Neil C. Hansen

Infrared Thermometry to Estimate Crop Water Stress Index and Water Use of Irrigated Maize in Northeastern Colorado

With an increasing demand of fresh water resources in arid/semi-arid parts of the world, researchers and practitioners are relying more than ever on remote sensing techniques for monitoring and evaluating crop water status and for estimating crop water use or crop actual evapotranspiration (ETa). In this present study, infrared thermometry was used in conjunction with a few weather parameters to develop non-water-stressed and non-transpiring baselines for irrigated maize in a semi-arid region of Colorado in the western USA. A remote sensing-based Crop Water Stress Index (CWSI) was then estimated for four hourly periods each day during 5 August to 2 September 2011 (29 days). The estimated CWSI was smallest during the 10:00-11:00 a.m. and largest during the 12:00-13:00 p.m. hours. Plotting volumetric water content of the topsoil vs. CWSI revealed that there is a high correlation between the two parameters during the analyzed period. CWSI values were also used to estimate maize actual transpiration (Ta). Ta estimates were more influenced by crop biomass rather than irrigation depths alone, mainly due to the fact that the effects of deficit irrigation were largely masked by the significant precipitation during the growing season. During the study period, applying an independent remotely sensed energy balance model showed that maize ETa was 159 mm, 30% larger than CWSI-Ta (122 mm) and 9% smaller than standard-condition maize ET (174 mm).

Phytosiderophore release as a criterion for genotypic evaluation of iron efficiency in oat

Abstract Iron (Fe) deficiency in small grains grown on calcareous soils results in reduced yields, is difficult and expensive to treat with fertilizer, and is complicated to overcome by genetic field screening due to heterogeneous soil and environmental conditions. Recently, phytosiderophore release has been linked to ability of species and genotypes to resist Fe‐deficiency chlorosis. We propose a laboratory technique to measure phytosiderophore release by Fe‐deficient oat (Avena sativa L.) genotypes as a selection method for Fe‐deficiency chlorosis resistance in oat. Plants were grown in Fe‐limiting nutrient solution and phytosiderophore release was measured on 11 days. Summations of daily phytosiderophore release by 17 oat genotypes correlate well with Fe‐deficiency chlorosis scores in the field (r = ‐0.70, p = 0.01). The proposed method consistently identified the genotypes most susceptible to Fe deficiency but did not clearly separate the moderately susceptible genotypes. In these latter genotypes, ot...

Winter cereal root growth and aboveground–belowground biomass ratios as affected by site and tillage system in dryland Mediterranean conditions

Background and aimsUnderstanding the interaction between crop roots and management and environmental factors can improve crop management and agricultural carbon sequestration. The objectives of this study were to determine the response of winter cereal root growth and aboveground–belowground biomass ratios to tillage and environmental factors in the Mediterranean region and to test an alternative approach to determine root surface area.MethodsWinter cereal root growth and biomass ratios were studied in three sites with different yield potential according to their water deficit (high yield potential, HYP; medium yield potential, MYP; low yield potential, LYP) in the Ebro Valley (NE Spain). At all sites, three tillage systems were compared (conventional tillage, minimum tillage, no-tillage (NT)). Root surface density (RSD), soil water content, yield components, and grain yield were quantified and shoot-to-root and grain-to-root ratios were calculated. RSD was measured with the use of image analysis software comparing its performance to a more common intersection method.ResultsSignificant differences on RSD between sites with different yield potential were found being the greatest at the HYP site and the lowest at the LYP one. Shoot-to-root ratio was 2.7 and 4.6 times greater at the HYP site than at the MYP and LYP sites, respectively. Moreover, the grain-to-root ratio was significantly affected by site, with a ratio that increased with yield potential. Tillage had no significant effects on RSD at any of the sites studied; however, tillage did affect grain yield, with NT having the greatest yields.ConclusionsThis study shows that in the Mediterranean dryland agroecosystems, winter cereals relative above- and belowground biomass growth is strongly affected by the yield potential of each area. NT in the Mediterranean areas does not limit cereal root growth and leads to greater grain yields. A highly significant linear relationship (P < 0.001; r2 0.77) was observed between the root surface values obtained with the free-software image analysis method and the most common intersection method, showing it to be a reliable method for quantifying root density.

