Soybean Growth, Development and Productivity in Response to Flood Stress at Reproductive Stage

Objectives The objectives of this study were to investigate the impact of flooding on: Reproductive, growth, and development Nutrient concentration Soybean productivity and resilient in changing environment Methods An out-door pot-culture experiment was conducted to determine flooding effects on soybean growth and physiology during the reproductive period. Cultivar Asgrow AG5332 was seeded in 5.2 L pots filled with 3:1 by volume fine sand and topsoil and irrigated with full-strength Hoagland's nutrient solution. After 34 days of sowing, treatments were induced flooding at 2.5 cm above the soil surface for 16 additional days. Measurements were made on soil oxygen content and leaf gas exchange and pigment. Growth parameters and plant components biomass were also measured, 66 days after sowing. Results Soil oxygen levels declined rapidly to 0% in around 5-days of flood treatment, but the control remained 18%. The nutrient: N and Mg concentrations significantly decreased with flooding. All plant growth parameters and reproductive potential declined in the treatments at P = 0.001. Pod numbers and weights as a measure of reproductive potential declined in the plants under flood conditions. Conclusions This study confirmed that the soybean plant during the reproductive period is highly sensitive to flooding. Flood-resistant cultivar should be encouraged by farmers to improve crop productivity and food security. Funding Sources United State Soybean Production Board USAID.

Oxygation to Unlock Yield Potential of Crops: A Review

Irrigated agriculture has played a vital role in supporting a dramatic increase in global food production over recent decades. However, only 20 per cent of the world’s agricultural land is irrigated. It produces 40 per cent of world’s food supply. Even the traditional practices of irrigation, in whatever form, will have transient of long term depressive effects of soil oxygen content. The depressive effect of irrigation on soil oxygen is higher for a given soil water potential on heavy clay soils (e.g., for vertisols) than on lighter soils Hence plants suffered from sub-optimal oxygen supply in the root zone and causes hypoxia and anoxia. Aeration of subsurface drip irrigation (SDI) has been shown to alleviate soil hypoxia/anoxia by providing air/oxygen to an oxygen-depleted plant root zone. This can be achieved by coupling an air injector venturi to draw air into the subsurface drip irrigation system is known as oxygation/aerogation/air injection. Oxygation assures optimal root function, microbial activity and mineral transformations, which lead to enhanced yield and water use efficiency under hypoxic (anaerobic) conditions. It also improves plant performance and yield under irrigated conditions (i.e. crops such as radish by 9.87 per cent and cotton lint yields by 10 per cent) previously considered to be satisfactory for crop growth and offers scope to offset some of the negative impacts of compaction and salinity related to poor soil aeration on crop growth. The aeration condition of irrigated soils deserves more attention than it has received in the past, if we wish to unlock yield potential constraints by soil oxygen limitations in irrigated areas and enhance the yield potential to meet the future food (and fibre) demand.

Analysis of soil oxygen dynamics as a diagnostic tool of the soil oxygen status in-situ

<p>Soil oxygen has been recognized as a potential limiting factor in plant production second only to water and nutrients. While it is widely accepted that soil gaseous oxygen levels below 10% V/V are detrimental to plant production, there are currently no accepted indices to quantify the effect of different agricultural practices on soil oxygen supply and availability. To address this challenge, a new approach is introduced, whereby indices describing the soil oxygen dynamics are determined using data from continuous in-situ soil oxygen measurements. To give the measurements a mechanistic interpretation, we developed a conceptual model describing the soil oxygen dynamics as a simplified mass balance between oxygen supply rate and oxygen consumption rate. The approach was applied to analyze field measurements of soil oxygen and water tension at 35 cm depth in avocado orchards irrigated with either Fresh Water (FW) or Treated Wastewater (TWW) in clay soil (~60% clay). The reliability of the method was shown, as soil respiration rates equivalent to 1-2 g O<sub>2</sub><sub></sub>m<sup>-2</sup> d<sup>-1</sup> were established, in line with previous reports for evergreen trees. The model defines the soil water tension at which oxygen supply to the measurement depth after irrigation surpasses the oxygen consumption rate as the critical soil water tension, and a value of ~50 mbar was established for the experiment site, again within the range described in the literature for soils with similar properties using other methodologies. Using the new approach, it was established that more hypoxic conditions occur in TWW irrigated plots as compared to FW irrigated plots due to a difference in the time required to reach the critical soil water tension – TWW irrigated plots took nearly 50% longer to reach a soil water tension of 50 mbar after each irrigation in the height of the irrigation season. This delay in TWW irrigated plots was directly related to the soil drying rate, which was lower in the TWW irrigated soils in both night and day periods, indicating both a hindering of drainage and of plant water uptake. In a second study site, the values describing the soil oxygen dynamics were found to relate to the soil stone content (particles>2mm), a known effector of soil aeration. By utilizing in-situ<sub></sub>measurements, the method aims to represent the intricate interrelations occurring in the field which may be missed using methods focusing on the individual factors affecting soil oxygen. The insights gained can provide the basis for designing management techniques to resolve unfavorable low oxygen levels in agriculture, as well as in natural environments where hypoxia affects soil carbon turnover, the evolution of greenhouse-gasses, and the fate of toxic elements in soils.</p>

Exploring the oxygen sensitivity of wetland soil carbon mineralization

Soil oxygen availability may influence blue carbon, which is carbon stored in coastal wetlands, by controlling the decomposition of soil organic matter. We are beginning to quantify soil oxygen availability in wetlands, but we lack a precise understanding of how oxygen controls soil carbon dynamics. In this paper, we synthesize existing data from oxic and anoxic wetland soil incubations to determine how oxygen controls carbon mineralization. We define the oxygen sensitivity of carbon mineralization as the ratio of carbon mineralization rate in oxic soil to this rate in anoxic soil, such that higher values of this ratio indicate greater sensitivity of carbon mineralization to oxygen. The estimates of oxygen sensitivity we derived from existing literature show a wide range of ratios, from 0.8 to 33, across wetlands. We then report oxygen sensitivities from an experimental mesocosm we developed to manipulate soil oxygen status in realistic soils. The variation in oxygen sensitivity we uncover from this systematic review and experiment indicates that Earth system models may misrepresent the oxygen sensitivity of carbon mineralization, and how it varies with context, in wetland soils. We suggest that altered soil oxygen availability could be an important driver of future blue carbon storage in coastal wetlands.