Evapotranspiration, crop coefficient and growth of two young pomegranate (Punica granatum L.) varieties under salt stress

Pomegranate (Punica granatum L.) is a drought-hardy crop, suited to arid and semi-arid regions, where the use of marginal water for agriculture is on the rise. The use of saline water in irrigation affects various biochemical processes. For a number of crops, yields have been shown to decrease linearly with evapotranspiration (ET) when grown in salt-stressed environments. In the case of pomegranate, little research has been conducted regarding the effect of salt stress. Our study focused on the responses of ET, crop coefficient (K_c) and growth in pomegranate irrigated with saline water. Experiments were conducted using lysimeters with two varieties of pomegranate, P. granatum L. vars. Wonderful and SP-2. The plants were grown with irrigation water having an electrical conductivity (EC_iw) of 0.8, 1.4, 3.3, 4.8 and 8 dS m⁻¹. Plants were irrigated with 120% of average lysimeter-measured ET. Seasonal variation in ET, crop coefficient (K_c) and growth were recorded. Variation in daily ET was observed 1 month after initiation of the treatments. While significant seasonal ET variation was observed for the EC-0.8 treatment, it remained more stable for the EC-8 treatment. Salinity treatment had a significant effect on both daily ET (F = 131, p < 0.01) and total ET (F = 112.68, p = 0.001). Furthermore, the electrical conductivity of the drainage water (EC_dw) in the EC-8 treatment was five times higher than that of the EC-0.8 treatment in the peak season. Fitting the relative ET (ET_r) to the Maas and Hoffman salinity yield response function showed a 10% decrease in ET per unit increase in electrical conductivity of the saturated paste extract (EC_e) with a threshold of 1 dS m⁻¹. If these parameters hold true in the case of mature pomegranate trees, the pomegranate should be listed as a moderately sensitive crop rather than a moderately tolerant one. Fitting 30-day interval ET_r data to the Maas and Hoffman salinity yield response function showed a reduction in the slope as the season progressed. Thus using a constant slope in various models is questionable when studying crop-salinity interactions. In addition, both of the varieties showed similar responses under salt stress. Moreover, the calculated value of K_c is applicable for irrigation scheduling in young pomegranate orchards using irrigation water with various salinities.     

Irrigation with brackish water under desert conditions I. Problems and solutions in production of onions (Allium cepa L.)

To identify the problems and suggest solutions for onion production under brackish water irrigation in a desert environment, a series of trials with brackish water (electrical conductivity, EC_i = 4.4 dS/m) and fresh water (EC_i = 1.2 dS/m) was conducted, using both sprinkler and drip irrigation systems.Under sprinkler irrigation with brackish water the mean electrical conductivity of the saturated soil extract ($\text{EC}$_e) was about 6.0 dS/m and the yield reduction was 60%. With drip irrigation, the $\text{EC}$_e under the drippers was about 5.0 dS/m and the yield reduction was 30%. Sprinkler irrigation affected yield through a reduction in both bulb size and bulb number per unit area. Drip irrigation affected the bulb number only. In the latter system seedling death occurred during the first 40 days following field emergence. Yield reduction was completely prevented by germinating and establishing the field with freshwater irrigation before transferring to brackish water irrigation, 45 days after sowing.With the sprinkler system, onion yield with brackish water irrigation could be increased by either increasing the sowing density or by alternating between brackish and fresh water irrigation.     

Different indices to characterize water use pattern of micro-sprinkler irrigated onion (Allium cepa L.)

