Dryland Plots Research Articles

Cultivar, irrigation management, and mepiquat chloride strategy: Effects on cotton growth, maturity, yield, and fiber quality

Drought negatively affects cotton growth and yield, whereas excessive irrigation can limit yield through excessive vegetative growth and poor fruit retention. Mepiquat chloride (MC) application limits plant height, improves fruit retention and hastens maturity in responsive cultivars. Thus, the objective of this study was to address the effects of cultivar, irrigation, and MC strategy on cotton growth, maturity, yield, and fiber quality. Therefore, a field study was carried out using three cultivars, three different irrigation treatments, and three different MC treatments during the 2020 and 2021 growing seasons. In both years there was an interaction between irrigation and MC management for plant height. In 2020, MC treatments hastened cutout by two to three weeks in irrigated plots but did not affect cutout date in dryland plots. 2020 and 2021 differed substantially in rainfall (347 mm and 735 mm, respectively from planting to harvest). 2020 was a dry year in which yield responded positively to irrigation and 2021 was a wet year in which yield responded negatively to irrigation. There was no effect of MC treatments or interaction between MC and any other effect on lint yield. Fiber length was reduced, whereas strength and micronaire were increased by drought stress in 2020. Increased fiber length, strength, uniformity, and micronaire were observed by MC application in both years. Therefore, we can conclude that aggressive MC management reduces vegetative growth, promotes earlier physiological maturity under well-watered conditions, and affects fiber quality, but does not necessarily interact with irrigation management to affect lint yield. • Growth and maturity responses to mepiquat chloride depend on water availability. • Mepiquat chloride hastens maturity under water replete conditions, but not dryland. • Occasionally, fiber quality was positively impacted by mepiquat chloride application. • Mepiquat chloride did not alter cotton yield response to water excess or drought.

Economic penalties associated with irrigation during high rainfall years in the southeastern United States

Although cotton is a drought-tolerant crop, irrigation is still needed to ensure productivity, even in the humid Southeastern United States. Irrigation must be carefully managed to limit unnecessary water use while ensuring maximum economic productivity. To better understand the costs and net returns of irrigation and cultivar selection, field experiments were conducted in 2016 and 2017 to compare cotton lint yield and fiber quality in dryland plots and plots irrigated using the University of Georgia checkbook method (UGA Checkbook) at a field site near Camilla, Georgia. Results showed cultivar differences in fiber quality parameters of micronaire and uniformity in 2016, but there was no cultivar difference in fiber quality in 2017. Cultivar differences were not observed in yield or net returns for both years. However, stoplight chart analysis of net returns indicated differences in cultivar selection for irrigated or dryland production. ST 6182 GLB2 would be a better option for a producer to minimize downside risk under dryland conditions, and PHY 333 WRF would be a better option under irrigated production. Results also indicated that broadly applying simplistic water balance approaches could decrease yield, water productivity, and net returns, especially in environments where rainfall is sufficient yet unpredictable. Overirrigation affected some fiber quality parameters but did not impact the overall market price for cotton. In 2016, irrigating according to the UGA Checkbook method negatively impacted yield and net returns. In 2017, irrigation did not affect yield but negatively impacted net returns. Average losses in net returns associated with excessive irrigation in these two wet years were $336 per hectare for net return over irrigation variable costs, and $645 per hectare for net return over irrigation total costs. Implementing robust, efficient irrigation strategies is necessary to achieve high cotton yields, reduce water usage, and improve economic returns.

Response of lentil cultivars to Sclerotinia white mold and Botrytis grey mold infection under irrigated and dryland conditions

