Water relations,growth, yield,and fruit quality of hot pepper under deficit irrigation and partial rootzone drying

We compared two water-saving irrigation practices, deficit irrigation (DI) and partial rootzone drying (PRD), for their effects on growth and quality of ‘Ancho St. Luis’ hot pepper (Capsicum annum L.). The treatments were: commercial irrigation (CI) considered as the control, irrigating both sides of the rootzone with half of the volume of CI considered as DI, and alternating irrigation between two sides of the rootzone with half the volume of CI at each irrigation time considered as PRD. Midday leaf water potentials of PRD and DI plants were lower by 0.15 and 0.30 MPa, respectively, than of CI plants from 130 days after sowing. Total fresh mass of fruit was reduced by 19 and 34.7% in PRD and DI, respectively, compared to CI. Fruit number per plant was reduced by more than 20% in PRD and DI compared to CI. Total dry mass of fruit was similar among the treatments. At harvest, DI fruit had 21% higher total soluble solids concentration and better colour development than other treatments. Although incidence of blossom-end rot was high in PRD and DI fruit, more than 80% of fruit from PRD was not affected. DI and PRD saved 170 and 164 l of water, respectively, compared to CI and they could be feasible irrigation strategies for hot pepper production where the benefit from saving water outweighs the decrease in total fresh mass of fruit.     

Water relations and yield of lysimeter-grown strawberries under limited irrigation

The effects of partial root-zone drying (PRD), as compared to deficit irrigation (DI) and full irrigation (FI), on strawberry (cv. Honeoye) berry yield, yield components and irrigation water use efficiency (WUE_I) were investigated in a field lysimeter under an automatic rain-out shelter. The irrigation treatments were imposed from the beginning of flowering to the end of fruit maturity. In FI the whole root zone was irrigated every second day to field capacity viz. volumetric soil water content (θ) of 20%; while in DI and PRD 60% water of FI was irrigated to either the whole or one-half of the root system, respectively, at each irrigation event. In PRD, irrigation was shifted from one side to the other side of the plants when θ of the drying side had decreased to 8–11%. Compared to FI plants, leaf water potential was significantly lower in DI and PRD plants in 3 out of 10 measurement occasions, while stomatal conductance was similar among the three treatments. Leaf area, fresh berry yield (FY), individual berry fresh weight, berry water content, and berry dry weight (DW) were significantly lower in DI and PRD plants than those of FI plants; whereas the total number of berry per plant was similar among treatments. Compared with FI, the DI and PRD treatments saved 40% of irrigation water, and this led to a 28 and 50% increase of WUE_I based on berry FY and DW, respectively, for both DI and PRD. Conclusively, under the conditions of this study PRD had no advantage compared to DI in terms of berry yield and WUE_I. DI and PRD similarly decreased berry yield and yield components and thus cannot be recommended under similar conditions.     

Comparative effects of regulated deficit irrigation (RDI) and partial root-zone drying (PRD) on growth and cell wall peroxidase activity in tomato fruits

The effects of regulated deficit irrigation (RDI) and partial root-zone drying (PRD) on tomato fruit growth and cell wall peroxidase activity in tomato exocarp were investigated in growth chamber conditions. The RDI treatment was 50% of water given to fully irrigated (FI) plants and the PRD treatment was 50% of water of FI plants applied to one half of the root system while the other half dried down, with irrigation shifted when soil water content of the dry side decreased 15–20%. RDI significantly reduced fruit diameter, though PRD reduced fresh weight while having no significant effect on fruit diameter. The activity of peroxidase was significantly higher in RDI and PRD treated plants compared to those of FI. Differences between RDI and PRD were expressed on temporal basis. In the fruits of RDI treated plants peroxidase activity began to increase in the phase when fruit growth started to decline with the peak of enzyme activity of 6.1 HRPEU g⁻¹ FW reached in the phase of mature green fruits when fruit growth rate was minimal. Increase of peroxidase activity in PRD fruits coincided with the ripening phase and the peak of enzyme activity (5.3 HRPEU g⁻¹ FW) was measured at the end of fruit ripening. These data potentially identified contrasting and different roles of tomato exocarp cell wall peroxidase in RDI and PRD treated plants. In RDI treated plants peroxidase may have a role in restricting fruit growth rate, although the increase in enzyme activity during ripening of PRD treated fruit pointed out that peroxidase may also control fruit maturation by inducing more rapid process.     

