Conventional Deficit Irrigation Research Articles

Physiological and agronomic response of young ‘Verna’ lemon trees to the application of partial root irrigation compared to conventional deficit irrigation under conditions of high evaporative demand

Physiological and agronomic response of young ‘Verna’ lemon trees to the application of partial root irrigation compared to conventional deficit irrigation under conditions of high evaporative demand

English

Drought is a highly important abiotic stress that affects crops around the world and especially under the Mediterranean climate. This study is focused on strawberry, an important species around the Mediterranean that is suitable for family-owned smallscale businesses. This study aimed to determine the effects of conventional deficit irrigation and fixed partial root drying techniques on the evapotranspiration (ET), yield and quality of Rubygem strawberry species. Strawberry seedlings were planted in the greenhouse in a double row at a planting distance of 30×30 cm. Irrigation was carried out by drip irrigation. The control - full irrigation was based on measurements taken from an A-Class Evaporation Pan. Three conventional deficit irrigation (DI80, DI60 and DI40) and four fixed partial root drying (FPRD100, FPRD80, and FPRD60 FPRD40) were examined. Irrigation water quantities were applied at the 100% (FPRD100/FULL), 80% (DI80 and FPRD80), 60% (DI60 and FPRD60) and 40% (DI40 and FPRD40) levels. The amount of irrigation water ranged between 199.17 and 452.92 mm. It was found that the various water levels affected the ET and the yield (Y). In general, as the amount of water decreased, the ET also decreased. The ET, Y, water use efficiency (WUE) and irrigation water use efficiency (IWUE) were significantly affected by irrigation treatments (LSD 5%). The yield values are ranked from high to low as FULL > FPRD100 > FPRD80 > DI80 > DI60 > FPRD60 > FPRD40 > DI40. As expected, WUE and IWUE values were higher under deficit irrigation levels i.e., DI80, DI60, DI40, FPRD80, FPRD60, and FPRD40. Fruit quality parameters (width, height and average weight) increased with the increase in the amount of applied irrigation water. In addition, fruit firmness values and total phenolic compounds were significantly affected by irrigation level. The results showed that different irrigation levels (100%, 80%, 60% and 40%) affected the yield and yield parameters of strawberry plants. In general, it has been found that, the yield and quality are negatively affected with increases in water deficit (DI40 and FPRD40 treatments). However, the results showed that the fixed partial root drying technique is superior to conventional deficit irrigation applications. As a result of the research, mainly FPRD80 and then DI80, DI60 and FPRD60 are recommended for strawberry cultivation, especially in arid and semiarid regions, depending on the availability of water

Determination of the Effect of Different Irrigation Regimes on Some Quality Properties of Cucumber

This study aimed to examine the effects of varying levels of deficit irrigation applied through partial root drying (PRD) and conventional deficit irrigation on some parameters of cucumber plant such as fresh and dried biomass, plant stem diameter, number of leaf, fruit length, fruit diameter, fruit weight, water soluble dry matter (WSDM). Seven irrigation treatments (DI75, APRD75, FPRD75, DI50, APRD50, FPRD50) were examined together with the control treatment (FULL). The irrigation water of the treatments DI75, APRD75 and FPRD75 are 25% less than the FULL treatment. The irrigation water of the DI50, APRD50 and FPRD50 treatments is 50% less than the FULL treatment. DI75 and DI50 are traditional deficit irrigation applications in which both sides of the plant root zone are wetted. In APRD75 and APRD50 treatments, one half of the plant root zone is wetted and the other half is left dry and the wet/dry parts are switched in each irrigation application. In FPRD75 and FPRD50 treatments, one half of the plant root zone is wetted and the other half is left dry for a fixed period during the entire season. It has been revealed that 25% and 50% water deficit levels affect the amount of biomass as a result of the application of conventional deficit irrigation and partial root drying (PRD) techniques when compared to the FULL treatment. However, it has been found that the parameters such as plant stem diameter, fruit length, fruit diameter, fruit weight and WSDM are not affected. When the results obtained in the research are evaluated; it has been observed that water application techniques (DI, APRD, FPRD) have a significant effect on both plant development and yield when the same amount of water is given. As irrigation water constraint increases, the yield has been found to decrease. However, the decrease in the amount of irrigation water and the decrease in yield have not been the same. Research aiming to save irrigation water is increasingly important, especially in arid and semi-arid regions where water is scarce and expensive. In this regard, the fact that the decrease in yield remains smaller than the rate of decrease in irrigation water can be seen as an advantage of PRD treatments.

