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

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

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

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

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

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

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.

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

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

Nutrient Uptake & Removal by Rice 200 bu (9,000 lb or 55.6 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)

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

LSU AgCenter Rice Extension Specialist Thank you Dustin Harrell LSU AgCenter Rice Extension Specialist dharrell@agcenter.lsu.edu (337) 250-3553