Improving Irrigation Scheduling and Water use Efficiency in Cotton

Cotton (Gossypium hirsutum L) is an important crop in the southern United States. The crop is grown in both irrigated and rainfed situations and is seldom free from periods of water shortages at some stage during the season. In recent years the need for consistency in yields and a stable cash flow has resulted in a rapid expansion in the number of irrigated acres of cotton in the Mississippi Delta. Irrigation research has, however, not kept pace with this expansion. This project represents a start at meeting this urgent need. The influence of weather patterns necessitates that these studies be conducted over several years, and the results given here are, therefore, only preliminary observations. The early termination of irrigation has not resulted in any significant decrease in yield or lint quality on the Sharkey clay, although there was a slight detrimental trend when irrigation was terminated too early in August. These studies have helped to clarify the relationship between soil-moisture deficit and plant stress, especially as relates to yield, for cotton cropped on a Sharkey clay soil. Evaluation of crop indicators of water deficit showed that leaf water potential and the air-canopy temperature differential are reliable indicators of the onset of water stress. Leaf extension growth is also a sensitive indicator, but of no practical value in irrigation management. With further research, leaf water potential and canopy-air temperature differentials could provide useful indicators for use in conjunction with traditional methods of scheduling irrigation for cotton in the humid mid-south. A better understanding of the irrigation requirements of the crop will improve management and will have a very significant dollar reduction in the cost of production of the crop

Assessing the Reliability of Thermal and Optical Imaging Techniques for Detecting Crop Water Status under Different Nitrogen Levels

Efficient management of irrigation water is fundamental in agriculture to reduce the environmental impacts and to increase the sustainability of crop production. The availability of adequate tools and methodologies to easily identify the crop water status in operating conditions is therefore crucial. This work aimed to assess the reliability of indices derived from imaging techniques\u2014thermal indices (Ig (stomatal conductance index) and CWSI (CropWater Stress Index)) and optical indices (NDVI (Normalized Difference Vegetation Index) and PRI (Photochemical Reflectance Index))\u2014as operational tools to detect the crop water status, regardless the eventual presence of nitrogen stress. In particular, two separate experiments were carried out in a greenhouse, on two spinach varieties (Verdi F1 and SV2157VB), with different microclimatic conditions and under different levels of water and nitrogen application. Statistical analysis based on ANOVA test was carried out to assess the independence of thermal and optical indices from the crop nitrogen status. These imaging indices were successively compared through correlation analysis with reference destructive and non-destructive measurements of crop water status (stomatal conductance, chlorophyll a fluorescence, and leaf and soil water content), and linear regression models of thermal and optical indices versus reference measurements were calibrated. All models were significant (Fisher p-value lower than 0.05), and the highest R2 values (greater than 0.6) were found for the regression models between CWSI and the soil water content, NDVI and the leaf water content, and PRI and the stomatal conductance. Further analysis showed that imaging indices acquired by thermal cameras (especially CWSI) can be used as operational tools to detect the crop water status, since no dependence on plant nitrogen conditions was observed, even when the soil water depletion was very limited. Our results confirmed that imaging indices such as CWSI, NDVI and PRI can be used as operational tools to predict soil water status and to detect drought stress under different soil nitrogen conditions

Canopy Resistance as Affected by Soil and Meteorological Factors in Potato

Precision irrigation requires a method of quantifying the crop water status or root zone depletion of water to determine when and how much water to apply to the soil. Changes in canopy resistance (rc) and canopy temperatures have the potential of being used as a crop water status indicator for irrigation management. A study was conducted on potato (Solanum tuberosum L.) grown in northern Egypt at Shibin El-Kom on an alluvial loamy soil for winter (20 Sept. 2001 through 20 Jan. 2002) and spring (1 Feb. 2002 through 20 May 2002) seasons to determine if rc derived from energy balance and plant parameters could be used to determine the onset of water stress and the amount of water required to refill the soil profile. Diurnal rc was determined for well-watered conditions and achieved minimum values of 20 and 10 s m-1 at noontime during winter and spring periods, environmenrespectively. A power relationship of -0.86 for well-watered conditions was developed between rc and net radiation (Rn) at various plant growth stages. In deficit soil water conditions, rc increased linearly with decreasing available soil water (ASW), with a change in potato rc of 0.75 and 0.39 s m-1 per percentage ASW for 1 and 2 MJ m-2 h-1 of Rn at midgrowth, respectively. A ratio of actual/potential canopy resistance (rc/rcp) was derived to normalize the meteorological differences between growing seasons. This ratio was 2.5 when 50% of ASW was removed and can be used as a parameter to determine the need for irrigations using weather factors and canopy temperature. Canopy resistance increased linearly with increasing soil solution salinity, electrical conductivity, when the soil solution was above the threshold soil salinity value. A ratio of rc/rcp was found to normalize the effects of different environments across saline and water deficit conditions