Growth,yield and water use efficiency response of greenhouse-grown hot pepper under Time-Space deficit irrigation

Greenhouse-grown hot pepper was used to investigate the effect of Time-Space deficit irrigation (TSDI), a newly developing irrigation technique based on regulated deficit irrigation (RDI) and partial rootzone drying (PRD), by measuring plant growth, yield and irrigation water use efficiency. The treatments consisted of factorial combinations of three factors, organized following an orthogonal L₉ (3)⁴ test design with four growing stages. Three irrigation strategies (conventional furrow irrigation with full-water when soil water content was lower by 80% of field capacity (F), conventional furrow irrigation with 50% of full-water (D) and alternate furrow irrigation with 50% of full-water (P)) as the main plot factor were applied to select the optimum irrigation parameter at different stages of crop development, the treatment in which irrigation water was applied to both sides of root system when soil water content was lower by 80% of field capacity during all stages was considered as control (FFFF). Water consumption showed some significant effect of irrigation treatment during the growing period of different drought stress patterns application, and therefore decreased in these treatments to a level around 54.68–70.33% of FFFF. Total dry mass was reduced by 1.17–38.66% in TSDI treatments compared to FFFF. However, the root–shoot ratio of FFFF was lower than other treatments and the differences from FFFF and other TSDI treatments were statistically significant. The highest total fresh fruit yield (19.57 T ha⁻¹) was obtained in the FFFF treatment. All deficit irrigations increased the water use efficiency of hot pepper from a minimum of 1.33% to a maximum of 54.49%. At harvest, although there was difference recorded as single fruit weight and single fruit volume were reduced under the TSDI treatments, total soluble solids concentration of fruit harvested under the water-deficit treatments were higher compared to FFFF.     

Combining cover cropping with deficit irrigation in a Mediterranean low vigor vineyard

The aim of this research was to test the effects of vineyard soil management practices combined with deficit irrigation strategies on the performance of the grapevine (Vitisvinifera L.) red variety Tempranillo. Two soil management practices (soil tillage – ST and permanent resident vegetation – RV) were combined with three deficit irrigation treatments (regulated deficit irrigation – RDI, partial rootzone drying – PRD and conventional sustained deficit irrigation – DI) during two growing cycles. Compared to ST, RV reduced soil water content during spring, inducing a significant reduction in vine vegetative growth, yield and must titratable acidity. The effects of irrigation treatments were not much pronounced. Only in the second season RDI showed a significant reduction on vine vegetative growth, yield and must titratable acidity as compared to PRD and DI whose results were similar to one another.     

Effect of partial rootzone drying on growth, gas exchange, and yield of tomato (Solanum lycopersicum L.)

Three levels of partial rootzone drying (PRD) were evaluated and compared with conventional irrigation, in terms of gas exchange, water relations, growth, yield, fruit quality, and water use efficiency in tomato (Solanum lycopersicum L.) saladette-type plants growing in pots with volcanic material and drip irrigation. There were four treatments, a control, in which available water (AW) in the whole root system was allowed to fall to 90%; PRD90-30, in which on one side of the divided root AW was allowed to fall to 90% and on the other side it was allowed to fall to 30%; PRD70-30, in which on one side of the divided root AW was allowed to fall to 70% and on the other side it was allowed to fall to 30%; PRD50-30, in which on one side of the divided root AW was allowed to fall to 50% and on the other side it was allowed to fall to 30%. When each treatment reached the desired AW level they were then irrigated. At the same time, when on one side AW reached values ≤30% irrigation was shifted to the other side. Results showed a significant decrease of leaf water potential up to 14% in PRD plants compared with control. Shoot dry weight and leaf area decreased in relation to substrate available water in PRD plants. Stomatal conductance and transpiration rate were lower, up to 31 and 18%, respectively, in plants with PRD compared with control. However, CO₂ assimilation rate was similar among treatments which along with the reduction of transpiration in PRD plants, increased instantaneous water use efficiency by 28, 25, and 33% in PRD90-30, PRD70-30, and PRD50-30 treatments, respectively, compared to control. Yield, number of fruits and fruit total soluble solids content were similar among treatments. An increase of 25% in fruit titratable acidity was reached in PRD50-30. Fruit firmness increased up to 31% in PRD treatments. PRD treatments allowed a water irrigation saving up to 46%.     