Diseases such as Sclerotinia white mold (SWM), caused by the fungus Sclerotinia sclerotiorum (Lib.) de Bary, and Botrytis grey mold (BGM), caused by the fungus Botrytis cinerea Pers., may be limiting factors for lentil production in wetter areas of Alberta, Canada. Field trials were conducted at the Lethbridge Research and Development Centre from 2013 to 2015 to evaluate the response of lentil cultivars to SWM and BGM and yield impacts. Ten lentil cultivars from five market classes were evaluated under irrigated and dryland plots with two planting densities (120 and 160 plants·m−2). Year and irrigation had the largest effect on disease incidence, with highest SWM incidence occurring under irrigation in 2013, followed by 2014 and 2015. Conversely, BGM incidence under irrigation was highest in 2015 and lowest in 2013, but levels were lower than SWM. Significantly (P < 0.05) lower disease incidences were observed in dryland plots, which also produced higher yield than irrigated plots. Cultivars varied significantly in SWM incidence and yield under irrigated and dryland conditions, perhaps due to variable disease pressure, but there was no consistent trend in cultivar performance. BGM incidence was similar in cultivars, but differed among years. These findings indicate that SWM may be a limiting factor to lentil production in wetter areas, as the 10 cultivars from five market classes tested were all highly susceptible to SWM.

Nitrogen- and phosphorus-starved Triticum aestivum show distinct belowground microbiome profiles.

Many plants have natural partnerships with microbes that can boost their nitrogen (N) and/or phosphorus (P) acquisition. To assess whether wheat may have undiscovered associations of these types, we tested if N/P-starved Triticum aestivum show microbiome profiles that are simultaneously different from those of N/P-amended plants and those of their own bulk soils. The bacterial and fungal communities of root, rhizosphere, and bulk soil samples from the Historical Dryland Plots (Lethbridge, Canada), which hold T. aestivum that is grown both under N/P fertilization and in conditions of extreme N/P-starvation, were taxonomically described and compared (bacterial 16S rRNA genes and fungal Internal Transcribed Spacers—ITS). As the list may include novel N- and/or P-providing wheat partners, we then identified all the operational taxonomic units (OTUs) that were proportionally enriched in one or more of the nutrient starvation- and plant-specific communities. These analyses revealed: a) distinct N-starvation root and rhizosphere bacterial communities that were proportionally enriched, among others, in OTUs belonging to families Enterobacteriaceae, Chitinophagaceae, Comamonadaceae, Caulobacteraceae, Cytophagaceae, Streptomycetaceae, b) distinct N-starvation root fungal communities that were proportionally enriched in OTUs belonging to taxa Lulworthia, Sordariomycetes, Apodus, Conocybe, Ascomycota, Crocicreas, c) a distinct P-starvation rhizosphere bacterial community that was proportionally enriched in an OTU belonging to genus Agrobacterium, and d) a distinct P-starvation root fungal community that was proportionally enriched in OTUs belonging to genera Parastagonospora and Phaeosphaeriopsis. Our study might have exposed wheat-microbe connections that can form the basis of novel complementary yield-boosting tools.

Long-Term Irrigation Affects the Dynamics and Activity of the Wheat Rhizosphere Microbiome.

The Inland Pacific Northwest (IPNW) encompasses 1. 6 million cropland hectares and is a major wheat-producing area in the western United States. The climate throughout the region is semi-arid, making the availability of water a significant challenge for IPNW agriculture. Much attention has been given to uncovering the effects of water stress on the physiology of wheat and the dynamics of its soilborne diseases. In contrast, the impact of soil moisture on the establishment and activity of microbial communities in the rhizosphere of dryland wheat remains poorly understood. We addressed this gap by conducting a three-year field study involving wheat grown in adjacent irrigated and dryland (rainfed) plots established in Lind, Washington State. We used deep amplicon sequencing of the V4 region of the 16S rRNA to characterize the responses of the wheat rhizosphere microbiome to overhead irrigation. We also characterized the population dynamics and activity of indigenous Phz+ rhizobacteria that produce the antibiotic phenazine-1-carboxylic acid (PCA) and contribute to the natural suppression of soilborne pathogens of wheat. Results of the study revealed that irrigation affected the Phz+ rhizobacteria adversely, which was evident from the significantly reduced plant colonization frequency, population size and levels of PCA in the field. The observed differences between irrigated and dryland plots were reproducible and amplified over the course of the study, thus identifying soil moisture as a critical abiotic factor that influences the dynamics, and activity of indigenous Phz+ communities. The three seasons of irrigation had a slight effect on the overall diversity within the rhizosphere microbiome but led to significant differences in the relative abundances of specific OTUs. In particular, irrigation differentially affected multiple groups of Bacteroidetes and Proteobacteria, including taxa with known plant growth-promoting activity. Analysis of environmental variables revealed that the separation between irrigated and dryland treatments was due to changes in the water potential (Ψm) and pH. In contrast, the temporal changes in the composition of the rhizosphere microbiome correlated with temperature and precipitation. In summary, our long-term study provides insights into how the availability of water in a semi-arid agroecosystem shapes the belowground wheat microbiome.

