Walter Zegada-Lizarazu

Deep Root Water Uptake Ability and Water Use Efficiency of Pearl Millet in Comparison to Other Millet Species

Abstract Pearl millet is better adapted to hot and semi-arid conditions than most other major cereals. The objective of this study was to compare the deep water uptake ability and water use efficiency (WUE) of pearl millet among millet species. First, the WUE of six millet species was evaluated in pots under waterlogging, well-watered (control), and drought conditions. Secondly, the water uptake from deep soil layers by pearl millet and barnyard millet, which showed the highest drought and waterlogging tolerance, respectively, was compared in long tubes which consisted of three parts (two loose soil layers separated by a hardpan and a Vaseline layer). Soil moisture was adjusted to well-watered and drought conditions in the upper (topsoil) layer, while the lower (deep) layer was always kept wet. WUE was significantly reduced in all millet species by waterlogging but not by drought. The ratio of WUE to the control condition indicated that pearl millet had the highest and lowest resistances to drought and waterlogging conditions, respectively, while barnyard millet was the most stable under both conditions. The deuterium concentration in xylem sap water, relative water uptake from deep soil layers, and water uptake efficiency of deep roots were significantly increased in barnyard millet but not in pearl millet by drought in topsoil layers. In conclusion, the drought resistance of pearl millet is explained by higher WUE but not by increased water uptake efficiency in deep soil layers as compared to barnyard millet, another drought-resistant millet species.

Water Competition of Intercropped Pearl Millet with Cowpea under Drought and Soil Compaction Stresses

Abstract Intercropping pearl millet with cowpea is a common practice in semiarid areas. Under limited water environments, competition for soil water between intercropped plants may be strong. Furthermore, the increasing soil compaction problems, due to the use of heavy machinery, may intensify competition for limited resources, particularly in the topsoil. Two field trials were conducted to evaluate the water competition ability of intercropped pearl millet when subjected to drought and soil compaction during the 2004 Japanese summer. For this purpose plant water sources were determined by the hydrogen stable isotope (deuterium) technique. Plant water relations and biomass production were also evaluated. According to the deuterium concentration values in xylem sap, pearl millet water sources were changed by the competition with cowpea. Pearl millet was forced to rely more on recently supplied (irrigation/rainfall) water. In contrast, the water sources of cowpea were unchanged by plant competition. When plants were subjected to drought, the transpiration rate of pearl millet was reduced by 40 % of its monocropped potential by competition, but that of cowpea was not. Moreover, intercropped pearl millet, under drought and soil compaction, showed lower leaf water potential and biomass than their respective monocropped counterparts. Cowpea had a higher competitive ratio under wet, dry, and compaction treatments, while pearl millet was more competitive under loose conditions. In conclusion, under drought and soil compaction, water competition restricted the water use of intercropped pearl millet, forcing pearl millet to shift to the recently supplied water. In contrast, cowpea did not show any significant changes under these stress conditions.

Hydrogen Stable Isotope Analysis of Water Acquisition Ability of Deep Roots and Hydraulic Lift in Sixteen Food Crop Species

Abstract Deep root penetration, which allows access to deep soil water and hydraulic lift, may help plants to overcome drought stress. The aim of this study was to evaluate the ability of sixteen food crop species to take up water from deep soil layers and the extent of hydraulic lift by the use of deuterated water. Plants were grown in pots consisting of two loose soil layers separated by a hardpan and a Vaseline layer. The lower (deep) layers were always kept wet (32%; ψ = –5 kPa), while soil moisture in the upper (topsoil) ones was adjusted to 25% (ψ = –7 kPa) and 12% (ψ = –120 kPa) in the well-watered and drought treatments, respectively. The deuterium labeling of the deep soil water provided evidence that wheat, Job’s tears, finger millet, soybean, barnyard millet, rice, and rye (in decreasing order of D2O increments) extracted more water from the deep layers under drought than well-watered in topsoil. These species showed significantly greater hydraulic lift under drought, except for soybean. Most of these species also showed increased root length density in deep soil layers and sustained high photosynthetic rates under drought. In contrast, pigeon pea, cowpea, common millet, pearl millet, foxtail millet, maize, barley, and oat did not show a significant increment in either deep-water uptake or hydraulic lift under drought. In summary, increased extraction of deep soil water under drought was closely related with the magnitude of hydraulic lift.

