Response of <Emphasis Type="Italic">Sorghum bicolor</Emphasis> varieties to soil salinity for feed and food production in Karakalpakstan,Uzbekistan

Water and land salinization, caused by ill-practiced irrigation and drainage is acute and widespread in Karakalpakstan, Uzbekistan. A crop frequently grown in these marginal areas is sorghum because of its capability to adapt to saline conditions. However, the salt uptake potential of local varieties for salt-ameliorative purposes, as well as possible income-generation benefits, have not yet been studied. Therefore, field experiments on low, medium and highly saline soils were conducted using four sorghum cultivars (S. vulgare, S. cernuum, S. durra, and S. technicum). The effect of soil salinity on biomass, stover and grain yield, the baking and feed quality, and total water soluble salt (TDS) accumulation, was assessed according to varieties, plant fractions and growth phases. Results showed that S. cernuum had the highest grain yield on the low (5.13 t ha⁻¹), medium (6.05 t ha⁻¹) and highly (3.3 t ha⁻¹) saline soil. S. technicum showed the lowest growth potential under all salinity levels. TDS accumulation varied between 406 and 185 kg ha⁻¹ depending on variety, site, plant fractions and growth stage. Irrespective of the soil salinity levels and varieties, TDS was highest in stover and leaves, while highest TDS uptake, mainly chlorides and bicarbonates, occurred between booting and flowering. Baking quality of all varieties was extremely low, whereas the in-vitro feed was assessed as of medium quality. The findings indicate the scope of local sorghum varieties for phytomelioration of marginal lands in Karakalpakstan, while concurrently satisfying a wider range of rural livelihood needs.     

Improving estimates of <Emphasis Type="Italic">N</Emphasis> and <Emphasis Type="Italic">P</Emphasis> loads in irrigation water from swine manure lagoons

The implementation of nutrient management plans for confined animal feeding operations requires recording N and P loads from land-applied manure, including nutrients applied in irrigation water from manure treatment lagoons. By regulation, lagoon irrigation water nutrient records in Mississippi must be based on at least one lagoon water nutrient analysis annually. Research in Mississippi has shown that N and P levels in lagoon water, and the N:P ratio, vary significantly through the year. Nutrient estimates based on one annual analysis do not account for this variability and may overestimate or underestimate N and P loads. The present study reports an improved method to more precisely estimate N and P loads in irrigation water from swine manure lagoons. The method is based on predictable annual cycles of N and P levels in lagoon water and employs simple curve-fitting of lagoon-specific formulas derived by analyses of historical data. Similarity of curves from analyses of Mississippi lagoons and other lagoon studies suggests that the method can be applied using the often limited nutrient data for a lagoon to more precisely estimate seasonal shifts of N and P and to improve the precision of estimates for N and P in irrigation water. Although the present study focused on swine manure lagoons in the southern US, recognition that the annual N cycle in lagoon water is temperature driven, suggests that additional research incorporating temperature into future models could extend these models to other types of waste treatment lagoons and climates.     

Identification and discrimination of water stress in wheat leaves (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) by means of reflectance measurements