The Effect of Various Supplementary Irrigation Treatments on Plant and Soil Moisture Relationships in a Vineyard (Vitis Vinif era var. Chenin Blanc)

In a field plot trial with grape vines planted on a high potential soil, the soil moisture status on different irrigation treatment plots was compared with that of a dryland control. Soil moisture budgeting was based on physical soil properties and root distribution patterns before treatments commenced. A maximum concentration of roots occurred at the 300-450 mm depth zone, while approximately 90 per cent of the total number of roots was found above 900 mm. Tensiometric readings of soil moisture potential, supplemented by electrometric resistance readings from gypsum blocks, indicated complete depletion between veraison and harvesting of the total available moisture on dryland plots. Despite this severe moisture stress as illustrated by chrono-isopletes, a reasonably good grape yield was still produced by the dryland vines, indicating either exceptional drought resistance or the uptake of water from extraneous sources. Supplementary irrigations greatly improved soil moisture conditions during the important growth stages of (a) flowering and fruit set, (b) green berry stage and (c) veraison. Moisture depletion patterns changed markedly as the season progressed from November to January, and as naturally stored rain water became depleted. In contrast to the absorption pattern in November, the fastest rate of water loss occurred in the deepest root zones during January, because of unsaturated moisture flow into the dry partly decomposed parent material. The apparently unproductive subsoil might act as a large natural reservoir for superfluous winter rain, which in summer becomes available to the vines through unsaturated upward flow into the root zone. Determination of leaf water potential showed unexpectedly high values at night (minima of -283kPa) in plants growing in soil of which the major part was dried below wilting point. Vines were thus able to regain turgidity at night. Crop factors for use with the American Class A-pan for scheduling irrigations were calculated. Crop factors were low (November to February = 0,20-0,30), and again emphasised the ability of vines to use water frugally. Crop factors were strongly dependent upon soil moisture conditions. Empirical coefficients for use in the Blaney-Criddle formula are also presented.

Effect of drought stress on male fertility restoration in A3 CMS-inducing cytoplasm of sorghum

Use of cytoplasmic male sterility (CMS) in hybrid breeding requires effective male fertility-restoring lines. In sorghum, very few restoring lines that can restore fertility in A3 CMS have been reported. To identify the reasons for this deficiency, F1 and F2 hybrids of an A3 CMS line crossed with the line IS1112C, a donor of fertility-restoring (Rf) genes for A3 cytoplasm, and testcrosses of fertile plants to A3 CMS lines were grown under contrasting water availability regimes in dryland and irrigated field plots. In the irrigated plots the frequency of fertile plants in testcrosses was twice that in dryland plots (P<0.05). Fertile plants from the F2 family grown in the irrigated plots showed significantly higher restoration ability than fertile plants from the same family grown in dryland plots. F3 plants from the F2 family grown in irrigated plots yielded on average a sixfold higher frequency of fertile plants in testcrosses than F3 plants derived from dryland plots (P<0.01). Fertility of testcross hybrids correlated negatively with air vapor pressure deficit (VPD) at flowering (r=−0.96; P<0.01) suggesting that VPD is a trigger for downregulation of Rf genes for A3 cytoplasm.

Scale dependence and patch size distribution: clarifying patch patterns in Mediterranean drylands

AbstractIn drylands, the underlying vegetation structure is associated with ecosystem functioning and ecosystem resilience. Although scale‐dependent patterns are also predicted, empirical evidence often demonstrates that patch sizes are distributed according to a power‐law probability distribution function or truncated power‐law probability distribution function for a varied range of environmental conditions. Using satellite images and field measures, we assessed the spatial pattern of vegetation patches for a wide range of vegetation cover values in a large set of Mediterranean dryland (MDL) plots, focusing on the statistical distribution function that better fits the patch sizes. We found that power‐law or truncated power‐law probability distribution function does not always fit the observed patch size frequencies, while lognormal probability density function always fit well to them, implying that the vegetation structure is scale dependent for a large range of conditions. We show how the sampling approach, fit methods, and system dimensionality can affect the patch size distribution, which can explain some conflicting evidence obtained from the empirical data. Our findings question the robustness of criticality as the underlying mechanism driving vegetation patterns in MDLs. The better fit to patch size distribution provided by lognormal as compared with power‐law indicates that multiplicative effects of multivariate local influences underlie pattern formation, and suggests that the role of plant–plant facilitation can be overestimated for a large range of conditions.