Assessment of crop water stress index and net benefit for surface- and subsurface-drip irrigated bell pepper to various deficit irrigation strategies

AbstractThis study addresses the assessment of crop water stress index (CWSI) of bell pepper (Capsicum annuum L.) and net income generated under regulated deficit irrigation (RDI), conventional deficit irrigation and partial root-zone drying (PRD) and full irrigation (I100) using surface- and subsurface-drip systems (DI and SDI) during 2016 and 2017 in the Mediterranean region. The experimental design was split-plots with four replications. RDI was supplied with 50% of I100 during vegetative stage until flowering, then received 100% of crop water requirement. PRD50 received 50% of I100, but from alternative laterals each watering. The results revealed that CWSI was correlated significantly (P < 0.01) and negatively with yield, yield per plant, total soluble solid, ETa, fruit weight and plant height indicating that yield of bell pepper declined with increasing CWSI values (P < 0.01). Bell pepper should be irrigated at mean CWSI value of 0.20 without any yield reduction. CWSI in the RDI and I75 treatments were slightly greater than 0.20. Irrigation treatments had significant effect on yield and quality traits. The highest total soluble solutes were found in PRD50 and I50. The DI I100 treatment generated the highest net income followed by the SDI I100 and RDI. In conclusion, RDI and I75 appear to be good alternatives to I100 for sustainable bell pepper production in the Mediterranean region.

Yield, dry matter and water productivity simulation for surface and subsurface drip-irrigated bell pepper using the SALTMED model

AbstractSALTMED model performance was evaluated by comparing simulated and observed soil water content, dry matter (DM) yield, yield and water productivity (WP) data of field-grown bell pepper (Capsicum annuum L.) under Mediterranean climatic conditions irrigated with surface and subsurface drip systems. Simulation data were obtained from field experiments performed in 2016 and 2017. Treatments were full irrigation (I100), conventional deficit irrigation at 75 and 50% actual crop evapotranspiration (ETa; I75 and I50), regulated-deficit irrigation (RDI) and partial root-zone drying (PRD) at 50% ETa using surface (SfDI) and subsurface drip systems (SbDI) on a clay-loam soil, in a split-plot with four replications. Results showed that 56 and 29 mm less irrigation water was applied to SdDI100 in 2016 and 2017, respectively, than SfDI100; RDI used 27 and 77 mm less irrigation water than SfDI100 in experimental years, respectively. SbDI and SfDI performed similarly for bell pepper yield, DM and WP. However, the effect of irrigation treatments on yield, DM and WP was significant. I100 showed the highest yield (74.9 and 71.1 t/ha in 2016 and 2017, respectively), followed by RDI in 2016; I100, RDI and I75 produced greater yield than other treatments in 2017. PRD50 and I50 produced the least yield (49.8 and 45.9 t/ha in 2016 and 2017, respectively). SbPRD50 and SbI50 had the greatest WP value under SbDI in the experimental years. Results showed that the SALTMED model simulated yield, DM, soil water content and WP reasonably well (R2 = 0.95, 0.97, 0.98 and 0.74, respectively).

Response of Greenhouse Grown Cucumber to Partial Root Zone Drying and Conventional Deficit Irrigation