Modified procedures for commercial adaptation of root iron-reducing capacity as a screening technique

Abstract Genotypic evaluation is critical to development of soybean [Glycine max (L.) Merr.] cultivars with genetic resistance to Fe‐deficiency chlorosis. Root Fe3+ reducing activity is correlated with genotypic resistance to Fe chlorosis measured in field nurseries, and thus may be a reliable method for identifying chlorosis‐resistat genotypes. However, to develop methods useful for large‐scale screening, several modifications of the previously published procedure for measuring root Fe3+ reducing activity were investigated. Several hydroponic experiments were conducted to test proposed modifications. It was determined that: (a) different genotypes may be grown together in the same nutrient solution without affecting Fe3+ reduction, (b) genotype separation is maximized by growth in CaCO3 buffered solution (37.5 mg L−1), (c) a labor‐intensive elongation step can be eliminated, and (d) denotype evaluation can be accomplished without introducing Fe into the hydroponic solutions. These refinements to the proc...

Conserving and Optimizing Limited Water for Crop Production

Proper soil and crop management systems are critical for sustainable production in semi-arid environments, and there are principles that apply to both dryland (non-irrigated) and limited-irrigation systems. In the non-irrigated environment, crop residue from no-till systems permits more diverse crop rotations with less frequent fallow, which leads to increased precipitation-use efficiency. Soil improvements from no-till systems include decreased soil erosion, increased soil organic matter, improved soil structure, and increased infiltration rate. These soil improvements create a positive feedback loop by making more water available to the crop, increasing yields, and returning more crop residues to the soil. In the Great Plains of the United States, we have found that annualized grain production from no-till systems with less frequent fallow can be increased by 75% with an increase in economic return from 13% to 36% compared with the traditional wheat-fallow cropping system. There is also a need to increase water productivity for irrigated crop production because of competition for water by municipal and industrial users, drought, and declining groundwater supplies. The adoption of cropping systems that use less water and insure economic sustainability must be developed. We have found that limited-irrigation practices that time irrigations with critical growth stages can reduce water use of corn by 50% while reducing yields by only 30%. Alfalfa was found to have great potential for limited irrigation because of its natural drought tolerance and perennial growth habit. Many of the principles of water-conservation practices identified in the United States are adaptable to Indias conditions. Soil and crop management systems that use less water and that are sustainable and economically viable in Indias limited water environment must be developed.

Diurnal rhythmicity of root iron reduction in soybean as affected by various light regimes

Abstract Root iron (Fe) reduction is correlated with genotypic Fe efficiency in soybean (Glycine max L. Merr.) and is reportedly a reliable method for identifying chlorosis‐resistant genotypes. If used on a large‐scale, it would be advantageous to measure Fe reduction at various times of the day. Experiments were conducted to determine whether such a practice is possible without affecting the accuracy of the results. Despite extensive understanding of Fe‐reducing activity in dicots, it is not known if root Fe reduction shows diurnal rhythmicity similar to phytosiderophore release, the Fe‐deficiency stress response of grasses.. Five soybean cultivars showed a diumally rhythmic pattern of root Fe reduction when grown in a normal 16‐h light, 8‐h dark cycle. Continuous illumination (no dark) slowed Fe reduction and eliminated the rhythmic pattern as well as any correlation between root Fe reduction and Fe efficiency. Preceding a continuous light period with two 16‐h light, 8‐h dark cycles did not improve the ...

Behavior of atrazine in limited irrigation cropping systems in Colorado: prior use is important.

Glyphosate-resistant (GR) corn may be a major component of new cropping systems to optimize the use of limited irrigation water supply while sustaining production. Because atrazine is an important tool for residual weed control in GR corn, we examined atrazine binding to soil, dissipation, movement, and early season weed control in limited and full irrigation cropping systems. These systems included continuous corn under conventional tillage and full irrigation (CCC-FI) and under no-tillage and deficit irrigation (CCC-DI), a sunflower-wheat-corn rotation under no-tillage and deficit irrigation (SWC-DI), and a wheat-fallow-wheat-corn rotation under no tillage and natural precipitation (WFWC-NP). Crop rotation and herbicide use history influenced atrazine behavior more than amount or type of irrigation. Atrazine dissipated more rapidly in the top 30 cm of soil in the CCC-FI and CCC-DI plots (half-life [T(1/2)] = 3-12 d), which had received previous applications of the herbicide, compared with the SWC-DI and WFWC-NP plots, which had no history of atrazine use (T(1/2) = 15-22 d). Laboratory assays indicated that the different rates of degradation were at least partly due to differences in microbial degradation in the soil. Atrazine moved the most in the top 30 cm in the SWC-DI and WFWC-NP plots. This greater movement is probably due to the slower rate of atrazine degradation. Studies of the behavior of pre-emergence herbicides in new limited irrigation cropping systems must consider all characteristics of the systems, not just amount and timing of irrigation.