LAND TENURE SECURITY ISSUES IN SMALLHOLDER IRRIGATION SCHEMES IN ZIMBABWE

The main objective of the study was to examine land tenure practices and their implications on the sustainability of the smallholder irrigation schemes in Zimbabwe. The different phases of land reforms in Zimbabwe have not been focusing on community irrigation schemes and the evolution of land rights. The farmers’ ownership feelings were stronger for their dryland plots than they were on irrigation plots as the irrigation schemes were regarded as an off-farm employment while their dry-land plots were regarded as transgenerational family assets. Farmers had different perceptions about the security of tenure, inheritability, subletting and disposal of the irrigation plots. The differences in tenure practices and perception attested to the absence of land policy for community irrigation schemes. The existence of informal land markets in some schemes and their absence in others affirmed the Market for the Poor (M4P) assertion that where formal rules and their application are weak, the business environment is governed by the informal rules and the absence of both formalrules and informal institutions make the environment for markets dysfunctional. Some farmers felt theirrigation plots should remain state owned to allow smooth running of schemes and management of farmers’ group dynamics of the irrigation. Some, however, felt the irrigation plots should be privately owned in order to allow farmers to invest and to access financial and input markets.Â

Disease Severity and Microsclerotium Properties of the Sorghum Sooty Stripe Pathogen, Ramulispora sorghi

Ramulispora sorghi causes sooty stripe of sorghum. Disease severity in irrigated and dryland plots was measured for 25 susceptible sorghum genotypes during the 2007 and 2008 growing seasons using a rating scale based upon percent leaf area infected. Disease severity ratings were approximately 1.4 points higher (P < 0.0001) on the rating scale in the irrigated plots than dryland plots for 2007 and 2008. Sooty stripe lesions were collected from each sorghum genotype in irrigated plots and assessed for mean microsclerotium production within lesions, microsclerotium size, and sporogenic germination, with significant differences apparent between genotypes for microsclerotium size (P = 0.01) and sporogenic germination (P = 0.01). There was no relationship between disease severity and microsclerotium production within leaf lesions, microsclerotium size, or sporogenic germination; however, there was a positive and significant correlation between microsclerotia production within a lesion and microsclerotium size (R2 = 0.19, P < 0.0001). Although microsclerotia from sorghum lesions varied in structural characteristics and their ability to produce spore masses, these qualities were dependent upon the sorghum genotype from which the microsclerotia were derived, because the R. sorghi population was genetically uniform as determined by internal transcribed spacer sequences and random amplified polymorphic DNA polymerase chain reaction.

Land-use intensification in New Zealand: effects on soil properties and pasture production

SUMMARYLand-use intensification requires more farm inputs to sustain or increase farm product outputs. However, a common concern for land-use intensification is the potential deterioration of soil. The North Otago Rolling Downlands (NORD) region of New Zealand is drought prone, and although traditionally limited to extensive sheep farming, there are large-scale conversions to intensive cattle grazing operations such as dairy farming resulting from an irrigation scheme commissioned in 2006. Pallic soils (Aeric Fragiaqualf in US Soil Taxonomy) such as those in the NORD region are prone to soil compaction because of their ‘high’ structural vulnerability under intensive management. To address these concerns, a field trial was established on a common NORD Pallic soil (Timaru silt loam) to determine how land-use intensification affects indicators of soil quality (macroporosity, bulk density, structural condition score, total and mineralizable carbon and nitrogen and earthworms) and pasture production. The treatments compare irrigatedv. dryland pasture and sheepv. cattle grazing on 16 plots. The findings show that soil physical quality responds more quickly to changes in land-use pressure than do biochemical and organic indicators. Both irrigation and cattle grazing, particularly in combination, increased soil compaction; macroporosity on irrigated plots grazed by cattle ranged from 9·1 to 13·3% v/v at a depth of 0–50 mm, compared to dryland plots with sheep grazing (18·9–23·0% v/v). Soil compaction/damage has implications for pasture production, soil hydrology and nutrient movement. Land management practices for intensive cattle grazing of irrigated soil prone to treading damage therefore need to implement high compaction risk strategies to avoid or ameliorate potential changes to soil quality.