Partial rootzone drying maintains fruit quality of ‘Golden Delicious’ apples at harvest and postharvest

Partial rootzone drying (PRD) has been evaluated at harvest, but its effects on apple fruit postharvest life is little known for apples grown in semi-arid regions. The objective of this study was to test the hypothesis that water savings via PRD may affect fruit quality at harvest and postharvest-life of ‘Golden Delicious’ apples grown in a semi-arid region. The experiment was conducted from 2005 to 2007. The irrigation treatments were commercial irrigation as control (CI) and PRD. After 3 years of evaluation, fruit quality at harvest, measured as fruit weight, flesh firmness, and total soluble solids concentration, was similar between CI fruit and PRD fruit. Dry matter concentration (DMC) was higher in PRD fruit than in CI fruit in 2005. The fruit quality after 18 days storage at room temperature (13–18 °C and 51–56% relative humidity) was similar between CI fruit and PRD fruit. The DMC was the highest in PRD fruit in the 2005 and 2007 growing seasons, and tended to be higher in PRD fruit than in CI fruit in 2006. Total soluble solids concentration was ≈8.7% higher in PRD fruit than in CI fruit in 2007. Fruit weight loss was similar between treatments. This study suggests that water deficit via PRD did not damage fruit quality at harvest or after storage at room temperature. Additionally, PRD irrigation saved about 3240 m³ of water per hectare. Therefore, PRD can be recommended for commercial use in semi-arid regions and to those growers interested in either long-term storage or distant markets.     

Effects of deficit irrigation strategies on cluster microclimate for improving fruit composition of Moscatel field-grown grapevines

The grapevine plays a very important role in the economic, social and cultural sectors of many regions; however vineyards are often grown in regions under stressful conditions and thus they are vulnerable to climate change. The objective of this research was to investigate the effect of partial root-zone drying (PRD) irrigation on vine water relations, vegetative growth, plant microclimate, berry composition and yield components, compared to conventional deficit irrigation (DI, 50% ETc), full irrigation (FI, 100% of ETc) and non-irrigated vines (NI). The study was undertaken in mature ‘Moscatel’ grapevines (Vitis vinifera L.) grown in Pegões, South of Portugal. Compared to the other irrigated treatments, PRD vines showed a better microclimate at the cluster zone with higher incident photosynthetic photon flux density (PPFD). Within the more open canopies of NI and PRD treatments, berry temperatures were higher than those of denser ones (DI and FI). Compared to the conventional irrigation technique the better microclimate observed in PRD vines was a consequence of a reduction in vine growth, where lower values of leaf layer number, leaf area, canopy wideness, water shoots and shoot weight were observed. In PRD vines we observed a tendency to a development of a deeper root system, while DI and FI showed a more homogeneous root distribution throughout the different soil layers. PRD showed an improvement in berry quality with higher values of flavour precursors, and total phenols concentration without any significant yield reduction compared to DI and FI.     

Effects of different mulches and irrigation methods on root growth,nutrient uptake,water-use efficiency and yield of strawberry

Field studies were conducted for two consecutive years under sub-temperate climatic conditions at Nauni in district Solan of Himachal Pradesh (30°52′N, 77°11′E 1175 asl) on loamy sand Inceptisols to investigate the effect of different mulches (hay: HM, black polyethylene: BP) on root growth, nutrient uptake, water-use efficiency (WUE) and yield of strawberry cv. Chandler under drip (DI) and surface irrigation (SI) systems. Unmulch (UM) and rainfed treatments were kept as control. Higher soil moisture content was registered under both the mulch materials during entire crop growth period. However, it was greater under BP mulch as compare to HM. The moisture conservation increased by 2.80–12.80% under BP mulch as compared to UM. HM treatment, irrespective of irrigation method increased the minimum soil temperature (2.8–5.2 °C) and reduced the maximum soil temperature (2.7–5.8 °C) as compared to UM. BP mulch increased the minimum soil temperature from 0.4 to 2.5 °C. Application of irrigation moderated the soil (minimum 2.6 and maximum 1.4 °C) temperature. Both the mulch materials were effective in enhancing root growth, nutrient uptake, WUE and yield. Application of mulch enhanced the root growth (63%), nutrient uptake (179.20%), WUE (84.40%) and yield (343%) under DI. However, respective increase under SI was 23.60, 83.80, 109.40 and 219.20%. Under DI, 51% of irrigation water was saved and about 19% higher fruit yield was obtained as compared with SI treatment. Linear regression model could significantly describe the variations in nutrient uptake (N, P and K) and WUE of strawberry under sub-temperate climatic conditions, root mass density was better indicator for estimating nutrient uptake of strawberry.     