Bu araştırmada, serada yetiştirilen hıyar bitkisinin yarı ıslatmalı sulama (YIS) ve geleneksel kısıntılı sulamaya (KS) tepkisinin belirlenmesi amaçlanmıştır. Çalışma, Türkiye’nin güneyinde Antalya koşullarında plastik örtülü ve cam olmak üzere iki farklı serada yürütülmüştür. Kontrol konu (K100) ile birlikte iki geleneksel kısıntılı sulama (KS75 ve KS50), ardışık-yarı ıslatmalı sulama (A-YIS75 ve A-YIS50) ve sabit-yarı ıslatmalı sulama (S-YIS75 ve S-YIS50) olmak üzere yedi sulama konusu ele alınmıştır. Sulama suyu (mm), verim (t ha-1), bitki boyu (cm), kuru madde vb gözlem ve ölçümler yapılmıştır. Sulama suyu kullanım randımanı (SSKR) değerleri (kg (ha×mm)-1) hesaplanmıştır. Beklenildiği gibi, K100 kontrol konusu toprak su içeriği en yüksek değerlerde ve tarla kapasitesi yakın bir seyir izlemiştir. Diğer konularda ise bitki kök bölgesi toprak su içeriği K100 konusundan daha düşük düzeyde kalmıştır. Toplam verim değerlerinin istatistiksel analizi sonucu Tukey’s %5 düzeyinde sulama konuları arasındaki fark önemli bulunmuştur. İlk yıl K100, KS75, S-YIS75, A-YIS75 ve A-YIS50 konuları istatistiki olarak en yüksek verim değerlerinde yer almış ve aralarında istatistiki olarak bir fark bulunmamıştır. Yine ilk yıl, S-YIS50 ve KS50 konuları ise istatistiki olarak en düşük verim değerlerine sahip olmuştur. İkinci yıl, birinci yıla benzer bir şekilde ancak, sadece K100 ve S-YIS75 konuları istatistiki olarak en yüksek verim değerlerine sahip olmuş ve aralarında istatistiki olarak bir fark bulunmamıştır. Yine ikinci yıl, KS50 konusu istatistiki olarak en düşük verim değerine sahip olmuştur. SSKR değeri her iki yıl en yüksek A-YIS50 konusunda hesaplanmıştır. En düşük SSKR değeri ise birinci yıl KS50, ikinci yıl ise A-YIS75 konularında belirlenmiştir. Araştırmada, genel olarak, sulama suyunun kısıntı düzeyi artıkça verimde azalma saptanmıştır. Sulama suyundan tasarruf sağlamaya yönelik araştırmalar özellikle suyun kıt ve pahalı olduğu kurak ve yarı kurak bölgelerde önemini gittikçe artırmaktadır. Bu bağlamda, verimdeki düşüşün sulama suyundaki azalma oranından daha küçük kalması, YIS konularının bir avantajı olarak görülebilir.

Biochar and alternate wetting-drying cycles improving rhizosphere soil nutrients availability and tobacco growth by altering root growth strategy in Ferralsol and Anthrosol

Biochar has been advocated as a sustainable and eco-friendly practice to improve soil fertility and crop productivity which could aid in the mitigation of climate change. Nonetheless, the combined effects of biochar and irrigation on tobacco growth and soil nutrients in diverse soil types have been incompletely explored. We applied a split-root experiment to investigate the impacts of amendment with 2% softwood- (WBC) and wheat-straw biochar (SBC) on growth responses and rhizosphere soil nutrients availability of tobacco plants grown in a Ferralsol and an Anthrosol. All plants within same soil type received same amount of water daily by either conventional deficit irrigation (CDI) or alternate wetting-drying cycles irrigation (AWD). Compared to the un-amended controls, SBC addition enhanced biomass, carbon (C)-, phosphorus (P)- and potassium (K)-pool in the aboveground organs especially in Anthrosol, despite a negative effect on aboveground nitrogen (N)-pool. Regardless of soil type, biochar combined with AWD lowered root diameter while increased root tissue mass density to engage the plant in an acquisitive strategy for resources, therefore altered leaves stoichiometry as exemplified by lowered N/K, C/P and N/P and increased C/N. The addition of SBC induced a liming effect by increasing Anthrosol soil pH which was further amplified by AWD, but was unaffected on Ferralsol. Moreover, compared to the controls, SBC and AWD increased available P and K, and total C, total N and C/N ratio in the rhizosphere soil which coincided with the lowered soil C and N isotope composition (δ13C and δ15N), though a slight reduction in C and N stocks under AWD. However, such effects were not evident with WBC might be associated with its natures. Thus, combined SBC/AWD application might be an effective strategy to synergistically overcome nutrients restriction and improve tobacco productivity by intensifying nutrients cycling and optimizing plant growth strategies.

