40 Years of Organic Green Manure for the Win

A new study finds:

  • Organic Green Manure and Organic Animal Manure treatments increased cumulative water infiltration by about 10 times compared with the conventional farming treatment
  • Soil aggregates increased by 50% with the Organic Green Manure and by 30% with the Organic Animal Manure treatments in the upper 15-cm depth
  • At the same depth, bulk density was 3% lower under organic practices than in the conventional farming treatment, suggesting that organic farming reduces the soil’s susceptibility to compaction.

Organic Farming and Soil Physical Properties: An Assessment after 40 Years


Soil Carbon Aggregate Dynamics

The distribution of 13C-glucose in soil aggregate fractions during incubation. Different lowercase letters denote significant differences at P < 0.05 between sampling dates under the same treatment, and different captical letters denote significant differences at P < 0.05 between treatments on the same sampling date.

Soil aggregate dynamics involves aggregate formation, stabilization and breakdown processes, largely controlled by biological processes in soil and their interaction with physical processes such as wetting/drying, thawing/freezing, and tillage. Although considerable research has explored soil aggregate dynamics, the life cycle of an aggregate and its impact on microbial mediated C cycling remains elusive.

New short-term aggregate dynamics research[1] has found

The new C was accumulated more but decomposed faster in macroaggregates than in microaggregates. A positive relationship was observed between the 13C concentration in aggregates and the aggregate turnover rate (P < 0.05). The relative change in each aggregate fraction generally followed an exponential growth over time in the formation direction and an exponential decay in the breakdown direction.

Greater 13C concentration in 2–5 mm and 0.25–2 mm fractions compared to the <0.25 mm fraction indicates that the new C was more readily accumulated in macroaggregates than in microaggregates. This is likely due to the rate of glucose movement into macroaggregates through large pores that are available in comparison to microaggregates.

The negative values of the relative change in 2–5 mm aggregates over time with or without 13C-glucose addition in the breakdown direction indicates progressively less breakdown and hence stabilization of this fraction compared to the initial condition.

The new C input decreased the breakdown of all sizes of aggregates and increased their formation rate.

In the formation direction, the newly formed aggregates exponentially increased with time, with larger aggregates forming faster than smaller ones.

The aggregate stability increased greatly immediately after C input as glucose and then slowed down with the further decomposition of this added substrate.

[1] Combined turnover of carbon and soil aggregates using rare earth oxides and isotopically labelled carbon as tracers http://www.sciencedirect.com/science/article/pii/S0038071716304606

The Subsoil Watering Wand – Fertigation and Aeration in One Action?

Wiser Watering

Results now or your money back!

I’ve often wondered how well fertigating plants simply by mixing soil and water well regularly would perform…

You are after all helping to dissolve soil nutrients into the water for soluble nutrient loving plant roots to take up.

Notice how much soil disturbance this subsoil watering wand creates. The murky water is effectively fertigating the plant and aerating the soil all in one action.

That’s great right?

A while ago, before I knew better, I came up with the idea of using an ultrasonic cleaner filled with water and soil to fertigate with. You ultrasonically shake the soil to bits to dissolve the nutrients and then water it on. Part of me still wants to perform that experiment…

However I have a few concerns with any soil disturbance method. The first includes the break down of organic structure of the soils. You can see clods forming large aggregates on the surface of bare soil in the wand video. This tends to happen in soil deficient in organic matter and also calcium as it leaches away and the clay particles bind to one another. Sulfur and boron among others tend to leach as well.

By constantly destroying the soil structure you destroy microbe homes and the microbial exudates that hold soil particles together. Small colloids that become suspended in the water either then end up together or at the top of the soil and will often create a soil crust or large clods when they dry out. Take a look at the classic jam jar soil shake test below and see what I mean. Up top you have organic matter floating, followed by clay, silt and sand particles at the bottom. That organic matter dries in the sun above a layer of clay and ends up oxidising away into the atmosphere, or if you’re lucky becomes food for the subsurface microbial survivors in that clay. The clay then forms a barrier, water won’t penetrate and instead runs off or sits on the surface and then evaporates.


Heavy rain can also create a similar problem in dispersive soils with mineral imbalances.

Notice how dry the top soil was. It has no structure, no organic matter, it will hold little water. That’s unproductive soil. The most valuable soil, the layer at the edge between air and soil with the most aeration, is going to waste.

That soil could benefit from mulching.

Chop, throw, drop.