The amount of water used by any crop largely depends on the extent to which the soil water depletion from the root zone is being recharged by appropriate depth of irrigation. To test this hypothesis a field study was carried out in November–March of 2002–2003 and 2003–2004 on a sandy loam (Aeric haplaquept) to quantify the effect of depth of irrigation applied through micro-sprinklers on onion (Allium cepa L.) bulb yield (BY) and water use patterns. Seven irrigation treatments consisted of six amounts of sprinkler applied water relative to compensate crop (K_c) and pan (K_p) coefficient-based predicted evapotranspiration loss from crop field (ET_p) (i) 160% of ET_p (1.6ET_p); (ii) 1.4ET_p; (iii) 1.2ET_p; (iv) 1.0ET_p; (v) 0.8ET_p; (vi) 0.6ET_p; (vii) 40 mm of surface applied water whenever cumulative pan evaporation equals to 33 mm. Water use efficiency (WUE), net evapotranspiration efficiency (WUE_ET) and irrigation water use efficiency (WUE_I) were computed. Marginal water use efficiency (MWUE) and elasticity of water productivity (EWP) of onion were calculated using the relationship between BY and measured actual evapotranspiration (ET_c). Yield increased with increasing sprinkler-applied water from 0.6 to 1.4ET_p. Relative to the yield obtained at 0.6ET_p, yield at 1.0ET_p increased by 23–25% while at 1.4ET_p it was only 3–9% greater than that at 1.0ET_p. In contrast, yield at 1.6ET_p was 9–12% less than that at 1.4ET_p. Maximum WUE (7.21 kg m⁻³) and WUE_ET (13.87 kg m⁻³) were obtained under 1.0ET_p. However, the highest WUE_I (3.83 kg m⁻³) was obtained with 1.2ET_p. The ET_c associated with the highest WUE was 20% less than that required to obtain the highest yields. This study confirmed that critical levels of ET_c needed to obtain maximum BYs, or WUE, could be obtained more precisely from the knowledge of MWUE and EWP.     

Assessing satellite-based basal crop coefficients for irrigated grapes (Vitis vinifera L.)

A combined methodology of basal crop coefficient (K_cb) derived from vegetation indices (VI) obtained from satellite images and a daily soil water balance in the root zone of the crop was proposed to accurately estimate the daily grape crop coefficient and actual evapotranspiration. The modeled values were compared with field measurements of crop evapotranspiration (ET) using an energy balance eddy-covariance flux tower and adjusted for closure using the measured Bowen ratio. A linear relation between K_cb and VI for vineyard was obtained, K_cb = 1.44 × NDVI-0.10 and K_cb = 1.79 × SAVI-0.08. The correlation of the measured crop coefficient (K_c) and modeled (K_crf) exhibits a linear tendency, K_c = 0.96K_crf, r² = 0.67. Other derived parameters such as weekly K_c and daily and weekly ET show good consistency with measurements and higher coefficients of determination. The study of the soil water balance suggests the importance of soil water storage in grapes within the La Mancha region. These results validate the use of remote sensing as a tool for the estimation of evapotranspiration of irrigated wine grapes planted on trellis systems.     

Seasonal variations in sap flow and soil evaporation in an olive (Olea europaea L.) grove under two irrigation regimes in an arid region of Argentina

The emergence of intensively managed olive plantations in arid, northwestern Argentina requires the efficient use of irrigation water. We evaluated whole tree daily transpiration and soil evaporation throughout the year to better understand the relative importance of these water use components and to calculate actual crop coefficient (Kc) values. Plots in a 7-year-old ‘Manzanilla fina’ olive grove with 23% canopy cover were either moderately (MI) or highly irrigated (HI) using the FAO method where potential evapotranspiration over grass is multiplied by a given Kc and a coefficient of reduction (Kr). The Kc values employed for the MI and HI treatments were 0.5 and 1.1, respectively, and the Kr was 0.46. Transpiration was estimated by measuring main trunk sap flow using the heat balance method for three trees per treatment. Soil evaporation was measured using six microlysimeters in one plot per treatment. Both parameters were evaluated for 7-10 consecutive days in the fall, winter, mid-spring, summer, and early fall of 2006-2007. Maximum soil evaporation was observed in the summer when maximum demand was combined with maximum surface wetted by the drips and evaporation from the inter-row occurred due to rainfall. Similarly, maximum daily transpiration was observed in mid-spring and summer. Transpiration of MI trees was 30% lower than in HI trees during the summer period. However, this difference in transpiration disappeared when values were adjusted for total leaf area per tree because leaf area was 28% less in the MI trees. Transpiration represented about 70-80% of total crop evapotranspiration (ETc) except when soil evaporation increased due to rainfall events or over-irrigation occurred. We found that daily transpiration per unit leaf area had a positive linear relationship with daily potential evapotranspiration (r² = 0.84) when considering both treatments together. But, a strong relationship was also observed between transpiration per unit leaf area and mean air temperature (r² = 0.93). Thus, it is possible to predict optimum irrigation requirements for olive groves if tree leaf area and temperature are known. Calculated crop coefficients during the growing season based on the transpiration and soil evaporation values were about 0.65-0.70 and 0.85-0.90 for the MI and HI treatments, respectively.     