Available water is one of the most limiting factors in crop production. As current methods for the determination of plant water content are time-consuming and require numerous observations to characterize a field, managers could benefit from remote sensing techniques to assist in irrigation decisions and further management practices. Adoption will depend on the development of technologies, which allow real time sensing of the soil and plant water status and the discrimination of several stress factors. A greenhouse study was initiated to determine specific wavelengths and/or combinations of wavelengths indicative of water stress in wheat and to evaluate these wavelengths for discriminating water stress from other biotic stresses. Reflectance of wheat leaves from plants grown under six different water treatments ranging from 65 to 26% field capacity was determined once a week from the beginning of the fourth leaf stage until the sixth leaf stage. Reflectance measurements were performed at the fourth leaf of wheat plants with an imager (LEICA S1 Pro) under controlled light conditions. Reflectance was measured in different wavelength ranges throughout the visible and infrared spectra (380–1,300 nm). Leaf scans were evaluated within the L*a*b*-color system. Total water content of wheat leaves was calculated after the difference between total fresh and total dry weight of wheat plants. Significant reflectance changes and correlations between water status and leaf reflectance were obtained at a water content <71% and enabled the identification and quantification of water status of wheat plants. Reflectance patterns at 510₇₈₀, 540₇₈₀, 490_1,300, and 540_1,300 nm were found most suitable to describe to the water status regardless of the sampling date or growth stage. To evaluate the validity of leaf reflectance as a method for separating water stress from other biotic stresses such as nutrient deficiencies reflectance pattern of water deficient plants were compared with reflectance patterns of N, P, Mg, and Fe deficiency obtained in earlier studies by calculating the color distance ΔEab as additional reflectance parameter. ΔEab increased under different nutrient deficiencies, but remained constant under water stress, thus enabling the discrimination of the investigated stress factors. The approach indicated that various stress factors could be clearly identified by reflectance measurements, thus enhancing a better plant management by the use of remote sensing techniques.     

Plant water parameters and the remote sensing <Emphasis Type="Italic">R</Emphasis><Subscript>1300</Subscript>/<Emphasis Type="Italic">R</Emphasis><Subscript>1450</Subscript> leaf water index: controlled condition dynamics during the development of water deficit stress

Plants with different abilities for osmotic adjustment (cowpea, bean, and sugarbeet) were subjected to gradually decreasing soil water content. During the development of water deficit stress, various plant water parameters were measured to characterize their relationship to the near infrared R ₁₃₀₀/R ₁₄₅₀ leaf water index, which is based on the measurement of light reflected from leaves. In all three species, leaf water thickness (LWT), leaf cell relative water content (RWC), and overall leaf thickness remained relatively constant under moderate water deficit stress. However, at the point when plants could no longer cope with the increasing level of water deficit stress, LWT, RWC, and leaf thickness were found to decrease substantially, signaling the onset of leaf dehydration. The R ₁₃₀₀/R ₁₄₅₀ leaf water index followed the RWC very closely in cowpea and bean leaves, and with some time lag in sugarbeet leaves. The R ₁₃₀₀/R ₁₄₅₀ index may therefore be used as a feedback-signal in precision irrigation control, signaling effectively the physiological response of plants when water deficit stress becomes detrimental. RWC and the R ₁₃₀₀/R ₁₄₅₀ index were linearly correlated in cowpea and bean leaves, but not in sugarbeet leaves.     

Wind effects on solid set sprinkler irrigation depth and yield of maize (<Emphasis Type="Italic">Zea mays</Emphasis>)

A field experiment was performed to study the effect of the space and time variability of water application on maize (Zea mays) yield when irrigated by a solid set sprinkler system. A solid set sprinkler irrigation layout, typical of the new irrigation developments in the Ebro basin of Spain, was considered. Analyses were performed (1) to study the variability of the water application depth in each irrigation event and in the seasonal irrigation and (2) to relate the spatial variability in crop yield to the variability of the applied irrigation and to the soil physical properties. The results of this research showed that a significant part of the variability in the Christiansen coefficient of uniformity (CU), and wind drift and evaporation losses were explained by the wind speed alone. Seasonal irrigation uniformity (CU of 88%) was higher than the average uniformity of the individual irrigation events (CU of 80%). The uniformity of soil water recharge was lower than the irrigation uniformity, and the relationship between both variables was statistically significant. Results indicated that grain yield variability was partly dictated by the water deficit resulting from the non-uniformity of water distribution during the crop season. The spatial variability of irrigation water depth when the wind speed was higher than 2 m s^–1 was correlated with the spatial variability of grain yield, indicating that a proper selection of the wind conditions is required in order to attain high yield in sprinkler-irrigated maize.     

Comparative effects of partial root-zone drying and deficit irrigation on nitrogen uptake in potatoes (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.)