Growing maize in clumps as a strategy for marginal climatic conditions

Under dryland conditions of the Texas High Plains, maize ( Zea mays) production is limited by sparse and erratic precipitation that results in severe water stress particularly during grain formation. When plant populations are reduced to 2.0–3.0 plants m −2 to conserve soil water for use during grain filling, tillers often form during the vegetative growth and negate the expected economic benefit. We hypothesized that growing maize in clumps spaced 1.0 m apart would reduce tiller formation, increase mutual shading among the plants, and conserve soil water for grain filling that would result in higher grain yield. Studies were conducted during 2006 and 2007 at Bushland, TX. with two planting geometries (clump vs. equidistant), two irrigation methods (low-energy precision applicator, LEPA, and low-elevation spray applicator, LESA) at three irrigation levels (dryland, 75 mm and 125 mm in 2006; and dryland, 50 mm and 100 mm in 2007). For dryland plots in 2007, clump plants had only 0.17 tillers (0.66 tillers m −2) compared with 1.56 tillers per plant (6.08 tillers m −2) for equidistant spacing. Tillers accounted for 10% of the stover for the equidistant plants, but less than 3% of the grain. Clump planting produced significantly greater grain yields (321 g m −2 vs. 225 g m −2 and 454 g m −2 vs. 292 g m −2 during 2006 and 2007, respectively) and Harvest Indexes (0.54 vs. 0.49 and 0.52 vs. 0.39 during 2006 and 2007, respectively) compared with equidistant plants in dryland conditions. Water use efficiency (WUE) measurements in 2007 indicated that clumps had a lower evapotranspiration (ET) threshold for initiating grain production, but the production function slopes were 2.5 kg m −3 for equidistant treatments compared to 2.0 kg m −3 for clump treatments. There was no yield difference for method of irrigation on water use efficiency. Our results suggest that growing maize in clumps compared with equidistant spacing reduced the number of tillers, early vegetative growth, and Leaf Area Index (LAI) so that more soil water was available during the grain filling stage. This may be a useful strategy for growing maize with low plant populations in dryland areas where severe water stress is common.

Irrigation and soil physical quality: An investigation at a long‐term irrigation site

The hypothesis that irrigation improves soil quality by improving its moisture holding capacity compared to dryland (non‐irrigated) soils was tested using data on soil physical properties and irrigation frequency and timing (dryland, and irrigated at 10, 15, and 20% v/v and 3‐weekly) from a long‐term irrigation trial at Winchmore, South Island, New Zealand (soil type: Lismore silt loam). Despite previous work showing that macroporosity decreases and bulk density increases with irrigation and grazing, the most frequently irrigated plots showed no significant difference in these measurements, or in saturated and unsaturated hydraulic conductivity, compared to dryland plots. This implies that the soil had an inherent resilience to soil physical degradation. With time (years), the number of irrigations had declined and date of the first irrigation needed during the irrigation season had become later, leading to the perception of improved moisture holding capacity. This was supported by an increase in soil carbon concentrations in all treatments with time since development. Irrigations were scheduled, on average, at 10.9, 15.3 and 20.6% v/v for 10, 15, and 20% treatments, respectively, until 1997, but at 9.9, 14.1 and 19.2% for 10, 15, and 20% treatments, respectively, afterwards. However, several reasons explain this and refute the hypothesis of improved moisture holding capacity. The most pertinent was that irrigation timing was probably affected by the use of a gravimetric method prior to 1997, and a TDR‐based technique since. In addition, no difference was seen in pasture production relative to irrigation with time. Thus, apart from soil C concentrations there was little conclusive evidence to support the hypothesis that irrigation improves soil moisture holding capacity at this site.

