Soil Science

Background

Soil quality is essential for successful agriculture and in our context for optimally raising blueberries.  In my view, soil is not simply a medium in which plants grow, but rather soil is an entire ecosystem that contains numerous living creatures, decomposing material, inert material, and essential elements.  Sometimes soils are treated to provide the essential nutrients or elements for optimal plant production, i.e. is there enough nitrogen and phosphorus in the soil.  My question is more along the lines of providing nutrients for the soil environment and optimizing conditions for the "web of life" in the soil.  If the soil is healthy, then the plants growing in it will prosper.

Soil quality can be determined by a minimum data set of physical, chemical, and biological indicators.  The physical indicators can be determined by the water holding capacity, the depth of the soil, the infiltration, and the soil texture.  The chemical indicators include the organic matter (which influences fertility and stability), the pH (defines thresholds of chemical and biological activity, e.g. blueberries need an acid soil with a pH of 4.5-5.0), the electrical conductivity (influences activity thresholds of plant and microbes), and extractable elements: nitrogen, N; phosphorus, P; and potassium, K.  In addition numerous micro-elements are also essential.  The biological indicators include the microbial biomass carbon and nitrogen, the potentially mineralizable nitrogen, and the respiration level (defines a level of microbial activity and provides an estimate of biomass activity).

 

Context at Knoll Acres

The above map shows the general location of the two blueberry plots at Knoll Acres.  The organic plot is colored green and the traditional plot is colored orange.  The "white" structure between the plots is our house.  Thus the traditional plot is located northeast of the house, is sloped on the side of a hill, and has an elevation of about 10 feet.  The rows are laid out from north to south.  The organic plot is located southwest of the house.  It also lies on a hill slope with an elevation of 10-15 feet from one side to the other.  The rows are laid out in the north to south direction.

Based on the descriptions in the soil map book of Rockingham County, the soil type of this plot (31D2) is called Frederick and Lodi cherty silt loams, 15-25 percent slopes, eroded.  The following paragraphs are taken from the Rockingham County Soil Map book and further describe this soil type.

This unit consists of moderately steep, well drained soils on the side slopes of hills and ridges.  The areas range from about 3 to 100 acres.  Some areas have shallow drainage ways 100 to 300 feet apart.  Some areas of this unit consist mostly of Frederick soils, some mostly of Lodi soils, and some of both.  The Frederick and Lodi soils were mapped together because they have no major differences in use and management.  The total acreage of this unit is about 45 percent Frederick soils, 40 percent Lodi soils, and 15 percent other soils.

Typically, the surface layer of the Frederick soils is brown cherty silt loam about 7 inches thick.  The subsoil extends to a depth of 60 inches or more.  Between depths of 7 and 13 inches, it is strong brown clay loam.  At a depth of more than 13 inches, it is yellowish red and red clay.

The surface layer of the Lodi soils is a dark grayish brown cherty silt loam about 7 inches thick.  The subsoil is strong brown and yellowish red silty clay loam and clay 53 inches thick.  The substratum is brownish yellow silty clay to a depth of 72 inches or more. 

Included with these soils in mapping are small intermingled areas of Edom, Swimley, and Timberville.Variant soils that make up about 10 percent of this unit.  The Edom and Swimley soils are on the uplands adjacent to the Frederick and Lodi soils.  The Timberville Variant soils are in low areas along drainageways.  Also included are small areas of soils with a surface layer of silt loam, spots of very cherty soils, sinkholes, small areas of exposed bedrock, and spots of severely eroded soils.  These make up about 5 percent of this unit.

The permeability and available water capacity of these Frederick and Lodi soils are moderate.  Surface runoff is rapid.  The soils are low in natural fertility and organic matter content.  The shrink-swell ptential of the subsoil is high in the Frederick soils and moderate in the Lodi soils.  The root zone extends to bedrock.  Both soils are strongly acid or very strongly acid.

