Temperature and soil moisture impact micronutrient uptake

Wheat, pea and canola uptake of copper (Cu), zinc (Zn) and boron (B) was greater with optimum soil moisture and warm temperatures compared to drought and saturated soil moisture conditions or cold temperatures.

Micronutrient deficiencies can occasionally occur on Prairie soils, but crop response to fertilization can be unpredictable. The objectives of this study were to assess the impact of micronutrient fertilization of Cu, Zn and B on mobility, bioavailability, and growth responses of wheat, pea, and canola under varying temperature and soil moisture conditions.

Soil was collected from a field in the Brown soil zone near Central Butte, Saskatchewan, and a field in the Dark Brown soil zone near Alameda in south eastern Saskatchewan. In the growth chamber study, wheat and pea were grown in the Brown soil and canola was grown in the Dark Brown soil, reflecting typical rotations grown on the two fields.

The growth pots were fertilized with recommended rates of nitrogen (N), phosphorus (P), sulfur (S), and potassium (K) fertilizer prior to seeding. Sulfate fertilizer forms of Cu and Zn were applied at a rate of 4.45 lbs/ac (5 kg/ha), and B fertilizer was applied at 0.89 lbs/ac (1 kg/ha) using boric acid. All fertilizers were applied in a layer 2 cm below the soil surface to simulate a sub-surface band application.

The treatments included 2 temperature and 3 soil moisture environments implemented at early growth stages. The treatments simulated cool-wet or warm-dry extremes that can be encountered after seeding.

Initially, all three moisture treatments had the soil water content of each pot at field capacity (FC) and seeds were placed into moist soil. One week after seed germination, two moisture treatments were initiated while the third remained at field capacity. The other two treatments were drought stress (DS: 50% of field capacity), and saturated (S) conditions with soil submerged and all pores filled with water. These soil moisture conditions were maintained over the duration of the 6 week growing period.

After seeding, two temperature treatments were compared with cold (5C) and warm (23C daytime and 18C nighttime) temperatures for the first two weeks followed by warm temperatures for the remaining four weeks.

Impact on micronutrient availability varied

The supply rates of available Cu, Zn and B, as measured with Plant Root Simulator (PRS) probes, varied depending on nutrient and environmental stress. Available Cu and Zn supply was significantly lower under drought stressed conditions, attributed to greatly reduced ability of these micronutrients to move through the soil by diffusion under dry conditions.  Lowest soil supplies of available Cu and Zn were found under drought stress and cold temperature treatment combinations.

Drought stress or waterlogging and cold temperature combinations resulted in reduced plant uptake of all micronutrients.  The greatest uptake of Cu, Zn, and B by all three crops occurred with soil moisture at field capacity.  Uptake of Cu and Zn by pea and canola were significantly reduced by cold temperature.

Uptake of B by wheat, pea and canola was lower at field capacity when temperatures were cold, with wheat and pea uptake being lower than canola.

The lowest uptake of Zn by canola was observed with saturated soil conditions, and was further reduced under cold temperature.

Post-harvest, the extractable levels of Cu, Zn, and B  in the soil were mainly depleted by plant uptake or because of redox reactions under unfavorable moisture conditions.

Plant biomass yield impacted by environment

The highest biomass yield measured after 6 weeks of growth occurred with warm temperatures and field capacity soil moisture conditions for all crops. Field pea was most severely impacted by unfavourable moisture conditions of either drought or saturated soils with an average 95% reduction compared to field capacity soil moisture conditions.

Drought impacted wheat biomass yield more than saturated soil conditions. The opposite occurred in canola where the lowest biomass occurred with waterlogging and cold conditions. The combined effects of cold temperature and unfavorable soil moisture conditions were highly impactful on pea and canola development.

Biomass yield of wheat, pea, and canola grown under three different moisture and two temperature regimes

DS = Drought stress (50% of field capacity), FC = Field Capacity, and S = Saturated. Warm = 23C day and 18C night, and Cold = 5C

Source: Rahman et al. 2020

Overall, the growth chamber trial shows that cold temperatures and soil moisture stress can result in poor Cu, Zn, and B uptake by wheat, pea and canola. The researchers suggest that micronutrient fertilization practices may require application closer to roots or alternative applications such as foliar spray in order to overcome the effect of dry soil limiting the ability of micronutrient metals to move to root surfaces.

Financial support was provided by the Western Grains Research Foundation and Agriculture and Agri-Food Canada Agri-Innovation program.

Md. Noabur Rahman, Ryan Hangs & Jeff Schoenau (2020) Influence of soil temperature and moisture on micronutrient supply, plant uptake, and biomass yield of wheat, pea, and canola, Journal of Plant Nutrition, 43:6, 823-833, DOI: 10.1080/01904167.2020.1711941


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