Where to draw the line: Mapping of land rights in a South African commons

In South Africa, formal titles to land have generally been restricted to ‘commercial’ farms under white ownership. However, in Namaqualand in the Northern Cape Province, mapping of individual dryland plots became part of the land reform process. In this study, we take a critical look at this mapping exercise in the communal area of Concordia. While securing the rights of individual dryland plot holders, the mapping also resulted in unintended impacts. Separate plots were joined together, enclosing the communal corridors in between, and new individual plots were created, reducing the communal grazing area. Furthermore, the mapping and surveying process has triggered an upsurge in the fencing of dryland plots. The case demonstrates that formalisation may cause changes in rights in general, and may promote privatisation of communal rights more specifically. This experience from Namaqualand can be seen as a test case for possible effects of planned surveying and registration of individual plots in other South African communal areas.

Evaluation of Source Leaf Responses to Water-Deficit Stresses in Cotton Using a Novel Stress Bioassay

Water-deficit stresses preferentially reduce shoot growth, thereby disrupting the flow of carbohydrates from source leaves to the developing sinks. Here, we use a novel stress bioassay to dissect responses of field and greenhouse-grown cotton (Gossypium hirsutum) source leaves to water-deficit stresses. Fifth main stem leaf samples were harvested at sunrise and subjected to a prolonged elevated respiratory demand in the dark. Sucrose levels are lower in nonstressed cotton at sunrise compared to water-deficit stressed cotton, potentially predisposing the nonstressed tissue to succumb more rapidly. Tissue death was determined initially using the cell viability stain 2,3,5-triphenyltetrazolium chloride, but was determined in subsequent experiments by monitoring the decline in chlorophyll fluorescence yield. Fluorescence yield measurements were obtained within minutes of harvesting and individual samples were monitored over the time course of the treatment. Analyses of the time course and magnitude of chlorophyll fluorescence yield decline in samples from irrigated and dryland plots permitted the detection of stress responses within 24 h of the cessation of irrigation. The rate of fluorescence yield decline during the elevated respiratory demand treatment slowed as the water-deficit stress increased. Upon irrigation, the source leaves of the water-stressed plants recovered to prestress values within 4 d. Well-watered cotton overexpressing heat shock protein 101 had identical rates of fluorescence yield decline as nontransgenic cotton. These results suggest that the delayed decline in fluorescence yield of water-stressed tissue exposed to prolonged elevated respiratory demand can be used as a sensitive indicator of water-deficit stress responses.

Fall Rice Straw Management and Winter Flooding Treatment Effects on a Subsequent Soybean Crop

ABSTRACT The effects of fall rice (Oryza sativa L.) straw management and winter flooding on the yield and profitability of subsequent irrigated and dryland soybean [Glycine max (L.) Merr.] crops were studied for 3 years. Rice straw treatments consisted of disking, rolling, or standing stubble. Winter flooding treatments consisted of maintaining a minimum water depth of 10 cm by pumping water when necessary, impounding available rainfall, and draining fields to prevent flooding. The following soybean crop was managed as a conventional-tillage system or no-till system. Tillage system treatments were further divided into irrigated or dryland. Results indicated that there were no significant effects from either fall rice straw management or winter flooding treatments on soybean seed yields. Soybean seed yields for the conventional-tillage system were significantly greater than those for the no-till system for the first 2 yrs and not different in the third year. Irrigated soybean seed yields were significantly greater than those from dryland plots for all years. Net economic returns averaged over the 3 yrs were greatest ($390.00 ha−1) from the irrigated no-till system.

