Coming out of a record-setting warm winter season, those involved with gardens and lawns should consider how our soils and soil fertility have been impacted by this past winter’s unusual temperatures and moisture patterns. So, what soil processes and conditions have been affected by this past winter?
Moisture levels
To understand how our current weather patterns can impact our garden soil, we need to look at the role that soil moisture might play. After gardens and lawns end their season (either harvest or dormancy), recharging soil moisture becomes a significant issue as the plants have used soil moisture throughout the growing season. When plant growth ends or subsides, the goal is to have precipitation go into the soil and fill soil pores.
Fall rains can be very effective for recharging soil moisture. But when the soil freezes, most additional rain or snow does not enter the soil. This moisture will probably run off during the late winter or spring thaw.
In areas that received sufficient rainfall, the amount of precipitation entering the soil has been much greater due to the record-setting winter warmth and minimal frost conditions. In drier regions of the state, this only pertains to the potential for soil moisture recharge.
Fertility: microbes and nutrients
How can such a mild winter affect soil fertility? While temperature influences soil's physical and chemical properties, its effect is relatively insignificant. However, biological properties and processes are greatly affected by temperature.
Consider all the microbes that live in our soils and the work they do decomposing organic materials (plant residue, compost, manures, leaves, etc.) that are added to the soil. As a rule of thumb, for every 18°F increase in temperature microbial activity doubles. As there is essentially no activity in frozen soil, this winter has benefitted the microbes in our soils, composting piles and containers.
The microbes were more active in the soil and decomposed more in the past few months than normal. This results in more nutrients being available for plants to take up in the next growing season.
Keep in mind that the nutrients of most significance in organic material decomposition from a soil fertility perspective are nitrogen (N), phosphorus (P) and sulfur (S). So all the nutrients from the existing soil organic matter and added organic amendments will have some extra, positive effect this growing season — assuming they are not lost.
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Categories: Minnesota, Weather