3.8: Organic Matter and Cropping Systems
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- 25114
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Natural (virgin) soils generally have much higher organic matter levels than agricultural soils. But there are also considerable differences among cropping systems that can be generalized as follows: In a cash grain operation, about 55–60% of the aboveground plant biomass is harvested as grain and sold off the farm, thereby returning less than half of the mass of the aboveground plant to the soil. The nutrients removed in the crops are replaced through fertilizers, but the carbon is not. On dairy farms, on the other hand, the crops are commonly fully harvested as a forage and fed to the animals, and then most of the plant biomass, including nutrients and carbon, is returned to the field as manure. While most dairy farms also grow their own feed grain, some import grain from other places, thereby accumulating additional organic matter and nutrients. When considering a typical conventional vegetable operation, as with cash grain, much of the plant biomass is harvested and sold off the farm, with limited return to the land. But a typical organic vegetable system imports a lot of compost or manure to maintain soil fertility and thereby applies quite a lot of organic matter to the soil. They are also more likely to grow a green manure crop to build fertility for the cash crop.
A recent New York study analyzed soil organic matter levels and soil health for such distinctive cropping systems and found considerable differences (Table 3.3). Soils that were used to grow annual grain crops (corn, soybeans, wheat) averaged 2.9% organic matter and conventional processing vegetables averaged 2.7%. Dairy fields averaged somewhat higher levels (3.4%) and mixed vegetables (mainly small organic farms) averaged 3.9% organic matter. The highest organic matter levels, however, were measured for pastures (4.5%), where much of the plant is recycled as manure and the soil is not tilled. As a result of the soil management and organic matter dynamics, the physical condition of the soil is also impacted. Aggregate stability, which is a good indicator of the physical health of the soil, is greater when the organic matter content is higher and the soil is not tilled (Table 3.3).
| Table 3.3. Organic Matter Levels and Percent Soil in Water-Stable Aggregates Associated with Different Cropping Systems in New York | |||
|---|---|---|---|
| Cropping System | Description | Organic Matter (%) | Aggregate Stability (%) |
| Conventional vegetable | Intensive tillage; mostly inorganic fertilizer; crop biomass removed | 2.7 | 27 |
| Annual grain | Range of tillage; mostly inorganic fertilizer; crop biomass mostly removed | 2.9 | 30 |
| Dairy | Rotation with perennial forage crops; mostly intensive tillage with corn silage; crop biomass removed but mostly recycled through manure | 3.4 | 36 |
| Mixed Vegetable (mostly organic) | Intensive tillage; green manure and cover crops; mostly organic fertilizer like compost | 3.9 | 44 |
| Pasture | No-till; perennial forage crop; crop biomass mostly recycled through manure | 4.5 | 70 |