No-Tillage Enhanced the Dependence on Surface Irrigation Water in Wheat and Soybean

Abstract No-tillage often affects crop root development due to the higher mechanical impedance to root elongation, resulting in yield reduction under an unfavorable rainfall pattern, such as drought. In this study, we analyzed the changes in water source of wheat and soybean under drought stress in a continuous no-tillage field. Deuterium-labeled irrigation water was applied at different growth stages of crops to analyze their water uptake pattern. Mechanical impedance of the surface soil was 3.5 and 4.4 times higher in the no-tillage than in the conventional tillage under wet and drought conditions, respectively. Root length density and root branching index (the length of lateral roots per unit axile root length) of soybean in the surface soil layer were higher in the no-tillage field. This indicates that the increased branching by the higher mechanical impedance of undisturbed surface soil causes roots to accumulate in the surface soil layer. The deuterium concentration in the xylem sap of both crops was significantly higher in the no-tillage than in the tillage under a drought condition. This indicates that the crops in the no-tillage field depend highly on the newly supplied easily accessible water (irrigation water and/or rainfall) as compared with those in the conventional tillage field under a limited water supply. In conclusion, enhanced surface root growth in the no-tillage condition would result in higher dependence on surface supplied irrigation water than in the conventional tillage under drought.

Productivity and water source of intercropped wheat and rice in a direct-sown sequential cropping system : The effects of no-tillage and drought

Abstract In Japan, wheat-rice crop rotation with the practice of rice transplanting has been quite popular in the past. Mechanized direct-planted wheat-rice sequential cropping was developed at the Aichi Prefecture Agricultural Research Center by intercropping them for two months in spring. An objective of this study was to evaluate the introduction of continuous no-tillage to the cropping system with emphasis on water stress. The water source of intercropped wheat was also elucidated using deuterated heavy water to analyze water competition between crops. Continuous no-tillage of wheat-rice direct planting was performed for six seasons (three years) in an experimental small paddy field. No-tillage resulted in a doubled soil penetration resistance in the surface layer of soil, indicating the risk of suppressing root development. The higher yield of wheat in the dry plot suggested that excess-moisture stress occurs in the field. In the no-tillage plot, light transmission to intercropped rice seedlings increased significantly due to the reduced wheat biomass production. Wheat and rice yields were not statistically lowered by the no-tillage practice. This indicated that it is possible to introduce continuous no-tillage to the cropping system. The no-tillage significantly increased the deuterium concentrations in the xylem sap in wheat after the application of simulated rainfall with deuterated water. This indicated that the water uptake dependency of wheat shifted from stored soil water to recently applied water, which suggested the higher competition between the crops may occur under no-tillage conditions.

Pearl Millet Developed Deep Roots and Changed Water Sources by Competition with Intercropped Cowpea in the Semiarid Environment of Northern Namibia

abstract The practice of intercropping pearl millet with cowpea is widespread among subsistence farmers in northern Namibia. In this region, the scarce and erratic rainfall may enhance competition for the limited soil water between intercropped plants. Trials were conducted on a field of the University of Namibia (on-station) and on a farmer’s field (off-station) to determine the effects of competition between pearl millet and cowpea on the water sources and plant growth of each crop. The deuterium analysis showed that pearl millet, intercropped with cowpea, significantly increased its dependence on the recently supplied labeled irrigation water. Intercropped cowpea also showed an increased trend of the dependence but it was not statistically significant. At the university field, intercropped pearl millet showed higher dependence on the irrigation water than monocropped pearl millet. At the farmer’s field, the dependence of intercropped pearl millet on the irrigation water was low in the pearl millet-dominant zone. In contrast, the dependence on the irrigation water was high in the cowpea-dominant zone, indicating that the dependence on the irrigation water changes according to the size of the pearl millet canopy. The water sources of cowpea did not show a significant difference at either pearl millet-dominant or cowpea-dominant zone, indicating a stable water uptake trend under competitive conditions. Competition with cowpea significantly increased the root-weight density of intercropped pearl millet in the deep soil layers, but decreased that in the shallow layers. The root-weight density of intercropped cowpea, however, was reduced in most of the soil layers. In conclusion, cowpea has a higher ability to acquire existing soil water, forcing pearl millet to develop deep roots and shift to the surface irrigation water.

Water Acquisition From The Seasonal Wetland and Root Development of Pearl Millet Intercropped With Cowpea in A Flooding Ecosystem of Northern Namibia

Abstract Seasonal Wetlands, Locally Called Oshanas, Are Characteristic of The Densely Populated Northern Namibia, A Desert Country in Southwest Africa. The Formation of Seasonal Wetlands, Which Will Sustain The Water Balance of A Semiarid Environment, Was Quite Unstable Depending Entirely On The Variable Rainfall in The Upper Catchments of Angola. The Objective of The Present Study Was To Evaluate The Use of Seasonal Wetland Water By Pearl Millet, The Local Staple Food Crop intercropped With Cowpea, To Discuss The Water Competition Pattern of intercropped Species. Root System Development of The intercropped Species Was Also Evaluated Together With The Water Source Analysis. For This Purpose, Field Experiments Using Pearl Millet intercropped With Cowpea in The Seasonal Wetland in Namibia University (Exp. 1) and Monocropped Pearl Millet in The Local Farmers Field (Exp. 2) Were Conducted in Northern Namibia. Both Pearl Millet and Cowpea Developed Deeper Root Systems As The Distance From The Seasonal Wetland Water increased. At Flowering Time, The δD Value of intercropped Cowpea Was Similar To That of Wetland Water, While That in Pearl Millet Was Much Lower Than Those of Both The Wetland Water and Groundwater. This indicated That intercropped Pearl Millet Did Not Have Full Access To The Wetland Water When There Was Competition With Cowpea For Water Derived From Various Water Sources. Under Such Circumstances, intercropped Pearl Millet Probably Relies More On The Rainfall Water, Which Is Just Sufficient To Sustain Its Growth in A Semiarid Environment. By Contrast, intercropped Cowpea Wins in The Competition With Pearl Millet and Can Acquire Water From The Existing Stored Wetland Water.

