How to Turn a Soil Test Lime Recommendation Into an Application

Why this matters

A soil report that says "apply 70 lb of limestone per 1,000 sq ft" is not yet an application. Between that line and a lawn there are four decisions a tech can get wrong: what kind of lime the number assumes, how much of the shop's actual product equals it, how many passes it takes, and what spreader setting puts it down. Get the product equivalence wrong and the pH never moves, so next year's report asks for the same lime again and the customer wonders what they paid for. Dump the whole rate in one pass on established turf and it sits on the surface for months. This card is the shop's one method for turning the report line into bags, passes and a setting.

Why the lab arrived at that rate, from the soil pH and the buffer pH, belongs to 'Buffer pH and Why the Lime Rate Follows It'. Taking the sample belongs to 'Soil Test Collection and Interpretation'.

Step 1: Read exactly what the report is recommending

Three things on the report decide the math, and they vary between labs:

• The unit. Pounds per 1,000 square feet is the norm on turf reports, but agricultural labs often report tons per acre. To convert, multiply tons by 2,000 to get pounds per acre, then divide by 43.56 (thousands of square feet in an acre). A 1.5 ton per acre recommendation is 3,000 / 43.56 = 68.9 lb per 1,000.
• The material basis. Many reports state the rate as pure calcium carbonate, or as agricultural limestone of a stated neutralizing value. Your bag lists its own calcium carbonate equivalent (CCE), the neutralizing power compared with pure calcium carbonate. If the report's basis and the bag's CCE differ, the product rate changes.
• The kind of lime, if stated. Reports often call for dolomitic lime when soil magnesium is low and calcitic lime when it is adequate or high. Use the kind the report calls for; the rate math is the same either way.

Why read before computing: a report written on a 100 percent basis and a bag at 90 percent CCE are 11 percent apart. Applied as if they were the same, the lawn gets 90 percent of the neutralizing power the lab asked for, every application, and the shortfall only shows on the next test.

Step 2: Convert to your product

Divide the report rate by the bag's CCE as a decimal, if the report is on a pure calcium carbonate basis:

• Report: 70 lb per 1,000, pure calcium carbonate basis.
• Bag: pelletized calcitic lime, CCE 90 percent.
• Product rate: 70 / 0.90 = 77.8 lb per 1,000.

If the report states a different basis, divide by the ratio of your CCE to that basis instead. If the report gives no basis at all, call the lab or read its interpretation notes rather than guessing.

Pelletized is not stronger. Pelletized lime is finely ground limestone bound into granules so it spreads cleanly. Pound for pound it neutralizes the same as the ground limestone it was made from, at the same CCE. Fine grinding makes lime react faster, but it does not change how much the soil needs. A rate cut because "pellets are concentrated" leaves the pH short.

Step 3: Split the rate into passes

On established turf, apply no more than about 50 lb of lime per 1,000 square feet in a single application, which is the commonly cited ceiling; a heavier rate goes on in two or more passes, weeks or months apart. 77.8 is over 50, so it splits into two passes of 38.9 lb per 1,000.

Why split: lime moves down through soil slowly, and on established turf nothing works it in. A heavy single dose sits on the thatch and soil surface as a white layer, gets tracked into the house, can crust in rain, and pushes the pH of the top fraction of an inch much higher than the root zone below it. Two moderate passes let the first one start dissolving and moving before the second lands.

If the split per pass still exceeded 50, it would go to three passes. A 120 lb per 1,000 recommendation, for example, is three passes of 40.

The work-up for one lawn

A 6,000 square foot lawn, measured turf from the property record.

LIME WORK-UP - 6,000 SQ FT TURF
Report rec      70 lb per 1,000, pure CaCO3 basis
Product         pelletized calcitic, CCE 90
                40 lb bags
Adjusted rate   70 / 0.90 = 77.8 lb per 1,000
Total           77.8 x 6.0 = 467 lb
Passes          2 x 38.9 lb per 1,000 (cap 50)
Per pass        38.9 x 6.0 = 233 lb
Bags            467 / 40 = 11.7, load 12
Spreader        lime cal: setting 20 = 39.5 lb
                per 1,000
Pass 1          this visit, north-south
Pass 2          next visit, east-west
Retest          same time next year

Check the total from the other direction: two passes of 233 lb is 466, which matches 467 within rounding (the unrounded per-pass figure is 233.3). Twelve 40 lb bags is 480 lb, so 13 lb rides home. Each pass needs 233 / 40 = 5.8 bags, so load six bags for each visit and about 7 lb comes back each time.

