When MANAGING for soil carbon really pays

September 27, 2013
By Chad Kruger

In August I published a post describing one mechanism by which increasing soil organic carbon (SOC) can lead to direct financial benefit on irrigated farms. In that particular example, the agronomic value of the carbon could be more than 10X greater than the potential value of a “carbon credit”.  While it’s clear that there are general benefits to increasing SOC, in reality the specifics of each situation, such as the climate, soils, and management system, will all have an impact on monetizing any benefit. In this post I’ll examine a different case example published by some of my colleagues working at the WSU Cook Agronomy Farm, a dryland wheat farm near Pullman, Washington.

In dryland production, farmers are dependent on the moisture that falls from the sky to grow their crops. Because they can’t “cheat” by supplementing with irrigation water, precipitation literally drives every management decision the farmer makes. Therefore, local production systems (crop selection, rotation, tillage, fallowing practices) evolve to fit local precipitation regimes (amount and timing). In the U.S. Pacific Northwest, our Mediterranean climate pattern means that we receive the majority of our precipitation during the winter — the off-season for crop production. Our entire wheat production system has evolved around the need to farm with “stored winter moisture” – which explains why our predominant crop is winter wheat (planted in the fall to take full advantage of winter moisture).

With this context, two factors seem intuitive: 1) Soils with higher SOC should “store more moisture” just like they do on irrigated farms and 2) what happens to winter precipitation is an important factor in determining the success of a crop. For those of you not familiar with the Palouse, I’ll briefly explain the unique nature of how these two factors play out. First, the extreme topographical heterogeneity (a.k.a. big, rolling hills) creates a fairly significant distribution of SOC levels (ranging from lows below 1% SOC on ridge-tops to highs of near 5% SOC in the valleys). Second, the climate of the Palouse is such that winter temperatures often fluctuate around the freezing line, leading to a combination of freezes and thaws where winter precipitation falls as snow, but can be rapidly redistributed across the terrain both as blowing snow and meltwater runoff. In light of the unique character of these factors in the Palouse, it makes sense that different parts of a field will hold moisture better than other parts, and consequently will produce higher (valleys and north slopes) and lower yields (ridge tops and south slopes) – see the image below.

Figure 1. Patterns of wheat senescence due to landscape and soil controls over soil water.

Figure 1. Patterns of wheat senescence due to landscape and soil controls over soil water.

Figure 2. Relative yield of winter wheat at the WSU Cook Agronomy Farm.

Figure 2. Relative yield of winter wheat at the WSU Cook Agronomy Farm.

So what influence can improved agronomic management have on increasing the water storage capacity of a Palouse farm? My USDA colleague Dave Huggins and his research group set out to answer that question in the middle of a snowstorm. They measured snow fall, distribution and snow water equivalents on the Cook Agronomy Farm managed under no-till and a neighboring field managed under conventional tillage. No-till is generally promoted as a strategy for increasing SOC because it does not disturb the crop residues (a.k.a. carbon inputs), but instead leaves the crop stubble standing in the field to decompose naturally, providing a cover of straw that reduces potential erosion and provides a food source for soil microbes. Huggins’ team found that the residue cover in the no-till field had a profound effect on the distribution of snow, recharge of the soil water profile and potential for increasing yields (see table 1).

Table 1.

Conventional Tillage

No-till w/ residues

Potential Yield increase (bushels / ac)   for No-till

Snow depth (cm) CT

Snow depth (cm) NT

Soil moisture (mm) increase over CT

South Slope

18

28

+29

+6

Ridge top

11

23

+60

+13

Valley

28

33

+13

+3

The research team indicated that the standing residue limited the redistribution of snow across the landscape and increased the infiltration of water into the soil, creating more uniformity in the distribution and storage of moisture through the field than conventional tillage. While the undisturbed residues alone likely don’t fully explain the increased moisture available (higher SOC levels due to long-term no-till management likely play a role), it’s clear that they had a significant and favorable effect and that management strategies that leave residues undisturbed could have important implications for the profitability of the farm.

From prior research we can estimate that the “carbon credit” value of the no-till system might range from $15 – 30/acre over the past decade (using $5 -10/ton of CO2e range). Huggins’ team estimated that the potential increase in yield due to more uniform distribution of snow-water equivalents could average $30/acre across the field in a single year, with profits on ridge-tops increasing by more than $50/acre. Like we saw under irrigation, that’s real money in the SOC bank!

 

 

Qiu, H., D.R. Huggins, J.Q Wu, M. E. Barber, D.K. McCool, and S. Dun. 2011. Residue management impacts on field-scale snow distribution and soil water storage. American Society of Agricultural and Biological Engineers, Vol. 54(5): 1639-1647

 

One comment on “When MANAGING for soil carbon really pays”

  1. Maurice Robinette said on September 27, 2013:

    I wonder what the carbon value would be with something besides SOC and residue in place,like a fully functioning biodiverse ecosystem. Similar to what was in place on the Palouse prior to cultivation. Can you even estimate that with some accuracy? What kind of root structure would be necessary to hold the soil in steep slopes for thousands of years? How much carbon is that? And most importantly, how many people would be fed with the number of cows necessary to duplicate and sustain such a process? What if that number were greater than the people eating noodles from the Palouse today? Enough questions?

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