Fourwing Saltbush Seed Yield and Quality: Irrigation, Fertilization, and Ecotype Effects

Abstract Clones of superior pollen- and seed-producing plants of 4 fourwing saltbush ( Atriplex canescens [Pursh] Nutt.) ecotypes were planted in a seed orchard in west-central Texas to determine if seed production and quality could be enhanced by irrigation and fertilization. Subplots of nitrogen (N) at 112 kg·ha −1 , phosphorous (P) at 112 kg·ha −1 , N + P at 112 + 112 kg·ha −1 , or no fertilizer were superimposed on irrigated or dryland main-plots. Neither irrigation nor fertilization affected estimated seed yields or utricle fill during the third growing season after planting. Fertilization did not affect seed germination of any of the saltbush ecotypes on irrigated plots or that of the 2 more xeric ecotypes (Grandfalls and Valentine) on dryland plots. Fertilizer N on dryland plots increased germination of the San Angelo ecotype, and N + P increased germination of the Texon ecotype. Estimated gross value of the first seed crop was about $4 648·ha −1 even though the superior reproductive traits of parental pistillate plants were poorly expressed by the clones. Fertilization did not affect estimated seed yields in irrigated plots, but N and N + P increased seed yields in dryland plots in the fourth growing season. Fertilization effects on seed weights varied among irrigated and dryland plots and among saltbush ecotypes. Mortality of the shrubs during the period extending from 1988 to 1990 was not affected by irrigation or fertilization but increased among ecotypes as the xeric nature of their sites of origin increased and as the distance of their sites of origin from the seed orchard increased. Evidence from this study did not strongly support cloning, irrigation, or fertilization for improving seed harvests of fourwing saltbush in west-central Texas.

Fourwing Saltbush Seed Yield and Quality: Irrigation, Fertilization, and Ecotype Effects

Clones of superior pollen- and seed-producing plants of 4 fourwing saltbush (Atriplex canescens [Pursh] Nutt.) ecotypes were planted in a seed orchard in west-central Texas to determine if seed production and quality could be enhanced by irrigation and fertilization. Subplots of nitrogen (N) at 112 kg ha-1, phosphorous (P) at 112 kg ha-1, N + P at 112 + 112 kg ha-1, or no fertilizer were superimposed on irrigated or dryland main-plots. Neither irrigation nor fertilization affected estimated seed yields or utricle fill during the third growing season after planting. Fertilization did not affect seed germination of any of the saltbush ecotypes on irrigated plots or that of the 2 more xeric ecotypes (Grandfalls and Valentine) on dryland plots. Fertilizer N on dryland plots increased germination of the San Angelo ecotype, and N + P increased germination of the Texon ecotype. Estimated gross value of the first seed crop was about 4648~ha-1 even though the superior reproductive traits of parental pistillate plants were poorly expressed by the clones. Fertilization did not affect estimated seed yields in irrigated plots, but N and N + P increased seed yields in dryland plots in the fourth growing season. Fertilization effects on seed weights varied among irrigated and dryland plots and among saltbush ecotypes. Mortality of the shrubs during the period extending from 1988 to 1990 was not affected by irrigation or fertilization but increased among ecotypes as the xeric nature of their sites of origin increased and as the distance of their sites of origin from the seed orchard increased. Evidence from this study did not strongly support cloning, irrigation, or fertilization for improving seed harvests of fourwing saltbush in west-central Texas.

Water-use efficiency and the effect of water deficits on crop growth and yield of Kabuli chickpea (Cicer arietinum L.) in a cool-temperate subhumid climate

The present study was conducted from 1998 to 2000, to evaluate seasonal water use and soil-water extraction by Kabuli chickpea (Cicer arietinum L.). The response of three cultivars to eight irrigation treatments in 1998/99 and four irrigation treatments in 1999/2000 at different growth stages was studied on a Wakanui silt loam soil in Canterbury, New Zealand. Evapotranspiration was measured with a neutron moisture meter and water use efficiency (WUE) was examined at crop maturity. Water use was about 426 mm for the fully irrigated treatment and at least 175 mm for the non-irrigated plants. There was a significant correlation (P&lt;0·001) between water use and biomass yield (R2=0·80) and water use and seed yield (R2=0·75). There were also highly significant (P&lt;0·001) interacting effects of irrigation, sowing date and cultivar on WUE and the trend was similar to that for seed yield. The estimated WUE ranged from 22–29 kg DM/ha per mm and 10–13 kg seed yield/ha per mm water use.The three chickpea cultivars were capable of drawing water from depths greater than 60 cm. However, most of the water use (0·49–0·93 mm/10 cm soil layer per day) came from the top 0–30 cm, where most of the active roots were concentrated. The study has shown that using actual evapotranspiration and water-use efficiency, the biomass yield and seed yield of Kabuli chickpeas can be accurately predicted in Canterbury. Soil water shortage has been identified as a major constraint to increasing chickpea production. Drought was quantified using the concept of maximum potential soil moisture deficit (Dpmax) calculated from climate data. Drought responses of yield, phenology, radiation use efficiency and yield components were determined, and were highly correlated with Dpmax. The maximum potential soil moisture deficit increased from about 62 mm (irrigated throughout) to about 358 mm (dryland plots). Chickpea yield, intercepted radiation and the number of pods per plant decreased linearly as the Dpmax increased. Penman's irrigation model accurately described the response of yield to drought. The limiting deficit for this type of soil was c. 165 and 84 mm for the November and December sowings in 1998/99 and 170 mm in 1999/2000. Beyond these limiting deficits, yield declined linearly with maximum potential soil moisture deficits of up to 358 mm. There was little evidence to support the idea of a moisture sensitive period in these Kabuli chickpea cultivars. Yield was increased by irrigating at any stage of crop development, provided that the water was needed as determined by the potential soil moisture deficit and sowing early in the season.