Effects of deficit irrigation on biomass,yield, water productivity and fruit quality of processing tomato under semi-arid Mediterranean climate conditions

Processing tomato is a high water demanding crop, thus requiring irrigation throughout growing season in arid and semiarid areas. The application of deficit irrigation (DI) strategies to this crop may greatly contribute to save irrigation water. A two-year study was carried out in order to assess the effects of DI upon water productivity, final biomass, fruit yield and some quality traits of open-field processing tomato cv. Brigade in a typical semi-arid Mediterranean environment of South Italy. Four irrigation treatments were studied: no irrigation following plant establishment (V0); 100% (V100) or 50% (V50) evapotranspiration (ETc) restoration up to fruit maturity, 100% ETc restoration up to flowering, then 50% ETc restoration (V100-50). Total dry biomass accumulation was significantly depressed by early soil water deficit in V0; irrigation at a reduced rate (50% ETc) from initial stages (V50) or from flowering onwards (V100-50) did not induce any losses in final dry biomass. The marketable yield did not significantly differ among plots irrigated, but an averaged irrigation water saving of 30.4% in V100-50 and 46.2% in V50 was allowed as compared to V100. Marketable yield was negatively affected by the early water shortage in V0, due to the high fruit losses (>44%). The effects of DI on fruit quality were generally the converse of those on fruit yield. DI improved total soluble solids content, titratable acidity and vitamin C content. Water use efficiency was positively affected by DI, suggesting that the crop does not benefits from the water when this last is supplied to fulfil total crop requirements for the whole season. Yield response factor, which indicates the level of tolerance of a crop to water stress, was 0.49 for total dry biomass (Kss) and 0.76 for marketable yield (Ky), indicating that in both cases the reduction in crop productivity is proportionally less than the relative ET deficit. In conclusion, the adoption of DI strategies where a 50% reduction of ETc restored is applied for the whole growing season or part of it could be suggested in processing tomato, to save water improving its use efficiency, minimizing fruit losses and maintaining high fruit quality levels. This aspect is quite important in semi-arid environments, where water scarcity is an increasing concern and water costs are continuously rising.     

Drying half of the root-zone from mid fruit growth to maturity in ‘Hass’ avocado (Persea americana Mill.) trees for one season reduced fruit production in two years

We tested the effect of extended drying of half the root system on fruit yield and fruit Ca concentration, an indirect measure of fruit quality, in avocado (Persea americana Mill. cv Hass). In a field experiment on a sandy soil, withholding irrigation and plastic sheeting was used to dry the root-zone beneath the whole canopy (DD) or half the canopy (WD), compared with well-watered trees (WW). The irrigation water contained added nutrients and was slightly saline. Yield, shoot growth, leaf conductance, leaf and fruit water status and mineral concentrations of leaves and fruit were studied. The responses of treated trees were assessed in the following season during which normal irrigation practices were restored. With respect to yield, the WD treatment behaved the same as the DD treatment. It reduced yield by more than half and proportionately more than the reduction in water supply thus reducing irrigation efficiency. Re-watering did not restore yield of WD or DD-trees in the next season. The WD and DD treatments had no effect on the concentration of Ca in the fruit mesocarp and so are unlikely to affect fruit quality. The main impact of reduced water supply on the trees was fruit abscission and this was linked to dry soil around the roots rather than the water status of the leaves or fruits. We conclude that extended drying of half of the root-zone in one season reduced irrigation efficiency for two seasons by promoting the abscission of developing fruit to the same extent as occurred when the whole root system was exposed to extended drying.     