Conservation Agriculture in North America

Conservation agriculture (CA) is a production paradigm that groups reduced tillage, mulching with crop residues or cover crops, and diversified crop rotations, especially those that incorporate leguminous crops. In North America, reduced tillage is the most widely adopted practice that seeks the ideals of CA and adoption rates are increasing. Cover crops are used on a low percentage of cultivated land in North America, but recent efforts to promote the value of cover cropping have resulted in increased adoption rates. Developing cropping systems that use biomass for biofuel systems has potential for expanding the cultivation of cover crops. This chapter illustrates the diversity in CA adoption in North America by describing CA adoption in contrasting production regions with variations in climate, soil types, and cropping systems. Zero-till adoption has been more popular in regions where growing seasons are not limited by cold conditions and with moderate levels of crop residue. Zero-till adoption has been limited by difficulties in seeding and the development of weed resistance to common herbicides. Strip tillage has evolved as an alternative conservation tillage practice and is being adopted widely across North America. Future CA systems will allow for conservation practices, such as tillage intensity, to be applied in a spatially variable way that matches conservation costs and benefits with specific conditions in fields and watersheds.

Investigating Anthropogenic and Geogenic Sources of Groundwater Contamination in a Semi-Arid Alluvial Basin, Goshen Valley, UT, USA

Groundwater resources can be impacted by contamination from geogenic and anthropogenic inputs but it can be difficult to disentangle contaminant sources. In this study, we investigated the sources and distribution of NO3 and As in Goshen Valley, UT, a semi-arid alluvial basin in the western USA that contains geothermal waters, playa soils, agriculture, and legacy mining. Surface water, springs, and wells were analyzed for As and NO3 concentrations in relation to major ions, trace elements, and stable isotopes in water (δ18O and δD), and other isotopic tracers. Major ion concentrations showed high spatial variability ranging from freshwater to brackish water, with the highest salinity found in geothermal springs and springs discharging from playa sediments (Playa Springs). Radiogenic 87Sr/86Sr ratios in the Playa Springs suggest that Sr is sourced from crystalline basement rocks. The highest NO3 concentrations were found in groundwater beneath agricultural areas, particularly dairy farms, with isotopic values indicating manure, not fertilizers, as the major source. Many of the NO3-contaminated wells contained old groundwater (based on 14C and 3H), suggesting that reinfiltration of pumped groundwater may be a source of NO3 pollution. The Playa Springs also had the highest As concentrations, with moderate As concentrations found in other geothermal springs. Wells containing moderate As concentrations were found in areas where the groundwater interacts with alluvial sediments or carbonate rocks. Surprisingly, nearby mining and mineral processing seems to have minimal effect on As contamination in the alluvial aquifer. This study has implications for understanding water quality in regions that are impacted by multiple potential contaminant sources.

Leaf temperature of maize and Crop Water Stress Index with variable irrigation and nitrogen supply

Crop canopy temperature and Crop Water Stress Index (CWSI) are used for assessing plant water status and irrigation scheduling, but understanding management interactions is necessary. This study evaluated whether nutrient deficiencies would confound interpretation of plant water status from leaf temperature. Leaf temperature and CWSI in maize (Zea mays L.) were evaluated with different irrigation strategies and varying nitrogen (N) supply for replicated glasshouse and field studies. Glasshouse treatments consisted of well-watered or simulated drought and sufficient, intermediate, or deficient N. Field study treatments consisted of well-watered, controlled deficit irrigation, or simulated drought and sufficient, sufficient delayed, or deficient N. Average CWSI values varied across irrigation treatments, with 0.37 and 0.54 for glasshouse well-watered and drought and 0.34, 0.47, and 0.51 for field well-watered, drought, and controlled deficit treatments, respectively. Nitrogen levels created widely different leaf chlorophyll contents without affecting leaf temperature or CWSI. Canopy water stress measurements were robust across varying N levels, but CWSI did not correlate well with leaf area due to confounding effects of irrigation timing and nitrogen levels. Leaf temperature and CWSI are useful for evaluating crop water status, but nutrient status and timing of water stress must also be considered for crop growth prediction.