A review on Partial root-zone drying (PRD): A modern irrigation technique

Field experiments were conducted for 3 years from 2000 to 2002 to assess proportional crop yield differences obtained under conventional deficit irrigation (CDI) and partial root-zone irrigation (PRI) practices, compared with full irrigation (FULL) where plant water requirements were fully met. The experimental crops included vegetables (tomato and pepper), field crops (maize and cotton) and citrus. The fruit yield of greenhouse-grown tomato with FULL irrigation was higher than with PRI (7–22% lower) but was not significantly different. The PRD irrigation is a novel improvement of deficit irrigation in which half of the root zone is irrigated alternatively in scheduled irrigation events. In the last decade, scientists across the world, especially from arid to semi-arid countries, have extensively evaluated this irrigation as a water-saving irrigation strategy on agronomic and horticultural plants. This review paper focuses on the physiological and morphological aspects of PRD on plants and its ultimate impact on yield and water productivity. Overall, under limited water resources where water is precious, PRD is a viable irrigation option to increase water productivity while margining the yield, rather than only increasing the economic yield without concerning the value of water in limited water environments.

Yield and water productivity response of quinoa to various deficit irrigation regimes applied with surface and subsurface drip systems

AbstractThis study evaluated the yield and water productiivty response of quinoa to regulated deficit irrigation (RDI), partial root-zone drying (PRD) and conventional deficit irrigation (DI) and full irrigation (FI) using surface (SD) and subsurface drip (SSD) systems in 2016 and 2017 in the eastern Mediterranean region of Turkey. The treatments consisted of RDI, PRD50, DI50, DI75 and FI. A rainfed treatment (RF) was also included in the study. The experimental design was split plots with four replications. DI75 and DI50 received 75 and 50% of FI, respectively. PRD50 received 50% of FI, but from alternative laterals. RDI received 50% of FI during vegetative stage until flowering, and then received 100% of water requirement. The results showed that quinoa under SD used slightly more water than SSD due to reduced surface evaporation. RDI resulted in water saving of 23 and 21% for SD and SSD, respectively, compared to FI; and RDI produced statistically similar grain yields to FI. DI75 treatment resulted in water savings of 16% for both drip methods in the first year and 10 and 25% for SD and SSD systems, respectively, in the second year. PRD50 produced greater yield than DI50 eventhough they received the same amount of irrigation water. RF and PRD50 treatments resulted in significantly greater water productivity (WP) values than other treatments. There was no significant difference between SD and SSD regarding the grain and dry matter yields and WP values. Thus, RDI and DI75 appear to be good alternatives to FI for sustainable quinoa production in the Mediterranean region.

Environmental Mitigation Through Irrigation Management in Sugar Beet Production

This study assessed the greenhouse gas (GHG) emissions of sugar beet production under different irrigation and fertilizing strategies. This manuscript is an evaluation of the on production inputs used in a research carried previous on sugar beet and its conversion into GHG emissions equivalent. This paper evaluated the potential for environmental mitigation, including the reduction of total GHG emissions from agricultural inputs in sugar beet production by managing irrigation and nitrogen fertilizing. In this context, the nine treatments based on three different irrigations (full irrigation, conventional deficit irrigation, partial root drying irrigation) and three nitrogen fertilizing strategies (full nitrogen, partial deficit nitrogen, moderate deficit nitrogen) were assessed. The results of evaluation showed that DI-N 1 strategy can reduce irrigation water and nitrogen use up to 25% compared to control treatment (FI-N). In addition, this strategy saved 25% of electricity consumption use for irrigation. The analyse of pollution in this study led to very important findings: more environment-friendly irrigation and fertilization practices by using less water and nitrogen have a considerable potential for environmental mitigation in sugar beet production

Water Saving and Yield of Potatoes under Partial Root-Zone Drying Drip Irrigation Technique: Field and Modelling Study Using SALTMED Model in Saudi Arabia