Effects of summer irrigation and trampling in dairy pastures on soil physical properties and earthworm number and species composition

In 1989 a replicated split-plot trial on a Krasnozem soil was established at Elliott Research Station (ERS) in the north-west of Tasmania, as well as 14 on-farm trials in newly irrigated pastures on 3 different soil types (Alluvial, Podzolic, Krasnozem) in the dairy districts of Scottsdale, Smithton, and Deloraine. There were 3 main treatments at ERS: irrigated before grazing, irrigated after grazing, and grazed and not irrigated. Part of each main plot was fenced to prevent trampling but still allowed grazing. Effects of summer irrigation and trampling by dairy cows were examined for pasture production, and soil chemical and structural properties. Summer irrigation at ERS and on-farm trials has led to a decline in soil structure indicated by slower ponded water in filtration rates on irrigated plots compared with the dryland plots. The decline in ponded water in filtration rates suggests a reduction in macroporosity, especially in the soil surface. However, other indicators for soil structural change in the top 100 mm|percentage water-stable aggregates (&gt;2·5 mm) and bulk density|revealed no significant variation between the irrigated and dryland paddocks. There were, however, higher water in filtration rates and lower bulk densities in the untrampled areas than the trampled areas at ERS. Pasture production at ERS was about 50% more with irrigation in each of the 2 years of the study. Data collected at ERS in autumn and spring on the numbers of Aporrectodea caliginosa(Savigny) and Lumbricus rubellus (Hoffmeister) earthworms showed that they respond quite differently to irrigation. After 2 irrigation seasons, A. caliginosa numbers in irrigated plots dropped by over 50%, whereas in the dryland plots densities of this earthworm have remained around 390 earthworms/m 2. In contrast the densities of L. rubellus at ERS rose under irrigation practices, especially in the autumn{winter sampling period. Therefore, with the advent of summer irrigation at ERS, there was a shift in earthworm composition from a fauna dominated by A. caliginosa to a fauna with an increasing proportion of L. rubellus and a decreasing number of A. caliginosa. The typical dairy pasture in the on-farm trials recorded 2 main species, A. caliginosa (70%) and L. rubellus (30%). Total earthworm densities were highest in the north-west (Smithton) region of the State (293{351 earthworms/m 2) regardless of soil type, and the lowest densities were recorded in the Alluvial soils of Deloraine (96 earthworms/m 2). The north-west area also had the most diverse earthworm fauna, with 5 species recorded in one site: A. caliginosa, A. longa, Allolobophora chlorotica, L. rubellus, and O. cyaneum. Summer irrigation effects after 2 seasons on earthworm composition and abundance on dairy farms caused no significant change in A. caliginosa numbers, but there was a 45% increase in the numbers of L. rubellus in irrigated treatments. L. rubellus was considerably more active over summer in irrigated paddocks (25 earthworms/m 2) than in non-irrigated paddocks (7 earthworms/m 2). In contrast the number of A. caliginosa recorded in dryland paddocks was not statistically different to the irrigated paddocks, but the A. caliginosa in dryland paddocks were mostly inactive 8-20 mm from the soil surface.