1. Soil Testing & Interpretation
Dustin Harrell
Research Agronomist & Rice Extension Specialist
Louisiana Soil Health and Cover Crop Conference
January 23-24, 2018

2. Different Approaches to Soil Sampling
The field
Conventional sampling
Grid Sampling
Sampling by management zone

3. Soil analysis air dried, ground, sieved
Soil test extraction used to provide an “Estimate of plant available nutrients”
Extracts portions of many different forms of nutrient
Organic & inorganic

4. Soil analysis Soil test interpretation ranges developed
Very high, high, medium, low, very low
Provides a probability of expected response
# meaningless unless correlated & calibrated
Relationship to crop response determined from field trials.
Set of soils:
grouped by soil texture & soil pH
multiple fertilizer rates

5. >85%
84-60%
59-40%
39-20%
<20%

6. Some soil tests work better on certain soils (are calibrated for)

7. Where do fertilizer recommendations come from?
Come from long term calibration trials
Changes necessitate continuation of calibration trials
hybrids/varieties
tillage systems
yield potential
Labs doing analysis do not always make recommendations
Consultants
CPS, Helena, Pinnacle (Sanders/G&H), GreenPoint, etc.
Extension/Scientists
Producers
Modified based on grower information
Fertility goals, land ownership, financial situation, fertilizer placement, etc.

8. Fertilizer recommendation Approaches
Sufficiency Approach
Apply just enough to maximize profitability in the year of application only
Based on soil test calibration field data
Same from year-to-year
Calibrated to 90 or 95% max yield
Rates are highest at “very low” and increase to nothing at critical level
(95%max yield; “high” category)
LSU AgCenter Recommendations

10. Fertilizer recommendation Approaches
Build-maintenance Approach
Apply enough meet needs and build levels to non-limiting level (critical level)
Once level is built up to non-limiting level, fertilizer is added to “maintain” level
4-8 years
Disadvantage: rates are generally higher than sufficiency approach

12. Nutrient Uptake & Removal by Rice
200 bu (9,000 lb or bbl)
Nutrient Uptake
P2O5: 76 lbs/A
K2O: 220 lbs/A
Nutrient Removal
P2O5: 60 lbs/A (79%)
K2O: 32 lbs/A (15%)
Often Maintenance Recommendation
Build + Maintenance
Calculation varies
Generally some variation of
Yield goal maintenance
% of uptake
- soil availability
Many models (depends on who is giving the recommendation)

15. LSU recommendation is variety based
200 bu/A requires approximately :
115 lb N – 32 lbs available = 82 lbs
LSU recommendation is variety based
120 – 160 lbs N/A

16. LSU AgCenter Rice Extension Specialist
Thank you
Dustin Harrell
LSU AgCenter Rice Extension Specialist
(337)