The effects of partial root-zone drying (PRD) as compared with deficit irrigation (DI) and full irrigation (FI) on nitrogen (N) uptake and partitioning in potato (Solanum tuberosum L.) were investigated. Potato plants were grown in split-root pots and were exposed to FI, PRD, and DI treatments at tuber bulking stage. Just before onset of the irrigation treatment, each plant received 0.6 g N (in the form of urea) with 5% of which was ¹⁵N-labeled. After 4 weeks of irrigation treatments (i.e., one drying/wetting cycles completed in the PRD treatment), the plants were harvested and plant dry mass and N content were determined. The results showed that although the plant dry mass was not affected by the irrigation treatments, due to a reduced water use by the plant, both the PRD and DI treatments significantly increased crop water use efficiency. Compared with the FI and DI plants, PRD plants had significantly higher N contents in the leaves, stems and tubers; whereas, the ¹⁵N content in the plant organs was similar for the FI, PRD, and DI plants. It is suggested that not the root N uptake efficiency but the soil N availability was enhanced by the PRD treatment.     

Yield,quality and profitability of sensor-controlled irrigation: a case study of snapdragon (<Emphasis Type="Italic">Antirrhinum majus</Emphasis> L.) production

Advanced wireless irrigation sensor networks that can monitor and control irrigation are only recently available commercially, but on-farm research has found a number of advantages compared with current irrigation practices including reduced water application, disease incidence, production time and labor, together with increased profitability. We examined the effects of wireless sensor networks to precisely control irrigation based on substrate moisture in a 0.15-ha greenhouse producing cut-flower snapdragons (Antirrhinum majus). We calculated changes in yield, production time, quality, cost, revenue and profit using grower data on production, expenditures and sales, which included 3 years of data before and after implementation of sensor irrigation networks. Sensor-based irrigation was associated with a 62 % ($65,173 or $434,487 ha^?1) increase in revenue and a 65 % ($35,327 or $325,513 ha^?1) increase in profit per year. Sensor-based irrigation was also associated with increases in the quality and the number of stems harvested per crop. The time to first harvest and time to last harvest were reduced for all cultivar groups, indicating that the plants grew faster using sensor networks. Production time per crop was decreased, allowing 2.5 additional crops per year. Electricity usage was also reduced, likely due to less frequent irrigation using sensor networks. These results are in line with other benefits we have seen by installing sensor networks in other types of ornamental operations.     

Influence of mulching and irrigation scheduling on productivity and water use of turmeric (<Emphasis Type="Italic">Curcuma longa</Emphasis> L.) in north-western India

A field experiment was conducted to compute the water use and productivity of turmeric as a function of straw mulching and irrigation scheduling at Punjab Agricultural University, Ludhiana, during 2013 and 2014. The experiment was laid out in split plot design, keeping mulch levels (no mulch and straw mulch 6 t/ha) and irrigation methods (drip and check basin) in main plots and irrigation schedules at 0.6, 0.8, 1.0 and 1.2 irrigation water/cumulative pan evaporation (IW/CPE) in subplots. Turmeric yield was 125.2 % higher with mulching than no mulch with 50 % saving in irrigation water. Drip irrigation resulted in significantly higher turmeric yield and benefit/cost (B/C) than check basin. Irrigation scheduling at 1.2 IW/CPE recorded significantly higher turmeric yield than other schedules. Drip irrigation at 0.8 IW/CPE resulted in statistically at par yield with check basin irrigation at 1.2 IW/CPE, thus saving 40 % irrigation water with significantly higher B/C. However, turmeric yield was at par between drip irrigation at 1.2 and 1.0 IW/CPE schedule, while a significant reduction in yield was recorded in check basin at 1.0 IW/CPE compared to 1.2 IW/CPE. Turmeric should be irrigated with drip at 1.0 and with check basin at 1.2 IW/CPE to realize potential yield.     