Capability of the ‘Ball-Berry’ model for predicting stomatal conductance and water use efficiency of potato leaves under different irrigation regimes

The capability of the ‘Ball-Berry’ model (BB-model) in predicting stomatal conductance (g_s) and water use efficiency (WUE) of potato (Solanum tuberosum L.) leaves under different irrigation regimes was tested using data from two independent pot experiments in 2004 and 2007. Data obtained from 2004 was used for model parameterization, where measurements of midday leaf gas exchange of potted potatoes were done during progressive soil drying for 2 weeks at tuber initiation and earlier bulking stages. The measured photosynthetic rate (A_n) was used as an input for the model. To account for the effects of soil water deficits on g_s, a simple equation modifying the slope (m) based on the mean soil water potential (Ψ_s) in the soil columns was incorporated into the original BB-model. Compared with the original BB-model, the modified BB-model showed better predictability for both g_s and WUE of potato leaves on the parameterization data set. The models were then tested using the data from 2007 where plants were subjected to four irrigation regimes: non-irrigation (NI), full irrigation (FI), partial root-zone drying (PRD), and deficit irrigation (DI) for 3 weeks during tuber initiation and earlier bulking stages. The simulation results showed that the modified BB-model better simulated g_s for the NI and DI treatments than the original BB-model, whilst the two models performed equally well for predicting g_s of the FI and PRD treatments. Although both models had poor predictability for WUE (0.47 < r² < 0.71) of potato leaves, the modified BB-model was able to distinguish the effects of the irrigation regimes on WUE being that the WUE was generally greater for PRD than for FI and DI plants. Conclusively, the modified BB-model is capable of predicting g_s and of accounting for the differential effects of irrigation regimes on WUE of potato leaves. This information is valuable for further simulating potato water use thereby optimizing WUE under field conditions.     

Effects of deficit irrigation on fruit maturity and quality of ‘Braeburn’ apple

Effects of deficit irrigation (DI) on fruit maturity at harvest, ripening characteristics, and changes in fruit quality during and after storage of ‘Braeburn’ apple (Malus domestica Borkh.) were studied in two experiments. In Experiment 1, irrigation treatments were a commercially irrigated control (CI), an early deficit irrigation (EDI) applied from 63 to 118 days after full bloom (DAFB), and a late deficit irrigation (LDI) applied from 118 DAFB to final harvest on 201 DAFB. Irrigation treatments in Experiment 2 were a commercially irrigated control (CI) and a whole-season deficit irrigation (WDI). These DI treatments all reduced volumetric soil water content. The LDI and WDI advanced fruit ripening but EDI did not. All DI treatments increased fruit total soluble solids (TSS) and firmness regardless of maturity but had little or no effect on titratable acidity. The differences in TSS started during fruit growth much earlier than the onset of ripening and were maintained during and following storage at 0°C. The differences in firmness also started during fruit growth and were maintained for at least 10 weeks of storage at 0°C.     

Nitrogen and water use efficiency of zucchini squash for a plastic mulch bed system on a sandy soil

Zucchini squash (Cucurbita pepo L.) is an economically important vegetable crop in Florida. Typically, it is intensively managed with high inputs of fertiliser and irrigation water. Our objectives were to evaluate the interaction between fertilisation rates and irrigation treatments, and to quantify nitrate leaching in a plastic mulched/drip irrigated zucchini squash production systems. Three studies were carried out. The first study evaluated different depth placement of drip and fertigation lines on plant growth and fruit yield. Treatments included SUR (both irrigation and fertigation drip lines placed on the surface); S&S (both lines buried 0.15 m deep); and SDI (irrigation line placed 0.15 m below the fertigation line on the surface). The second and third studies compared three different N-rates and different soil moisture sensor-based irrigation strategies. Nitrate-N leaching was monitored by zero tension drainage lysimeters and soil samples. N leaching increased when irrigation and N-rates increased, with values ranging from 2 to 45 kg ha⁻¹ of N. Use of SDI increased yields by 16% compared to the S&S treatment, and reduced nitrate leaching by 93% while increasing the water use efficiency by 75% compared to a fixed 2-h irrigation event per day treatment. Application of N above the standard recommended rate of 145 kg ha⁻¹ did not increase yield, although yields were reduced at the lowest N-rate. The use of soil moisture sensors for automatic irrigation control reduced irrigation application and minimized nitrogen leaching. In addition, combining the soil moisture controlled SDI system that had surface applied fertigation resulted in similar or higher yields, while reducing both water use and potential N leaching because of improved nutrient retention in the root zone.     