Drip irrigation of tea (Camellia sinensis L.): 1. Yield and crop water productivity responses to irrigation

The effects of drip irrigation on the yield and crop water productivity responses of four tea (Camellia sinensis (L.) O. Kuntze) clones were studied four consecutive years (2003/2004-2006/2007), in a large (9 ha) field experiment comprising of six drip irrigation treatments (labelled: I₁-I₆) and four clones (TRFCA PC81, AHP S15/10, BBK35 and BBT207) planted at a spacing of 1.20 m × 0.60 m at Kibena Tea Limited (KTL), Njombe in the Southern Tanzania in a situation of limited water availability. Each clone × drip irrigation treatment combination was replicated six times in a completely randomized design with 144 net plots each with an area of 72 m². Clone TRFCA PC81 gave the highest yields (range: 5920-6850 kg dried tea ha⁻¹) followed by clones BBT207 (5010-5940 kg dried tea ha⁻¹), AHP S15/10 (4230-5450 kg dried tea ha⁻¹) and BBK35 (3410-4390 kg dried tea ha⁻¹) and drip irrigation treatment I₂ gave the highest yields, ranging from 4954 to 6072 kg dried tea ha⁻¹) compared with those from other treatments (4113-5868 kg dried tea ha⁻¹). Most of these yields exceeded those (4200 kg dried tea ha⁻¹) obtained from overhead sprinkler irrigation system in Mufindi also Southern Tanzania, and Kibena Estate itself. Results showed that drip irrigation of tea not only increased yields but also gave water saving benefits of up to 50% from application of 50% less water to remove the cumulative soil water deficit (treatment I₂), and with labour saving of 85% for irrigation. The yield of dried tea per mm depth of water applied, i.e., “the crop water productivity” for drip irrigation of clones TRFCA PC81, BBT207 and BBK35, in 2003/2004 for instance, were 9.3, 8.5 and 7.1 kg dried tea [ha mm]⁻¹, respectively. The corresponding values in 2004/2005 were 2.7, 4.5 and 2.0 kg dried tea [ha mm]⁻¹ while the yield responses from clone AHP S15/10 were linear decreasing by 1 and 1.6 kg dried tea [ha mm]⁻¹ in 2003/2004 and 2004/2005, respectively. In 2005/2006 the crop water productivity from clones TRFCA PC81, AHP S15/10, BBK35 and BBT207 were 4.5, 0.4, 5.2 and 6.9 kg dried tea [ha mm]⁻¹, respectively with quadratic yield response functions to drip irrigation depth of water application. The results are presented and recommendations and implications made for technology-transfer scaling-up for increased use by large and smallholder tea growers.     