This study aims to evaluate the Partial Root Zone Drying Irrigation System (PRD) as one of the modern technologies that provide irrigation water and increase the efficiency of its use on potato crop. The effect of applying the PRD conventional deficit irrigation (CDI) on the efficiency and water saving in potato crops using the drip surface (S) and subsurface (SS) irrigation methods were investigated. SALTMED model used to predict soil moisture and salinity distribution, soil nitrogen dynamics, and yield of potato crop using the different irrigation levels (150%, 100%, and 50% of Crop evapotranspiration (ETc)). The study showed that the water use efficiency (WUE) decreases with increasing levels of irrigation water, as it ranged between 2.96 and 8.38 kgm−3, 2.77 and 7.01 kgm−3 for surface irrigation PRD and CDI, respectively, when the amounts of irrigation water varied from 308 mm to 1174 mm, respectively. The study showed that the irrigation efficiencies were the highest when using PRD system in all treatments when irrigating the potato crop during the spring season, and it was more efficient in the case of using subsurface irrigation method. The results show that the soil moisture (SM) was high in 25–45 cm at 150% of ETc was 0.166 and 0.263 m3m−3 for the first and last stages of growth, respectively. 100% of ETc, (SM) was 0.296 m3m−3 at 0–25 cm, 0.195 m3m−3 at 25–45 cm, 0.179 m3m−3 at 45–62 cm, depths, respectively. whereas 50% of ETc, (SM) was 0.162 m3m−3 at 0–25 cm, 0.195 m3m−3 at 25–85 cm, depths. At 100% of ETc, soil salinity was 5.15, 4.37, 3.3, and 4.5 dSm−1, whereas at 50%, ETc, these values were 5.64, 9.6, 3.3, and 4.2 dSm−1. Statistical indicators showed that the model underestimated yield, for 150%, 100%, and 50% of ETc. Therefore, it can be concluded that yield and WUE using PRD systems were the highest in the potato crop compare to CDI surface and sub-surface, and SALTMED model can predict the moisture distribution, salinity, and yield of potatoes after accurate adjustment.

The effects of water stress on yield performance of drip-irrigated pepper (Capsicum annum L. cv. Capya var. Yalova yağlık 28) in the Central Anatolian region of Turkey

The aim of this study is to investigate the effects of conventional deficit irrigation strategy on yield components and water use efficiency in the red pepper. The field study was performed in Cumra, a town in the province of Konya in the years of 2012 and 2013. The irrigation treatments were applied as follows: (i) full irrigation regime (100% of water requirement for plant, I100) and (ii) two conventional deficit irrigations regime at the rate of 80% (I80) and 60% (I60) of I100 at 5-day intervals. The irrigation water was used based on soil water content measurement through the gravimetric method where evaporation was measured by a class A pan cup simultaneously. The maximum marketable yields were obtained in the treatment of I100 with 22.0 and 24.0 t ha−1 for the years of 2012 and 2013, respectively. The seasonal crop water requirement was calculated as 454, 591, and 726 mm for 2012 and as 498, 652, and 806 mm for 2013, respectively. The values of crop yield response factors (ky) at I80 and I60 were found as 1.03 and 1.37 in 2012 and 0.66 and 1.54 in 2013, respectively. The highest levels of water use efficiency (WUE) and irrigation water use efficiency (IWUE) were determined for the treatment of 20% deficit during the period of study. The complete irrigation levels (FC) were calculated through 0.87 times the pan A evaporation. The results reveal that full irrigation strategy is the best choice to obtain maximum yield or net return while 20% deficit irrigation is a viable solution for water poor environments.

Partial root-zone irrigation effects on growth, metabolism and calcium status of Mangosteen seedling (Garcinia mangostana L.)