Increasing cherry tomato yield using fish effluent as irrigation water in Northeast Brazil

The rational use of water in arid and semi-arid zones is fundamental for resource sustainability. The integration of aquaculture with agriculture appears to be an excellent way of saving water, disposing aquaculture effluents and providing additional fertilizer to the agricultural crop. The objective of this study was to test the feasibility of using fish effluent to irrigate cherry tomatoes cultured with different types of organic fertilizers. A field experiment was carried out in a randomized complete block design in a 2 × 5 factorial scheme, with four replications. The treatments consisted of the combination of two irrigation water types (well water and fish effluent) with five fertilizers (cow manure, chicken manure, vermi-compost, commercial compost and a control without fertilization). Evaluations for tomato fruit number, productivity and mean fruit weight were performed. Statistical analyses were done in the following harvest periods: 0–25, 0–50, 0–75 and 0–100% of the harvest days. On the first three harvest periods analyzed, treatments irrigated with fish effluent had higher fruit number and productivity. This effect was more evident when the organic fertilizer used did not attend all plant needs. The higher productivity observed in effluent treatments was related to the increase in fruit number. The higher productivity in treatments with fish effluent has a special importance for small farmers, to whom fertilizers are often cost prohibitive or unavailable.     

Fruit thinning in ‘Conference’ pear grown under deficit irrigation: Implications for fruit quality at harvest and after cold storage

Fruit thinning in pear is feasible for mitigation of water stress effects. However, it is not well known how fruit quality at harvest and after cold storage is affected by pre-harvest water stress. Even less is known about the effects of fruit thinning on quality under these circumstances. To elucidate these, we applied deficit irrigation (DI) and fruit thinning treatments to ‘Conference’ pear over the growing seasons of 2008 and 2009. At the onset of Stage II (80 and 67 days before harvest in 2008 and 2009, respectively), two irrigation treatments were applied: full irrigation (FI) and DI. FI trees received 100% of crop evapotranspiration (ETc). DI trees received no irrigation during the first three weeks of Stage II to induce water stress, but then received 20% of ETc to ensure tree survival. From bud-break until the onset of Stage II and during post-harvest, FI and DI trees received 100% of ETc. Each irrigation treatment received two thinning levels: no thinning leaving commercial crop load (∼180 fruits tree⁻¹), and hand-thinning at the onset of Stage II leaving a light crop load (∼85 fruits tree⁻¹). Under commercial crop loads, DI trees were moderately water-stressed and this had some positive effects on fruit quality. DI increased fruit firmness (FF), soluble solids concentrations (SSC) and acidity at harvest while no changes were observed in fruit maturity (based on ethylene production). Differences in FF and acidity at harvest between FI and DI fruit were maintained during cold storage. DI also reduced fruit weight loss during storage. But fruit size was reduced under DI. Fruit thinning under DI resulted in better fruit composition with no detrimental effect on fresh-market yield compared to un-thinned fruit. Fruit size at harvest and SSC values after five months of cold storage were higher in fruit from thinned trees than fruit from un-thinned trees. Fruit thinning increased fruit ethylene production, indicating advanced maturity. This may lead to earlier harvest which is desirable in years with impending drought. Fruit thinning is therefore a useful technique to enhance pear marketability under water shortage.     

A comparative study of young ‘Thompson Seedless’ grapevines (Vitis vinifera L.) under drip and furrow irrigation. II. Growth, water use efficiency and nitrogen partitioning

The response of 3-year-old grapevines (Vitis vinifera L. cultivar ‘Thompson Seedless’) to furrow and drip irrigation was quantified in terms of water status, growth, and water use efficiency (WUE). Drip irrigation was applied daily according to best estimates of vineyard evapotranspiration while furrow irrigations were applied when 50% of the plant available soilwater content had been depleted. Drip and furrow irrigated vines showed similar water status (midday leaf water potential, Ψ₁) and shoot growth patterns throughout the season. Dry weight partitioning was not significantly different between treatments but root mass was somewhat larger for the furrow than drip irrigated vines. Nitrogen concentrations of the fruit and roots were significantly (P < 0.05) less for the drip irrigated vines when compared with the furrow treatment. Similar WUE (kg water kg⁻¹ fresh fruit wt.) were obtained for both treatments indicating that furrow irrigation was as efficient as drip irrigation under the conditions of this study. The data indicate that drip irrigation may increase the potential for control of vine growth by making vines more dependent on irrigation and N fertilization than furrow irrigation.     

