not statistically significant, some genotypes were found to be more strongly affected by the low-irrigation treatments. Also, irrigation level significantly affected the incidence of pod wart and the pod color variables, suggesting that higher irrigation should be applied in order to address these marketing-related traits. This trial serves as a fundamental study for understanding the pod-filling components that are influenced by the irrigation level in peanut.

Grasses for biofuels: A low water-use alternative for cold desert agriculture?

In arid regions, reductions in the amount of available agricultural water are fueling interest in alternative, low water-use crops. Perennial grasses have potential as low water-use biofuel crops. However, little is known about which perennial grasses can produce high quantity, high quality yields with low irrigation on formerly high-input agricultural fields in arid regions. We monitored biomass production, weed resistance, rooting depth, and root architecture of nine perennial grasses under multiple irrigation treatments in western Nevada. Under a low irrigation treatment (71 ± 9 cm irrigation water annually), cool-season grasses produced more biomass and were more weed-resistant than warm-season grasses. With additional irrigation (120 ± 12 cm water annually), warm- and cool-season grasses had similar biomass production, but cool-season species remained more weed-resistant. Among species within each grass type, we observed high variability in performance. Two cool-season species (Elytrigia elongata and Leymus cinereus) and one warm-season species (Bothriochloa ischaemum) performed better than the other tested species. Root depth was not correlated with biomass production, but species with deeper roots had fewer weeds. Abundance of fine roots (but not large roots) was correlated with increased biomass and fewer weeds. Both L. cinereus and E. elongata had deep root systems dominated by fine roots, while B. ischaemum had many fine roots in shallow soil but few roots in deeper soil. Cool-season grasses (particularly E. elongata, L. cinereus, and other species with abundant fine roots) may be worthy of further attention as potential biofuel crops for cold desert agriculture.

NUTRITION AND IRRIGATION: TOWARDS A PRACTICAL SOLUTION FOR CHERRY CRACKING

Fruit cracking in sweet cherries is an economically significant problem for growers world-wide and is associated with late season rainfall. Building resilience into fruit from an early stage in order to withstand rapid excess water entry without cracking, is important. This trial assessed calcium (Ca) levels and fruit characteristics of sweet cherry fruit produced under three different irrigation volumes, following on previous research suggesting low irrigation increased cracking susceptibility. In the present study, higher irrigation volumes also resulted in reduced cracking levels at harvest. Given the structural role of Ca in plant cells and that Ca is xylem mobile, it was hypothesised that higher irrigation volumes may favour the uptake and incorporation of Ca into fruit cells. While Ca concentration increased with increased irrigation levels at harvest (when cracking occurs) Ca concentration was not significantly different between treatments. Both the high and low irrigation treatments resulted in fruit with increased firmness and skin puncture force compared to the medium (commercial orchard practice) irrigation level. This provided information about building resilience to cracking in sweet cherry fruit, highlighted the importance of both nutrition and irrigation in managing risk and applies the knowledge to provide solutions to a very real dilemma. The findings will be important for the development of future cherry fruit cracking management strategies, which may need to be considered early, rather than later during fruit growth.

β-Carotene yield and productivity of orange-fleshed sweet potato (Ipomoea batatas L. Lam.) as influenced by irrigation and fertilizer application treatments

β-Carotene rich orange-fleshed sweet potatoes are increasingly used in community-based interventions aimed at addressing vitamin A deficiency, but are often cultivated in marginal soils and with sub-optimal agricultural inputs. The aim of the study was to determine (i) β-carotene content, β-carotene yield and water productivity at increments of water application, and, (ii) β-carotene content and β-carotene yield at increments of chemical fertilizer application for orange-fleshed sweet potato in separate field trials. β-Carotene content at the low irrigation treatment was between 15 and 34% higher than at optimal irrigation treatment. Increased water application brought about a two-fold increase in β-carotene yield per unit area. The best combination of β-carotene yield and water productivity (g β-carotene ha−1mm−1 water applied) was achieved at the intermediate (60%) irrigation treatment. Calculations showed that 1ha of orange-fleshed sweet potato produced at the intermediate water application at yield level of 24.6–28.4tha−1, can potentially provide 452–730 households (of six persons) with an adequate amount of vitamin A over a period of 180days. β-Carotene content was 14% higher for both intermediate (50%) and high (100%) fertilizer treatments, compared to the 0% fertilizer treatment. β-Carotene yield increased two-fold at the intermediate and four-fold at the high fertilization treatment. This paper provides novel information on the effect of irrigation on β-carotene yield, as well as β-carotene water productivity in orange-fleshed sweet potato. Follow-up research on a range of varieties is suggested toward obtaining recommendations for broad application in vitamin A crop-based interventions to optimize the β-carotene yield in orange-fleshed sweet potato.