Impact of sustained deficit irrigation on spearmint (<Emphasis Type="Italic">Mentha spicata</Emphasis> L.) biomass production,oil yield,and oil quality

Crop response to deficit irrigation is an important consideration for establishing irrigation management strategies when water supplies are limited. This study evaluated the response of native spearmint to water deficits applied using overhead sprinklers in eastern Washington, US. Five levels of irrigation were applied ranging from full irrigation (100%) to 5% of weekly averaged full crop water needs. Soil water monitoring with soil water balance was used to estimate soil water deficits for irrigation scheduling and soil water use. Mint oil yields, oil components, dry matter production, and the water-use efficiency of the spearmint were assessed. There was significant reduction in fresh mint hay (harvested biomass) yield with increasing water deficit. However, spearmint oil yields remained generally uniform across irrigation treatments at the first cutting but decreased at the driest plots during the second harvest due to a loss of plant stand. The wet harvest index and water-use efficiency improved significantly for both harvests with increasing water deficit. Hay yield, oil yield, wet harvest index, and water-use efficiency are pooled across sides and replicate blocks to provide trends with changes in maximum evapotranspiration. The three major monoterpenes show changes suggesting less mature oil yields. The study demonstrates the feasibility of sustaining native spearmint yields under managed deficit irrigations for deficits not lower than 0.5 ETc.     

Response of alfalfa (<Emphasis Type="Italic">Medicago sativa</Emphasis> L.) to diurnal and nocturnal saline sprinkler irrigations. I: total dry matter and hay quality

Little information is available on the quantitative effects on crops of saline sprinkler irrigations and the presumable beneficial effects of nocturnal versus diurnal irrigations. We measured crude protein content, carbon isotope discrimination and total dry matter (TDM) of alfalfa (Medicago sativa L.) subject to diurnal and nocturnal saline sprinkler irrigations. The work was carried out in Zaragoza (Spain) during the 2004–2006 growing seasons with a triple line source sprinkler system using synthetic saline waters dominated by NaCl with an irrigation water EC ranging from 0.5 to 5.6 dS m⁻¹. The quality of alfalfa hay assessed through its crude protein concentration was not significantly affected by salinity. Carbon isotope discrimination, an indicator of the effect of osmotic stress on plant water status, tended to decrease with increases in salinity. Based on a piecewise linear response model, alfalfa grown under saline sprinkler irrigation was shown to be more tolerant (threshold soil salinity, EC_e = 3.5 dS m⁻¹) than in previous experiments under surface irrigation (threshold EC_e = 2.0 dS m⁻¹) at relatively low salinity values, but became more sensitive at higher salinity values as shown by the higher absolute slope (13.4%) for sprinkler as compared to surface irrigation (7.3%). No significant differences in TDM were found between diurnal and nocturnal saline sprinkler irrigations. The recommended practice of irrigating at night for sprinkler irrigation using saline water is therefore not supported by our results in alfalfa grown under semiarid conditions.     

Response of alfalfa (<Emphasis Type="Italic">Medicago sativa</Emphasis> L.) to diurnal and nocturnal saline sprinkler irrigations. II: shoot ion content and yield relationships

When using saline waters, sprinkling irrigation at night is a recommended practice to reduce evaporation, salt absorption by the wetted leaves and its negative effects on crops. We measured shoot ion concentrations (Cl⁻, Na⁺ and K⁺) and total dry matter (TDM) in alfalfa subject to diurnal and nocturnal saline sprinkler irrigations and established potential relationships among them. The work was carried out along the 2004–2006 growing seasons using EC waters from 0.5 to 5.6 dS m⁻¹. Saline sprinkling irrigations linearly increased shoot Cl⁻ and Na⁺ and decreased shoot K⁺. Even though daytime evaporation was much higher than nigh-time, shoot ion accumulation and TDM were similar in the diurnal and nocturnal irrigations. The salinity tolerance of alfalfa decreased in year 2006 due to increases in shoot Cl⁻ and, particularly, shoot Na⁺. The lower threshold for shoot Na⁺ (276 meq kg⁻¹) than for shoot Cl⁻ (726 meq kg⁻¹) shows that alfalfa is more sensitive to Na⁺ than to Cl⁻, and that Na⁺ accumulation is the preponderant cause of alfalfa yield decline after 3 years of sprinkling with saline waters.