Efficient irrigation technique for mangosteen seedling was evaluated, from October 2016 to May 2017, in order to determine the growth and morphophysiology of both the conventional deficit irrigation (CD) and partial root-zone irrigation (PR). A set of randomized block design, with 4 replicates each, was applied on 100% field capacity (control), 50% field capacity (CD1), 30% field capacity (CD2), and ratios of 100:50% field capacity (PR1), 100%:30% field capacity (PR2) and 50:30% field capacity (PR3). The results showed a restriction in mangosteen growth, except control, as indicated by decrease in total dry mass, which due to decrement in leaf number, photosynthetic rate and root growth. Malondialdehyde (MDA) level and glutathione peroxidase (GPX) activity was higher while proline accumulation was lower in PR compared to those of both CD and control treatments. Secondary metabolites content changes in treatments, such as octacosane, cysteamine sulfonic acid, propyl oleate, 1-nanodecene, and 2-butyn-1-ol-4metoxy were synthesized in the low soil moisture conditions. Leaf Ca-pectate, Ca-phosphate and dissolved Ca tended to increase in low soil moisture. The PR1 treated plant had the highest water use efficiency. Therefore, PR technique could be applied when the soil moisture level represents 50% (or more) of the field capacity

Yield and resource use efficiency of Plukenetia volubilis plants at two distinct growth stages as affected by irrigation and fertilization

This study is to test how seedlings (vegetative) and large plants (reproductive) of an oilseed crop (Plukenetia volubilis) responded to regulated deficit irrigation techniques (conventional deficit irrigation, DI; alternative partial root-zone irrigation, APRI) in a tropical humid monsoon area. Seedlings were more sensitive to water deficit than large plants. Although APRI did better than DI in saving water for both seedlings and large plants at the same amount of irrigation, full irrigation (FI) is optimal for faster seedling growth at the expense of water-use efficiency (WUE). The seed number per unit area was responsible for the total seed oil yield, largely depending on the active process of carbon and nitrogen storages at the whole-plant level. The magnitude of the increase in total seed and seed oil yield by fertilization was similar under different irrigation regimes. Compared with FI, DI can save water, but reduced the total seed yield and had lower agronomic nutrient-use efficiency (NUEagr); whereas APRI had similar total seed yield and NUEagr, but reduced water use greatly. Although the dual goal of increasing the yield and saving water was not compatible, maintaining a high yield and NUEagr at the cost of WUE is recommended for P. volubilis plantation in t he water-rich areas.

Evaluation of crop water stress index on Royal table grape variety under partial root drying and conventional deficit irrigation regimes in the Mediterranean Region

This research was conducted during 2009, 2010 and 2012 growing seasons in the experimental vineyard of the Department of Horticulture at Cukurova University in Adana located in the Eastern Mediterranean Region of Turkey on 12 years old Royal table grape variety to evaluate the crop water stress index under various deficit and partial rootzone drying irrigation strategies applied with drip system. In the study, six different treatments were considered; namely full irrigation (FI), deficit irrigations (DI-75 and DI-50), partial rootzone drying (PRD-75 and PRD-50) and rainfed (RF). In FI soil water deficit in the 80cm within the seven-day intervals was replenished to the field capacity. DI-75, DI-50, and PRD-75, PRD-50 treatments received 75 and 50% of water applied to FI. In PRD plots, drip laterals on both sides of the vine rows operated alternately. Experimental design was randomized blocks with three replications. Canopy temperatures were measured throughout the growing season with an infrared thermometer, and vapor pressure deficit of air was used for calculating the crop water stress index (CWSI). Lower and upper limits of basic graphic, which is necessary to CWSI calculation, were developed for grapevine. The effect of irrigation treatments on yield, vine growth and juice quality differred significantly among the treatments. Highest yield was obtained from the full irrigation (FI) as 30.2tha−1, and the lowest yield was obtained from the RF treatment as 14.2tha−1. PRD vines exhibited a stronger control over vegetative growth as compared with DI and FI plants. This was expressed by lower values of total leaf area at harvest. Higher water use efficiency (WUE) was observed in RF and PRD-75 treatments while the lowest WUE was obtained from DI-50 treatment. Results showed significant differences in grape quality components among treatments and seasons studied. The highest brix value was obtained in RF while the lowest brix value was from the FI treatment. Three years seasonal average CWSI values ranged from 0.20 in FI to 0.77 in RF. Significant linear relations were found between yield and CWSI in three experimental years. The results revealed that Royal variety should be irrigated when average CWSI value is approximately 0.20 for high yield. According to the experimental findings, PRD-75 application with water savings as compared to full irrigation might be a suitable strategy for irrigation under water scarcity.