Effects of irrigation regimes on yield and water productivity of safflower (Carthamus tinctorius L.) under Mediterranean climatic conditions

A field study was carried out in order to determine the effect of deficit irrigation regimes on grain yield and seasonal evapotranspiration of safflower (Carthamus tinctorius L.) in Thrace Region of Turkey. The field trials were conducted on a loam Entisol soil, on Dincer, the most popular variety in the research area. A randomised complete block design with three replications was used. Combination of four well-known growth stages of the plant, namely vegetative (V_a), late vegetative (V_b), flowering (F) and yield formation (Y) were considered to form a total of 16 (including rain fed) irrigation treatments. The effect of irrigation and water stress at any stage of development on grain yield per hectare and 1000 kernels weight was evaluated. Results showed that safflower was significantly affected by water stress during the sensitive late vegetative stage. The highest yield was obtained in V_aV_bFY treatment. Seasonal irrigation water use and evapotranspiration were 501 and 721 mm, respectively, for the non-stressed treatment. Safflower grain yield of this treatment was 5.22 Mg ha⁻¹ and weight of 1000 kernels was 55 g. The seasonal yield-water response factor value was 0.87. The total water use efficiency was 7.2 kg ha⁻¹ mm⁻¹. Irrigation schedule of the non-stressed treatment may be as follows: the first irrigation is at the vegetative stage, when after 40-50 days from sowing/elongation and branching stage, that is the end of May; the second irrigation is at the late vegetative stage, after 70-80 days from sowing/heading stage, that is in the middle of June; the third irrigation is at the flowering stage, approximately 50% level, that is the first half of July; and the fourth irrigation is at the yield formation stage, seed filling, that is the last week of July.     

Effect of N-enriched co-compost on transpiration efficiency and water-use efficiency of maize (Zea mays L.) under controlled irrigation

Population growth, urban expansion and economic development are increasing competition for water use between agriculture and other users. In addition, the high rate of soil degradation and declining soil moisture in the Sub-Saharan African Region have called for several crop production management and irrigation options to improve soil fertility, reduce water use by crops and produce ‘more crops per drop of water’. Notwithstanding this, considerable variations exist in the literature on water-use efficiency, WUE_cwu (economic yield per water used) for maize (Zea mays L.) across climates and soil management practices. Different views have been expressed on the effect of different rates of nitrogen (N) application on transpiration efficiency, TE (biomass produced per unit of water transpired). The objectives of the study were to assess the effect of different rates of N-enriched municipal waste co-compost and its derivatives on TE, WUE_cwu and yield of maize (Z. mays L.) in comparison to inorganic fertiliser. The greenhouse pot experiment was conducted in Accra, Ghana on a sandy loam soil (Ferric Lixisol) using a split plot design. The main plot treatments were soil (S), dewatered faecal sludge (DFS), municipal solid waste compost (C), co-compost from municipal solid waste and dewatered faecal sludge (Co), compost enriched with (NH₄)₂SO₄ (EC), co-compost enriched with (NH₄)₂SO₄ (ECO), (NH₄)₂SO₄ and NPK15-15-15 + (NH₄)₂SO₄. The sub-plot treatments were different rates of application of nitrogen fertiliser applied at the rate of 91, 150 and 210 kg N ha⁻¹ respectively. Maize cv. Abelehii was grown in a poly bag filled with 15 kg soil. Eight plants per treatment were selected randomly and used for the collection of data on growth parameters forth-nightly. At physiological maturity two plants per treatment were also selected randomly from each treatment plot for yield data. The results showed that TE of maize (Z. mays) varied for the different treatments and these are 6.9 Pa in soil (S) alone to 8.6 Pa in ECO. Increase in N application rate increased TE at the vegetative phase for fast nutrient releasing fertilisers (DFS, ECO, EC, NPK + (NH₄)₂SO₄, (NH₄)₂SO₄) and at the reproductive phase for slow nutrient releasing fertilisers (C and CO). Water-use efficiency increased significantly as rate of N application increased. Treatment ECO improved crop WUE_cwu and was 11% and 4 times higher than that for NPK + (NH₄)₂SO₄ or soil alone; and 18-36% higher than those for DFS and CO. Treatment ECO used less amount of water to produce dry matter yield (DMY) and grain yield (GY) that was 5.2% and 12.6%, respectively, higher than NPK + (NH₄)₂SO₄. Similarly, the DMY and GY for ECO was 8.9-18.5% and 23.4-34.7%, respectively, higher than DFS and CO. High nutrient (N and K) uptake, TE, and low leaf senescence accounts for 83% of the variations in DMY whereas WUE_cwu accounts for 99% of the variations in GY. Thus, the study concluded that different sources of fertiliser increased TE and WUE_cwu of maize differently as N application rate increases.     

