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Soil Testing & Interpretation
Dustin Harrell Research Agronomist & Rice Extension Specialist Louisiana Soil Health and Cover Crop Conference January 23-24, 2018
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Different Approaches to Soil Sampling
The field Conventional sampling Grid Sampling Sampling by management zone
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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
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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
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>85% 84-60% 59-40% 39-20% <20%
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Some soil tests work better on certain soils (are calibrated for)
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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.
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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
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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
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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)
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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
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LSU AgCenter Rice Extension Specialist
Thank you Dustin Harrell LSU AgCenter Rice Extension Specialist (337)
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