Mixed planting with legumes modified the water source and water use of pearl millet

Abstract In semi-arid areas, pearl millet is an important staple food crop that is traditionally intercropped with cowpea. This study evaluated the water competition between pearl millet and cowpea using deuterated water. At vegetative stage, pearl millet biomass production was lower in the pearl millet-cowpea (PM-CP) combination than in the pearl millet-pigeon pea (PM-PP) and pearl millet-bambara nut (PM-BN) combinations. PM-CP used more water than PM-PP and PM-BN under well-watered conditions; however, all combinations used similar amounts of water under dry conditions. The biomass production, photosynthetic rates, transpiration rates, and midday leaf water potential of pearl millet at early flowering stage were not significantly reduced by mixed planting with cowpea sown two weeks later as compared with single planted pearl millet. When pearl millet and cowpea were sown at the same time, mix planting significantly increased the recovery rates of recently irrigated heavy water in pearl millet, but not in cowpea in both vegetative and early flowering stages. Midday leaf water potential and transpiration rates in pearl millet were lowered by mixed planting but those in cowpea were not. These indicate that the water source of pearl millet is shifted to the recently irrigated and easily accessible water. By contrast, when cowpea was sown two weeks later than pearl millet, this trend was not observed. These results provide new evidence on water competition in the PM-CP intercropping system; cowpea has higher ability to acquire existing soil water than pearl millet when both crops are sown at the same time.

The effects of the degree of soil cover with an impervious sheet on the establishment of tree seedlings in an arid environment

Low precipitation and high evaporation rates hinder the establishment of tree seedlings in arid environments. The objective of this study was to assess the effect of covering different fractions (0, 30, 70 and 100%) of the wetted area surrounding seedlings of Acacia saligna (Labill.) H.L. Wendl. with a black polyethylene sheet on the seedlings development and water use. The cover treatments were applied to plots with and without Acacia seedlings. Within the mulched areas at all depths, soil temperatures close to the edges were lower than at the corresponding depth close to the center, but still higher than in the non-mulched plots. In plots with Acacia seedlings, the total soil water losses were similar among treatments. However, the cumulative evaporative losses near the soil surface were lower with larger mulched areas. During early growth stages, roots grew deeper in the 30% mulch treatment and more laterally in the other mulched treatments. The non-mulched treatment produced the smallest root system. Larger canopies developed in the mulched treatments and the gross water use efficiency increased with the increasing fraction of the mulched area. Optimum utilization of stored soil water and seedling development were attained with the 70% mulch treatment.

Differential characteristics of photochemical acclimation to cold in two contrasting sweet sorghum hybrids.

Sweet sorghum has a photosynthetic system which is highly sensitive to cold stress and hence strongly limits its development in temperate environments; therefore, the identification of key exploitable cold tolerance traits is imperative. From a preliminary field trial, two dissimilar sweet sorghum hybrids (ICSSH31 and Bulldozer), in terms of early vigor and productivity, were selected for a controlled-environment trial aiming at identifying useful traits related to acclimation mechanisms to cold stress. The higher cold tolerance of Bulldozer was partially related to a more efficient photochemical regulation mechanism of the incoming light energy: the higher tolerance of photosystem II (PSII) to photo-inactivation was because of a more effective dissipation capacity of the excess of energy and to a more balanced diversion of the absorbed energy into alternative energy sinks. ICSSH31 increased the dissipation and accumulation of a large amount of xanthophylls, as in Bulldozer, but, at the same time, inactivated the oxygen evolving complex and the re-synthesis of chlorophyll (Chl) a and b, thus, leading to an overproduction of CO2 fixation enzymes after re-warming. In summary, in Bulldozer, the acclimation adjustments of the photosynthetic apparatus occurred through an efficient control of energy transfer toward the reaction centers, and this likely allowed a more successful seedling establishment; ICSSH31, conversely, exhibited a fast re-synthesis of Chl pigments, which appears to divert photosynthates from dry matter accumulation. Such broad acclimation traits may constitute a source for selecting higher genetic gain traits relevant for enlarging the growing season of promising biomass sorghum ideotypes in temperate climates.