Canopy Resistance as Affected by Soil and Meteorological Factors in Potato

Precision irrigation requires a method of quantifying the crop water status or root zone depletion of water to determine when and how much water to apply to the soil. Changes in canopy resistance (rc) and canopy temperatures have the potential of being used as a crop water status indicator for irrigation management. A study was conducted on potato (Solanum tuberosum L.) grown in northern Egypt at Shibin El-Kom on an alluvial loamy soil for winter (20 Sept. 2001 through 20 Jan. 2002) and spring (1 Feb. 2002 through 20 May 2002) seasons to determine if rc derived from energy balance and plant parameters could be used to determine the onset of water stress and the amount of water required to refill the soil profile. Diurnal rc was determined for well-watered conditions and achieved minimum values of 20 and 10 s m-1 at noontime during winter and spring periods, environmenrespectively. A power relationship of -0.86 for well-watered conditions was developed between rc and net radiation (Rn) at various plant growth stages. In deficit soil water conditions, rc increased linearly with decreasing available soil water (ASW), with a change in potato rc of 0.75 and 0.39 s m-1 per percentage ASW for 1 and 2 MJ m-2 h-1 of Rn at midgrowth, respectively. A ratio of actual/potential canopy resistance (rc/rcp) was derived to normalize the meteorological differences between growing seasons. This ratio was 2.5 when 50% of ASW was removed and can be used as a parameter to determine the need for irrigations using weather factors and canopy temperature. Canopy resistance increased linearly with increasing soil solution salinity, electrical conductivity, when the soil solution was above the threshold soil salinity value. A ratio of rc/rcp was found to normalize the effects of different environments across saline and water deficit conditions

Disentangling the effect of farming practice and aridity on crop stable isotope values: a present-day model from Morocco and its application to early farming sites in the eastern Mediterranean

Agriculture has played a pivotal role in shaping landscapes, soils and vegetation. Developing a better understanding of early farming practices can contribute to wider questions regarding the long-term impact of farming and its nature in comparison with present-day traditional agrosystems. In this study we determine stable carbon and nitrogen isotope values of barley grains from a series of present-day traditionally managed farming plots in Morocco, capturing a range of annual rainfall and farming practices. This allows a framework to be developed to refine current isotopic approaches used to infer manuring intensity and crop water status in (semi-)arid regions. This method has been applied to charred crop remains from two early farming sites in the eastern Mediterranean: Abu Hureyra and ‘Ain Ghazal. In this way, our study enhances knowledge of agricultural practice in the past, adding to understanding of how people have shaped and adapted to their environment over thousands of years

Monitoring of emerging water stress situations by thermal and vegetation indices in different almond cultivars

In recent years, the area dedicated to modern irrigated almond plantations has increased significantly in Spain. However, the legal irrigation allocations are lower than the maximum water requirements of the crop in most cases. Therefore, almond growers are forced to implement regulated deficit irrigation strategies on their farms, applying water stress in certain resistant phenological periods and avoiding it in sensitive periods. Given the need to monitor the water status of the crop, especially in the most sensitive periods to water stress, the objective of this work was to evaluate the sensitivity of two UAV-based crop water status indicators to detect early water stress conditions in four almond cultivars. The field trial was conducted during 2020 in an experimental almond orchard, where two irrigation strategies were established: full irrigation (FI), which received 100% of irrigation requirements (IR), and regulated deficit irrigation (RDI), which received 70% of IR during the whole irrigation period except during the kernel-filling stage when received 40% IR. The UAV flights were performed on four selected dates of the irrigation season. The Crop Water Status Index (CWSI) and the Normalized Difference Vegetation Index (NDVI) were derived from thermal and multispectral images, respectively, and compared to classical water status indicators, i.e., stem water potential (Ψstem ), stomatal conductance (gs ), and photosynthetic rate (AN ). Of the four flights performed, three corresponded to mild water stress conditions and a single flight was performed under moderate water stress conditions. Under mild water stress, CWSI was not able to capture the differences between FI and RDI trees that were observed with Ψstem . Under moderate stress conditions, CWSI was sensitive to the water deficit reached in the trees and showed significant differences among both irrigation treatments. No differences were observed in the CWSI and NVDI response to water stress among cultivars. Although NDVI and CWSI were sensitive to water stress, the low signal intensity observed in NDVI makes this index less robust than CWSI to monitor crop water stress. It can be concluded that UAV-based CWSI measurements are reliable to monitor almond water status, although for early (mild) levels of water stress, Ψstem seems to be the preferred option.Junta de Andalucía AVA.AVA2019.05