Evaluating variability of root size system and its constitutive traits in hot pepper (Capsicum annum L.) under water stress

The importance of root size system has long been recognized as crucial to cope with drought conditions. This investigation was conducted to: (i) evaluate the variability in root size system of hot pepper at maturity; (ii) estimate the effect of root size system on yield under drought conditions; and (iii) effect of water stress on xylem vessel development and total xylem cross-sectional area in roots of hot pepper cultivars. Twelve diverse hot pepper cultivars were grown in wooden boxes with two different water treatments, normal and in 50% water application as water deficit condition. Mean primary root length (PRL) showed a significant positive correlation with final fruit yield at normal as well as stressed condition. Total dry mass of fruit was reduced by 34.7% in drought treatments (DI) compared to full watered treatment (FI). At harvest, water-stressed plants had 21% lower root dry weight mass but higher root:shoot ratio other than FI. PRL, lateral root density, total xylem area per root cross-section showed a significant positive relationship with fruit yield. Also, lateral root density was higher in cultivars with higher xylem density, particularly in tolerant cultivars. Lateral root density (r = 0.847, P < 0.001) and total xylem cross-sectional area in root (r = 0.926, P < 0.001) were tightly related with total biomass production. The importance of root traits contributing to withstand drought in hot pepper is discussed.     

Root zone soil nitrogen management to maintain high tomato yields and minimum nitrogen losses to the environment

Greenhouse field experiments on tomato were carried out at Shouguang, Shandong province, over four double cropping seasons between 2004 and 2008 in order to understand the effects of manipulating root zone N management (RN) on fruit yields, N savings and N losses under conventional furrow irrigation. About 72% of the chemical N fertilizer used in conventional treatment (CN) inputs could be saved using the RN treatment without loss of yield. The cumulative fruit yields were significantly higher in the RN treatment than in the CN treatment. Average seasonal N from irrigation water (118 kg N ha⁻¹), about 59% of shoot N uptake, was the main nitrogen source in treatments with organic manure application (MN) and without organic manure or nitrogen fertilizer (NN). N losses in the RN treatment were lowered by 54% compared with the CN treatment. Lower N losses were found in the MN and NN treatments due to excessive inputs of organic manure and fruit yields were consequently substantially affected in the NN treatment. The critical threshold of N_min supply level in the root zone (0–30 cm) should be around 150 kg N ha⁻¹ for sustainable production. April to May in the winter–spring season and September to October in the autumn–winter season are the critical periods for root zone N manipulation during crop growth. However, control of organic manure inputs is another key factor to further reduce surplus N in the future.     

Effects of oxygen-enriched nutrient solution on greenhouse cucumber and pepper production

A series of experiments were conducted with greenhouse cucumber and pepper plants to determine the effects of oxygen enrichment of the irrigation water on yield and fruit shelf-life. The experiments were carried out in soilless culture in research greenhouses. Depending on the experiment, treatments included sub-ambient (2 mg L⁻¹), ambient (5–6 mg L⁻¹), medium (16 mg L⁻¹) and high (30–40 mg L⁻¹) levels of oxygen in the supply tank. Cucumber plants were grown in yellow cedar sawdust and pepper plants in either sawdust or perlite. Oxygen enrichment resulted in a promotion of cucumber yield in only one experiment; in two other experiments, none of the oxygen treatments, including those at sub-ambient levels, had an effect. There were no effects of oxygen enrichment on pepper yield. However, in both cucumber and pepper, fruit shelf-life was extended in oxygen-enriched treatments. In terms of system efficacy, oxygen levels in the irrigation water were measured at the dripper and found to decrease by 20–67% of initial values compared to the supply tank values, depending on the initial oxygen concentration and on the experiment. Oxygen concentrations decreased even further to virtually ambient levels when measured in the drain water or in the substrate reservoir. Cucumber plant growth was promoted under conditions which facilitated consistently high oxygen in the root zone, achieved through heavy irrigation (1 min in two) with oxygen-enriched nutrient solution of plants grown in saturated substrate (pumice). However, those extreme irrigation rates would not be practical for commercial cucumber or pepper production. Overall, this study demonstrates that oxygen enrichment of porous substrates under typical hydroponic conditions is difficult and possibly because of this, effects on yield are infrequent. However, fruit shelf-life may be improved.