Slope makes these soils poorly suited to cultivated crops.  These soils are moderately well suited to pasture and hay.  Much of the acreage is farmed.  The hazard of erosion is very severe and is a major management concern.  Establishing and maintaining a mixture of grasses and legumes and the prevention of overgrazing are the main pasture management concerns.  Use of proper stocking rates, pasture rotation, and deferred grazing are practices that help to maintain pastures and control erosion.

The soils of this unit are well suited to trees, but only a small acreage is wooded.  Potential productivity is high.  The soils are managed for hardwoods and pine.  Slope is the main limitation of these soils for community development.  The capability subclass is IVe.

From my perspective as a landowner, I think the above description is fairly accurate.  From 1991 (when we purchased this land) until the summer of 2008, this plot was pasture for sheep, goats, cattle, and horses.  Recognizing the native acitdity of this soil, I applied lime and commercial fertilization to this area several times during the past twenty years.  Most recently during the spring of 2008, I applied a fairly heavy treatment of lime and a light treatment of general purpose fertilizer (10-10-10) to this area.  Later that summer, I decided to use this plot to plant organic blueberries and recognized that it will take some time and effort to lower the pH, increase the humus and organic matter in this soil, and to "overcome" the effects of the commercial fertilizer.

The above photo map is a satellite view of the organic blueberry plot at Knoll Acres.  The approximate location is indicated with the heavy line.

Organic Blueberry Plot Rows, View from the south.  Rye cover on rows. April 2009

Conventional Blueberry Plot, view from the north.  Rye cover crop on rows.

Fall 2008

In September 2008, I decided to raise organic blueberries on this plot.  This plot is on a hillside with a slot facing the south-west.  Formerly this area was native pasture land.  According to the USDA Soil Map this ground is "Frederick and Lodi gravelly silt loam soil with 15-25% of the slopes eroded."

During the spring of 2008 (before we decided to raise blueberries here), I had applied lime and a small amount of commercial fertilizer (10-10-10) to this area to enhance the pasture growth!  That was an attempt to raise the soil pH to a more neutral place so that pasture grass would grow better.  However, that was the wrong thing to do for blueberry production, since blueberries need acidic soil.  During the early summer of 2008, we also did some excavation and put in the gravel lanes that border this plot of ground. 

Organic Blueberry Plot: Initial Soil Test Results

In August of 2008, I took a soil sample from this area (Organic Blueberry Plot) and sent it to the Virginia Cooperative Extension for analysis.  The following results were received on 8/25/08.

Analysis	P (lb/A)	K (lb/A)	Ca (lb/A)	Mg (lb/A)	Zn (ppm)	Mn (ppm)	Cu (ppm)	Fe (ppm)	B (ppm)
Result	56	381	3882	324	4.8	43.9	0.9	5.9	0.5
Rating	H	VH	VH	VH	SUFF	SUFF	SUFF	SUFF	SUFF

Analysis	Soil pH	Buffer Index	Est.-CEC (meq/100g)	Acidity (%)	Base Sat. (%)	Ca Sat. (%)	Mg Sat. (%)	K Sat. (%)	Organic Matter  (%)
Result	6.6	6.50	11.5	0.3	99.7	84.0	11.6	4.2	not done

Recommendations from Virginia for this plot in planting blueberries were "apply a total of 150 lb N/Acre of fertilized band in three applications beginning in early April (75 lb/A) with subsequent applications (37.5 lb/A + 37.5 lb/A) at 5 week intervals.

Conventional Blueberry Plot (Not-organic): Initial Soil Test Results

This blueberry plot is located east of our garden on a grassy slope.  Immediately to the north is the edge of an oak woods.  To the south the plot ends near the place where we planted our original blueberries (six plants, three cultivars) about five years ago.  We took an initial soil sample at this plot also in August of 2008 and sent it to Virginia Cooperative Extension for analysis.  Their soil test report for this Traditional Blueberry Plot follows:

Analysis	P (lb/A)	K (lb/A)	Ca (lb/A)	Mg (lb/A)	Zn (ppm)	Mn (ppm)	Cu (ppm)	Fe (ppm)	B (ppm)
Result	296	206	4639	682	16.3	26.7	0.1	5.5	0.9
Rating	VH	H-	VH	VH	SUFF	SUFF	SUFF	SUFF	SUFF

Analysis	Soil pH	Buffer Index	Est.-CEC (meq/100g)	Acidity (%)	Base Sat. (%)	Ca Sat. (%)	M Sat. (%)	K Sat. (%)	Organic Matter (%)
Result	6.9	6.51	14.7	0.2	99.8	78.9	19.1	1.8	not done

Recommendations from Virginia for this plot in planting blueberries were "apply a total of 150 lb N/Acre of fertilized band in three applications beginning in early April (75 lb/A) with subsequent applications (37.5 lb/A + 37.5 lb/A) at 5 week intervals."

Establishment of Blueberry Rows

During September of 2008, we laid out the blueberry rows on both the Organic Plot and the Traditional Plot.  Rows were put on eight foot centers and oriented in the North-South direction.   We cultivated four foot strips using a disk plow with several passes to work up the soil.  Then we ran the subsoiler twice through the row centers at depths ranging from 12-24 inches.

This activity of stirring the ground brought up a lot of rocks to the surface.  We spent a lot of time picking up and removing rocks.  Typically a tractor scoop load per row.

The Organic Plot had 14 rows ranging from 64-20 ft lengths, average length was 50 ft.  These rows were designed for 156 plants placed at 4.5 ft intervals.  The Traditional Plot had 4 rows ranging from 24-12 ft lengths, average length was 19.5 ft.  These rows were designed for 19 plants placed at 4.5 ft iintervals.

Treatment of Rows: Elemental Sulfur and Rye Cover

In September 2008, we broadcast 50 lb of sulfur on all the blueberry rows which approximated about 1 lb sulfur / 47 sq ft.  This was an inadequate treatment; we should have tripled this amount.  Then we rototilled the rows with a motorized rototiller, picked up rocks, and broadcast annual ryegrass seed on the rows as a cover crop for the winter.

Spring Row and Soil Treatments and Tests

In April 2009, we mowed the ryegrass and grass row middles several times.  We took new soil samples for analysis: two from the organic blueberry plot and one from the traditional blueberry plot.

The soil test results (4/30/09) were as follows:

Sample ID	Analysis	P (lb/A)	K (lb/A)	Ca (lb/A)	Mg (lb/A)	Zn (ppm)	Mn (ppm)	Cu (ppm)	Fe (ppm)	B (ppm)	Sol Salts (ppm)
Trad BB Rows 1-4	Result	167	315	5282	424	7.3	47.5	0.1	5	0.8	269
	Rating	VH	VH	VH	VH	SUFF	SUFF	SUFF	SUFF	SUFF	L
Org BB Rows 1-4	Result	107	451	4771	351	6	42.1	0.1	4.7	0.6	230
	Rating	H+	VH	VH	VH	SUFF	SUFF	SUFF	SUFF	SUFF	L
Org BB Rows 7-9	Result	38	223	1911	198	3.2	35.2	0.2	4.1	0.4	115
	Rating	H-	H	H	H+	SUFF	SUFF	SUFF	SUFF	SUFF	L

Sample ID	Soil pH	Buffer Index	Est. CED (meq/100g)	Acidity (%)	Base Sat. (%)	Ca Sat (%)	Mg Sat (%)	K Sat (%)	Organic Matter (%)
Trad BB Rows 1-4	7.2	N/A	15.3	N/A	100	86	11.4	2.6	8.8
Org BB Rows 1-4	7.6	N/A	13.9	N/A	100	85.5	10.4	4.1	5
Org BB Rows 7-9	6.8	6.46	5.9	0.7	99.3	80.7	13.8	4.8	4

Recommendation from Soil Test Lab: "Apply a total of 150 lb N/Acre of fertilized band in three applications beginning in early April (75 lb/A) with subsequent applications (37.5 lb/A + 37.5 lb/A) at 5 week intervals; soluble salts are not high enough to cause salt injury."