Yield and water use of eggplants (Solanum melongena L.) under full and deficit irrigation regimes

Field experiments were conducted in 2008 and 2009 to determine the effects of deficit irrigation on yield and water use of field grown eggplants. A total of 8 irrigation treatments (four each year), which received different amounts of irrigation water, were evaluated. In 2008, deficit irrigation was applied at full vegetative growth (WS-V), pre-flowering (WS-F) and fruit ripening (WS-R), while in 2009 deficit irrigation was applied during the whole growing season at 80 (WS-80), 60 (WS-60) and 40% (WS-40) of field capacity. Deficit-irrigated treatments were in both years compared to a well irrigated control. Regular readings of soil water content (SWC) in 2008 and 2009 showed that average soil water deficit (SWD) in the control was around 30% of total available water (TAW) while in deficit-irrigated treatments it varied between 50 and 75% of TAW. In 2008, deficit irrigation reduced fruit fresh yield by 35, 25 and 33% in WS-V, WS-F and WS-R treatments, respectively, when compared to the control (33.0 t ha⁻¹). However, the reduction in fresh yield in response to deficit irrigation was compensated by an increase in fruit mean weight. Results obtained in 2009 showed that fruit fresh yield in the control was 33.7 t ha⁻¹, while it was 12, 39 and 60% less in WS-80, WS-60 and WS-40 treatments, respectively. On the other hand, fruit dry matter content and water productivity were found to increase significantly in both years in deficit-irrigated treatments. Applying deficit irrigation for 2 weeks prior to flowering (WS-F) resulted in water saving of the same magnitude of the WS-80 treatment, with the least yield reduction, making more water available to irrigate other crops, and thereby considered optimal strategies for drip-irrigated eggplants in the semi-arid climate of the central Bekaa Valley of Lebanon.     

Forage quality, water use and nitrogen utilization efficiencies of pearl millet (Pennisetum americanum L.) grown under different soil moisture and nitrogen levels

The increasing scarcity of water for irrigation is becoming the most important problem for producing forage in all arid and semi-arid regions. Pearl millet is a key crop in these regions which needs relatively less water than other crops. In this research, a field study was conducted to identify the best combination of irrigation and nitrogen (N) management to achieve acceptable pearl millet forage both in quantity and quality aspects. Pearl millet was subjected to four irrigation treatments with interaction of N fertilizer (0, 75, 150 and 225 kg ha⁻¹). The irrigation treatments were 40%, 60%, 80% and 100% of total available soil water (I₄₀, I₆₀, I₈₀ and I₁₀₀, respectively). The results showed that increasing moisture stress (from I₄₀ to I₁₀₀) resulted in progressively less total dry matter (TDM), leaf area index (LAI), and nitrogen utilization efficiency (NUzE), while water use efficiency (WUE) and the percentage of crude protein (CP%) increased. The highest TDM and LAI were found to be 21.45 t ha⁻¹ and 8.65, in I₄₀ treatment, respectively. TDM, WUE, CP% and profit responses to N rates were positive. The maximum WUE of 4.19 kg DM/m³ was achieved at I₁₀₀ with 150 kg N ha⁻¹. The results of this research indicate that the maximum profit of forage production was obtained in plots which were fully irrigated (I₄₀) and received 225 kg N ha⁻¹. However, in the situation which water is often limited and not available, application of 150 kg N ha⁻¹ can produce high forage quality and guaranty acceptable benefits for farmers.