Root and leaf abscisic acid concentration impact on gas exchange in tomato (Lycopersicon esculentum Mill) plants subjected to partial root-zone drying

Partial root-zone drying (PRD) is a deficit irrigation technique with great potential for water saving. A split-root experiment was conducted on tomato in controlled environment in order to test the response of two long-time storage cultivars to PRD. Ponderosa tomato, a cultivar with yellow fruits, was compared to Giallo tondo di Auletta, a local cultivar from southern Campania (Italy). Plants were subjected to three irrigation treatments: plants receiving an amount of water equivalent to 100% of plant evapotranspiration (V100); plants in which 50% of the amount of water given to V100 was supplied (V50); and plants where one root compartment was irrigated at 50% of water requirements and the other compartment was allowed to dry, and thereafter every side was rewetted alternatively (PRD). The highest levels of leaf abscisic acid (ABA) [on average equal to 104 ng g–1 fresh weight FW)] were measured in PRD and V50, at 70 days after transplantation. Root ABA concentration in both PRD and V50 reached mean values of 149 ng g–1 FW. There were differences for the irrigation regime in root ABA biosynthesis and accumulation under partial root-zone drying and conventional deficit irrigation (V50). Assimilation rate, stomatal conductance and intercellular CO2 concentration decreased in relation to the irrigation regime by 22, 36 and 12%, respectively, in PRD, V50 and V100 at 50 days after transplantation. Ponderosa variety accumulated 20% more dry matter than Auletta and significant differences were observed in leaf area. In both PRD and V50 of the two varieties, it was possible to save on average 46% of water. Our results indicate that there is still space to optimise the PRD strategy, to further improve the cumulative physiological effects of the root-sourced signaling system.

Performance of partial root-zone drip irrigation for sugar beet production in a semi-arid area

Partial root-zone drying (PRD), a water-saving irrigation strategy, is being tested in many field crops species. In this study, the effects of PRD on root yield, sugar yield, water use efficiency (WUE), and fertilizer-nitrogen use efficiency (FNUE) of field-grown sugar beet were compared with those of conventional deficit irrigation (CDI) and full irrigation (FI). The experiments were conducted at Konya-Çumra, a Central Anatolian region of Turkey, in 2012 and 2013. Five irrigation techniques were designed and three nitrogen levels were chosen for the current study. These five irrigation techniques were applied to the study crops with the help of a drip irrigation system. In FI (control), the irrigation water was applied to both sides of the root system such that 35–40% of the available soil moisture was consumed in the 0.90-m root zone. In CDI50 and CDI75, 50% and 75% irrigation water of FI, respectively, was supplied to both sides of the root system. In alternative PRD50 (APRD50), the half of the root system was exposed to soil drying and the other half was kept well-watered with 50% irrigation water of FI. In fixed PRD50 (FPRD50), 50% irrigation water of FI was supplied only to half of the fixed side of the root system. Furthermore, the three chosen nitrogen levels included N100, where the plant’s nitrogen requirement is met completely; N75, where 25% reduction was made in the plant’s nitrogen requirement; and N50, where 50% reduction was made in the plant’s nitrogen requirement. Although the effect of nitrogen levels on sugar beet root and sugar yields was not significant, irrigation treatments had a significant effect (5% of the level). Compared to the FI treatment, the CDI75, CDI50, APRD50, and FPRD50 treatments decreased the standardized root and sugar yields by 6.36%, 26.97%, 19.12%, and 23.50%, respectively. APRD50 and FPRD50 increased the standardized yield by 10.74% and 4.75% compared to CDI50, respectively. In addition, when same amount of irrigation water was used, PRD (APRD50 and FPRD50) treatments outperformed CDI50 in WUE and FNUE of sugar beets. Compared to FI and CDI50, APRD50 increased WUEroot by 19.8% and 8.5% and FNUEroot by 26.2% and 68.2%, respectively. The varying nitrogen levels had a significant effect on FNUEroot and FNUEsugar. The highest FNUEroot and FNUEsugar values were obtained with N50. Further, combinations of different irrigation treatments and nitrogen levels had a significant effect on FNUEroot.