During the months of May & June we had a lot of rain which made it impossible to work the blueberry row ground.  When the ground dried toward the middle of June, I mowed the rye again and then I used a chisel plow (four shafts) with the outside ones set at a distance of 40 inches.  I tilled the rows twice, breaking up the ground and the rye panting.  Near the end of June 2009, after another round of picking up rocks, I applied compost to the soil rows in the following way:

• Conventional Blueberry Rows A-D: Horse manure/sawdust compost
  • Tried to cover the row with a layer of compost
• Organic Blueberry Rows A-D: Horse manure/sawdust compost
  • Tried to cover the row with a layer of compost
• Organic Blueberry Rows E-H: Sheep manure/hay-straw compost
  • Tried to cover the row with a layer of compost
• Organic Blueberry Rows I-J: Pine needles (not composted)
  • Put a total of five bales of pine straw on these two rows and tried to incorporate the pine straw into the soil with the rototiller.  That didn['t work since the straw clogged up the rototiller. 
  • Then I re-gathered the pine straw and ran it through the wood chipper and re-spread the mulched pine straw on the rows.  After chipping, it worked to incorporate that material into the soil with the tiller.
  • Also applied 7 bags of shedded pine bark mulch to these two rows (about 1 cubic ft/22 sq ft of row).
• Organic Blueberry Rows K-N: "Planter's Choice Compost" from Wood Ridge Dairy
  • Spread two scoops of compost on these short rows.

Summer Row and Soil Treatments

On July 4, 2009, we added soil amendments to the Blueberry Rows according to the following guide:

Amendment	Unit/Bag	Description	Rate	Treatment Comment
Azomite (volcanic mineral and trace elements)	44 lb / bag	Important for plant nutrition and growth; apply with compost and manures	3.5 lbs / 100 sq ft	Treated all rows (2,352 sq ft total) used two bags
Blood Meal	50 lb / bag	Provides nitrogen	Side dress at 2 lbs / 100 sq ft	Treated organic rows I & J with 3 lbs / row (306 sq ft total) use partial bag
Fish Meal	50 lb / bag	Stimulates bio activity and increases tilth	2 lb / 100 sq ft	Treat all rows (2,352 sq ft total) use 1 bag
Rock Phosphate	50 lb / bag	20% total phosphate; 7% phosphoric acid and 23% calcium	2 lb / 100 sq ft	Treat all rows (2,352 sq ft total) use 1 bag
Green sand (ocean deposite iron-potassium silicate; 7% potash and 30+ trace minerals)	50 lb / bag	looses soils and catalizes release of additional nutrients from soil	4 lbs / 100 sq ft	Treat all rows (2,352 sq ft total) use 1 bag
Holly Tone	27 lb / bag	acid fertilizer	5 lbs / 100 sq ft	Treat all rows (2,352 sq ft total) use five bags
Peat Moss	3.8 cu ft / bag	acid soil amendment & growing medium	2 cu ft / 100 sq ft	Treated all rows (2,352 sq ft total) used 12 bags

Soil Amendment Source:  Peat Moss was obtained from Lowe's; the other organic materials were purchases from Seven Springs Farm, 426 Jerry Lane NE, Check, VA 24072 (Floyd County).

On July 6, 2009, applied 12 bags of shredded bark mulch to all rows at a rate of 1 cu ft mulch / 100 sq ft.  Source of shredded bark mulch was Lowe's.  Then ran the chisel plow through all the rows twice more.  Plowed uphill rather than down hill to minimize movement of soil.

During the middle to end of July, worked with Jeremiah Vallotton to construct raised bed borders for a portion of each of the first eight organic rows (A-H).  This consisted of screwing two oak boards together via side slats creating a bed border height of about eleven inches.  The sides were constructed 3 feet apart with a reinforcing frame board connecting the two sides.  (See the photograph below.)  Square oak stacks were driven into the ground beside the edges; the edge boards were then screwed to the stake boards.