Step 4: Calibrate the spreader for lime

Lime is a different granule from fertilizer, at more than ten times the rate, so the fertilizer setting means nothing here. Calibrate by weight over a measured strip the same way as for fertilizer, per 'How to Calibrate a Rotary Spreader by Weight Over a Measured Area', with two lime-specific changes.

• Use a shorter strip. At 38.9 lb per 1,000, a 2,000 square foot strip would use nearly 78 lb, more than many push hoppers hold. A 1,000 square foot strip uses about 39 lb, which most hold, and a scale reading to 0.1 lb is far finer than that.
• Run the pattern pans too. Pelletized lime is heavier than most fertilizer granules and throws differently, so the effective swath may not match the fertilizer swath. Space passes at the lime swath.

In the work-up, setting 18 used 34.0 lb over the 1,000 square foot strip (13 percent under the 38.9 target, since 34.0 / 38.9 = 0.87). Setting 20 used 39.5 lb, 1.5 percent over (39.5 / 38.9 = 1.015) and inside a 5 percent band of 37.0 to 40.8. Setting 20 goes on the lime card.

A second lawn, from a per-acre report

The same method on a report from an agricultural lab, to show where the two cases part ways. The report calls for 1.5 tons per acre of limestone on a pure calcium carbonate basis, and asks for dolomitic lime because soil magnesium tested low. The shop's dolomitic product is CCE 95 in 40 lb bags. The lawn is 3,200 square feet.

• Unit: 1.5 x 2,000 = 3,000 lb per acre; 3,000 / 43.56 = 68.9 lb per 1,000.
• Product: 68.9 / 0.95 = 72.5 lb per 1,000.
• Passes: 72.5 is over 50, so two passes of 36.3 lb per 1,000.
• Total: 72.5 x 3.2 = 232 lb, or 116 lb per pass. Bags: 232 / 40 = 5.8, load six.

The dolomitic product is a different granule from the calcitic one in the first work-up, so it gets its own lime calibration run and its own setting; setting 20 belongs to the calcitic product only. The trap on this report is the unit: a tech who reads "1.5" as pounds per 1,000, or applies 1.5 tons as if it were per 1,000, is off by a factor of about 45 in one direction or the other.

Step 5: Time the passes

Lime can go on whenever the ground is not frozen and the turf is not waterlogged, and fall is a common choice because freeze-thaw and fall rains help move it into the soil over winter. The second pass goes on at a later visit: commonly the next round on a four-to-eight-week program, or the following season for a lawn on fewer visits. Running the second pass at a right angle to the first evens out any banding from the spreader.

Two timing conflicts to avoid on the same visit:

• A urea-based feeding. Urea loses nitrogen as ammonia gas faster on a high-pH surface, and a fresh lime layer raises the surface pH. Water the feeding in, or put the lime and the feeding on different visits.
• Seeding into established turf. Lime does not hurt seed, but the visit that carries the seed often carries a starter fertilizer, and the same urea point applies. See related: 'Fall Core Aeration & Overseed' for where lime sits in that program.

What changes the answer

• Bare soil before seeding or sodding. With no turf in the way, the full rate can go on at once and be tilled into the top several inches, which puts the lime where the roots will grow. The 50 lb cap is about established turf.
• A product with a different CCE. A ground limestone at CCE 100 against the same 70 lb report is 70 lb per 1,000: still over 50, still two passes, at 35 lb each.
• A recommendation under the cap. A report calling for 30 lb per 1,000 at CCE 90 is 33.3 lb per 1,000, one pass.
• A report asking for sulfur instead. That is a high-pH soil and a different card; do not apply lime against a high pH because the program calendar says "lime in fall."

How to know it worked

Lime works over months, so the first honest check is the next soil test, taken the same way, at the same time of year, from the same areas. Compare the soil pH and the buffer pH with this year's. A pH that has moved toward target and a smaller or no lime recommendation means the program is working; a pH that has not moved means check the product equivalence, the spreader card for lime, and whether both passes actually went on. The property record should show both passes with dates, rates, settings and who applied them.

References

• The soil testing lab's report and interpretation notes for the rate basis and units.
• The lime bag's label for calcium carbonate equivalent and material type.
• See related: 'Soil Test Collection and Interpretation'
• See related: 'Buffer pH and Why the Lime Rate Follows It'
• See related: 'How to Calibrate a Rotary Spreader by Weight Over a Measured Area'