Nutritional responses to soil drying and rewetting cycles under partial root-zone drying irrigation

Repeated soil drying and rewetting (DRW) cycles occur in rainfed and irrigated agriculture. The intensity and frequency of DRW cycles regulate both microbial physiology and soil physical processes, hereby affecting the mineralization and immobilization of soil nutrients and their bioavailability. Partial root-zone drying irrigation (PRI) irrigates half of the soil zone, while the other half is allowed to dry, and the two halves is alternately irrigated. PRI outweighs conventional deficit irrigation in further improving water use efficiency (WUE) by enhancing the root-to-shoot chemical signaling that regulates stomatal aperture. PRI induced soil DRW cycles and more soil water dynamics in the root zone enhance soil nutrient mineralization process and thus increase the bioavailability of soil nutrients, resulting in improved nitrogen (N) and phosphorus (P) uptake, in which soil microbial processes play a key role. Studies investigating how soil DRW cycles and water dynamics under PRI on nutrient transport in soil solution, soil microbe mediated P transformation, interactions between phytohormones and nutrient uptake, root morphological and architectural traits for nutrient acquisition, and PRI-integrated fertigation are still lacking. In addition, the positive nutritional effect may be varied in terms of climatic conditions and intensity and frequency of precipitation or irrigation, and these merit further in-depth studies.

Evaluation of soil chemical properties irrigated with recycled wastewater under partial root-zone drying irrigation for sustainable tomato production

Recycling of wastewater is becoming more popular in order to augment the inadequate irrigation supplies and meet the growing water demands for agriculture in arid regions of the world. This study investigated the environmental impact of deficit irrigation regimes on soil properties with five scenarios using recycled wastewater (RW), fresh tap water (FW), and a blend of RW and stormwater (BW). The five irrigation scenarios were applied to tomato plants growing in pots and included: (i) full irrigation (FI); (ii) partial root zone drying (PRD) irrigation at 75% of FI involving irrigation of only one part of the root zone, while the other part was exposed alternately to soil drying (PRD 75); (iii) PRD irrigation at 50% of FI (PRD 50); (iv) conventional deficit irrigation (DI) at 75% of FI applied on both sides of the root zone (DI 75); and (v) DI at 50% of FI (DI 50). Among the different irrigation scenarios, the PRD 75 treatment led to the lowest level of salinity for the surface soil layer. The PRD reduced TN in the soil compared with DI, while the water source significantly increased soil TN and TC with RW by 4% and 7%, respectively, compared with FW under FI. However, the irrigation scenarios and water sources did not show significant differences in the sodium absorption ratio (SAR), but PRD could reduce SAR compared with DI when using water with a high sodium concentration, such as RW.

The importance of soil drying and re-wetting in crop phytohormonal and nutritional responses to deficit irrigation.

Soil drying and re-wetting (DRW) occurs at varying frequencies and intensities during crop production, and is deliberately used in water-saving irrigation techniques that aim to enhance crop water use efficiency. Soil drying not only limits root water uptake which can (but not always) perturb shoot water status, but also alters root synthesis of phytohormones and their transport to shoots to regulate leaf growth and gas exchange. Re-wetting the soil rapidly restores leaf water potential and leaf growth (minutes to hours), but gas exchange recovers more slowly (hours to days), probably mediated by sustained changes in root to shoot phytohormonal signalling. Partial rootzone drying (PRD) deliberately irrigates only part of the rootzone, while the remainder is allowed to dry. Alternating these wet and dry zones (thus re-wetting dry soil) substantially improves crop yields compared with maintaining fixed wet and dry zones or conventional deficit irrigation, and modifies phytohormonal (especially abscisic acid) signalling. Alternate wetting and drying (AWD) of rice can also improve yield compared with paddy culture, and is correlated with altered phytohormonal (including cytokinin) signalling. Both PRD and AWD can improve crop nutrition, and re-wetting dry soil provokes both physical and biological changes which affect soil nutrient availability. Whether this alters crop nutrient uptake depends on competition between plant and microbes for nutrients, with the rate of re-wetting determining microbial dynamics. Nevertheless, studies that examine the effects of soil DRW on both crop nutritional and phytohormonal responses are relatively rare; thus, determining the cause(s) of enhanced crop yields under AWD and PRD remains challenging.