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Nodal and primary roots have distinct responses to soil moisture that depend on species. They can be selected independently in a breeding programme to shape root architecture. A rapid rate of plant development and enhanced responsiveness to local moisture may be traits that favour nodal roots and water use efficiency at no cost to shoot growth.

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Drought, and rising water and pumping costs dictate that continued production of corn (Zea mays L.) will be limited in future years if effective water conservation strategies are not established. This study was conducted to evaluate the effect of irrigation regimes in conjunction with surfactant treatments on field corn grain yield (GY), total dry matter (TDM) production, and irrigation water use efficiencies (IWUE) based on GY and TDM in a distinct Mediterranean climate, at Spadra Ranch in Pomona, CA, for 2 yr (2008 and 2009). The field experiment was set up in a split plot design with four replications where irrigation regimes (I40: 40%, I60: 60%, I80: 80%, and I100: 100% of the estimated evapotranspiration) was the main plot and application of surfactant (water treated with surfactant and no surfactant application) was assigned to the subplot. The results showed a stepwise reduction in TDM and GY in treatments both with and without surfactant as water deficit increased. However, surfactant application at any irrigation level resulted in higher GY and TDM compared to no‐surfactant treatments. Irrigation water use efficiency based on TDM and GY was the highest in I40 and the lowest in full irrigation (I100) conditions. By application of surfactant in irrigation water, both IWUE and GY increased. Surfactant application increased irrigation costs by 4.7%; however, it increased profit by 19.75%. Economic evaluation showed that the grain yield increment could compensate surfactant price and consequently the same profit achieved with applying 40% less water plus surfactant compared with 100% crop evapotranspiration with no surfactant application. In a Mediterranean climate and under limited irrigation conditions, corn could be cultivated with acceptable yields by application of surfactant.

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Non-ionic surfactants have been well researched as a tool to ameliorate water repellent conditions. However, few studies have evaluated the risks and benefits of non-ionic surfactant applications in wettable soil. The objective of this study was to evaluate the effects of a surfactant in modifying the wetting pattern in soils of different textures and organic matter contents. The experimental treatments consisted of (1) four different soil textures including sandy, sandy loam, sandy clay loam and silt loam, (2) four different organic matter contents (0.2, 0.7, 1.2 and 1.7% by weight), and (3) irrigation water treatments with or without surfactant (IrrigAid Gold). The experiment was carried out in Plexiglas boxes with one drip emitter under the soil surface. The results demonstrated the superiority of surfactant application on increasing water distribution in the soil profile for all soil textural classes. Silt loam texture had the highest side wetted area and wetting depth 45min after the initiation of irrigation. Upward capillary water movement and top wetted area significantly decreased in the surfactant treatment across all soil textures except in sandy soil. As organic matter content increased, top wetted area decreased. These findings clarified the potential ability of surfactant in increasing water infiltration in non-repellent soil in an in vitro system.

Plant photosynthesis is a major part of the global carbon cycle and climate system. Carbon capture by C3 plants is most often modelled using the Farquhar-von-Caemmerer-Berry (FvCB) equations. We undertook a global synthesis of all parameters required to solve the FvCB model. The publicly available dataset we assembled includes 3663 observations from 359 different plant species among 96 taxonomic families coming from every major vascular plant clade (lycophytes, ferns, gymnosperms, magnoliids, eudicots and monocots). Geographically, the species in the database have distributions that span the majority of the globe. We used the model to predict photosynthetic rates for the average plant in each major terrestrial plant clade and find that generally plants have dramatically increased their photosynthetic abilities through evolutionary time, with the average monocot (the youngest clade) achieving maximum rates of photosynthesis almost double that of the average lycophyte (the oldest clade). However, there was no evidence of niche conservatism with most variance occurring within, rather than among clades (K=0.357, p=0.001). We also solved the model for different average plant functional types (PFTs) and find that herbaceous species generally have much higher rates of photosynthesis compared to woody plants. Indeed, the maximum photosynthetic rate of graminoids is almost three times the rate of the average tree. The resulting functional responses to increasing CO2 suggest that most groups are already at or near their maximum rate of photosynthesis. Unfortunately, only graminoids seem to have the capacity to continue to increase photosynthetic rates with increasing CO2 concentrations in the atmosphere. We view this as version 1.0 of a database for global photosynthesis parameters and functional responses and hope that the publicly available dataset can improve models of photosynthesis.