Oak wood raised bed borders constructed July 2009.

EMU Summer Bridge Students Test Knoll Acres Blueberry Soil

On July 28, 2009 Seven EMU Summer Bridge Students visited Knoll Acres to test various organic blueberry plots.  Along with Jeremiah Vallotton, the students were randomly placed into four teams of two and were given responsibility to sample a specific organic blueberry plot and compare it with another organic blueberry plot.  The organic plots and the names of the students with their assignments follow:

• Sample the Horse Manure & Sawdust compost plot (rows A-D) and compare it to the Planter's Choice compost plot (rows K-M): Anca Chirvasuta & Jeremiah Vallotton
• Sample the Sheep Manure & Hay compost plot (rows E-H) and compare it to the Horse Manure & Sawdust compost plot (rows A-D): Tim Gautsche & Phillip Martin
• Sample the Pine Straw compost plot (rows I-J) and compare it to the Sheep Manure & Hay compost plot (rows E-H): Karla Martin & Alejandra Guitierrez
• Sample the Planter's Choice compost plot (rows k-M) and compare it to the Pine Straw compost plot (rows I-J): Aly Zimmerman & Zachery Ferguson

For a map describing these rows go to the Project Design page on this website and scroll down to the section on Plot Plans.

../Project Design/projectdesign.htm

Student teams were assigned to complete two in-field respiration and water infiltration tests on their assigned sample plot, using the USDA Test Kit protocols.  They also took four soil samples from their assigned plot and transported it back to the laboratory for further analysis using the LaMotte Test Kit protocols.  While there were some variations in running the various tests, the following table summarizes their results.

 

In-Field Soil Tests with USDA Kit		July 28, 2009	EMU Summer Bridge	Student Work
Compost Group	Num	Respiration (lbs CO2-C/acre/day)	Water Infiltration (in/hr)	Soil Temp (⁰C)
Horse Manure & Sawdust compost rows (A-D)	2	122	199	24
Sheep Manure & Hay compost rows (E-H)	2	61	88	34.6
Pine Needle compost rows (I-J)	2	67	158	31.1
Planter's Choice compost rows (K-N)	1	60	300	30.3
Average		78	186	30.0

LaMotte Lab Soil Tests			July 28, 2009				Summer Bridge	Student Work
Compost Group	Num	pH	Nitrate Nitrogen (ppm)	Nitrite Nitrogen (ppm)	Ammonia Nitrogen (ppm)	Potassium (ppm)	Phosphorus (ppm)	Calcium (ppm)	Humus
Horse Manure & Sawdust compost rows (A-D)	4	6.9	144	1	5	250	100	2625	3.6
Sheep Manure & Hay compost rows (E-H)	4	6.6	50	1	5	160	100	2800	2.3
Pine Needle compost rows (I-J)	4	5.4	150	<1	5	203	88	n/d	n/d
Planter's Choice compost rows (K-N)	4	7.6	68	<1	5	n/d	22	n/d	2.3
Average		6.6	103	1	5	204	78	6475	2.7

In addition to the above values, several additional tests for micronutrients were done for the Organic Horse Manure & Sawdust compost rows with the following results:

• Sulfate (ppm): <50;
• Magnesium (ppm): 59;
• Manganese (ppm): 4; and
• Ferric Iron (ppm): 1

Selected Data from Four Soil Tests: 2008 - 2010

 

 

Related resources

• Soil quality information from the USDA Natural Resources Conservation Service USDA Soil Quality Indicators
• The Functional Value and Stability of Soil Resources is highlighted in this website by the NRCS National Soil Quality Team, Department of Natural Resources and Environmental Sciences, and the University of Illinois Functional Value of Soil Stability
• Soil Quality in an Organic Agricultural Systems is described by Iowa State University Extension Service in a PDF document Organic Soil Quality Indicators
• Organic Soil Quality indicators is also described in this PDF document by the Center for Environmental Farming Systems Soil Quality for Organic Farmers