Nutrient Management

Chapter 16

BMPs for Soil and Water QualityBuffer stripsCover cropsConservation tillageRotations

FertilizersOrganicInorganic / synthetic

Limiting Factor

Plant and Soil Analyses for Nutrient Management

Methods of Fertilizer Application

Economic Considerations

Goals

Maximize return on nutrients

Maintain / improve soil quality

Protect water quality

Soil and Water Quality

BMPs

What’s this acronym, BMP?

Buffer strips

Grass or trees (and residue)

Particulate settlingChemical adsorption Chemical degradation

Increase or decrease in filter strip?

Increase, of course. Slowervelocity increases deposition.More organic matter in soil increases adsorption and the

soil environment is likely richer inmicrobes, increasing degradation rate.

Clear cut operation without SMZ Clear cut operation with SMZ

Slope 12 % Wide / Narrow 1 % Wide / Narrow

Soil Erodible Wide / NarrowNot erodible Wide / Narrow

Plants Dense Wide / NarrowSparse Wide / Narrow

Common sense guidelines on width of buffer strip needed to be effective.

Cover crops

Reduce runoff and erosion?

Retain N, i.e., reduce NO3- leaching?

Add organic matter?

If a legume, is less N fertilizer needed?

These provide better cover of the soil than just what-ever weeds emerge. Thus, there is less effect of rain-drop impact on soil detachment and slower runoffvelocity means more time for infiltration. Since thecrop uptakes soluble N (e.g., NO3

-), there is lessleaching and if a legume, there is net input of N intothe soil so less need for subsequent fertilization.

Planted cover crops produce morebiomass than native weeds so addmore organic matter.

Vetch

Dead vetch

Conservation tillage

> 30 % of soil surface with residue

Reduces / increases runoff and erosion?

Reduce. This is a matter of coverage of the soil. The more, the betterwith respect to runoff and erosion.

Conservation tillage?

Crop rotations

Help minimize inputs

Break weed, disease and insect cycles

Simulate beneficial microbes

This study indicated thatincreasing the time spentin legume both increasedcorn yields and diminishedthe benefit / need for Nfertilization.

The treatments werecontinuous corn, C-C-C,rotation with soybeans, anda longer term rotation involving meadow, presumably with clover orgrass-clover mix.

Fertilizers

Organic

Inorganic / synthetic

There are, you know, organic fertilizers thatare chemically synthesized.

Organic Nutrient Sources

Rate based on N requirement of crop

Adds relatively high amount of P

Common problem is that P / N ratio is larger than the crop needs solong-term use of such fertilizer materials leads to build-up of P in thesoil and, therefore, increased potential for P loss to downstreamwater bodies and their eutrophication.

Most N is / is not readily available?

No need to account for slow release of N inestimating future application rate(True / False).

Composition precisely known / variable?

Types

Industrial and Municipal Wastes

Many industrial wastes unfit for land-application due to chemical content

Manure

Disposal problem for feeding operations

A lot of the stuff but not much acreagefor its beneficial use as a fertilizer.

Garbage

Remove glass and metal then compost Municipal solid waste (MSW)

Low nutrient content

Forest products

Sawdust, bark and so forthHigh C / N

Sewage sludge

Dried and used as slow release fertilizerCompostedApplied as slurry or WET CAKE

Inorganic / Synthetic Fertilizers

Various carriers for each nutrient

Grade (N-P-K)

% N - % P2O5 - % K2O

Limiting Factor

von Liebig

Production is no greater than that level setby the growth factor that is present inlowest amount relative to the optimumamount of that factor (limiting factor)

So funky barrel to left is P-limited. Fix that and wind up with funky N-limited barrel.

Questions

Which nutrient to add to soilHow much to addWhat carrier to useHow to apply itWhen to apply it

Soil testing and plant analysis address the firsttwo nutrient management questions. To someextent also the third –when you need more than onenutrient and two can be applied in the same carrier.

Field observations aid interpretation ofplant and soil analyses

Deficiency symptoms

Measure growth and yieldIndicator of fertility status

Plant Analysis

Relationship between concentration ofelements in plant tissue and growth

Deficiency symptoms if very low

Hidden hunger if reduced growth withoutdeficiency symptoms

Critical concentration cutoff for optimalgrowth

Sufficiency

Toxicity

Soil Analysis

Soil sampling

Steps to account for variability

Divide into homogeneous areasSeveral random samplesAvoid atypical areas

Lab analyses

Recommendations based on soil test levelscalibrated to field tests

Best to use lab in State for appropriateprocedures and recommendations

Let’s say there exists a yield curve for crop Y asa function of the level of nutrient X in the soil.Typically, it increases from the origin and levels offwith increasing concentration of X in the soil. Thus,there is an evident concentration of X associatedwith near max yield. Do a soil test and find the concentration of X in your soil is (optimum – yoursoil) low, so add the difference. Concept of calibration.

A lab in NY follows exacting QA / QC and gives excellent analytical results. Itwill also give you, a La. farmer, recommendations based on the soil nutrientextraction protocol it uses and calibration curves for soil and environmentalconditions in NY. Perhaps extraction protocol and calibration curves are notcorrect for La. soils and environment. Make sense?

Recommendations by crop and soil

Greater probability of profitable response if fertility low

Application Methods

Broadcast

Spread evenly

Raise fertility uniformlyPastures and small grains

Situations for which broadcast is appropriate.

Localized placement

Banded or point application

High concentration near part of roots Reduces fixation

Plants get what they need. Excess fertilizer avoided. If fertilizer elementis subject to fixation, concentrated mass of fertilizer in small volume of soilsaturates the fixation capacity of the soil there so much of the applied fertilizer remains soluble and available for plant uptake.

Foliar

Absorption of nutrients through leaves

Adequate for micronutrients

Economic Considerations

N usually most important

P and K added to balance and supplement

N recommendations based on fieldresponse data for different soils overseveral yearsThis is the current situation in La. and many other states –no soil test forN that serves as the basis for recommendations. Rather, the recommendationis based on field plot experiments that indicate the optimum rate on a cropby soil type basis. The reason for no soil test (like total N, nitrate, etc.) is thecomplexity of the N cycle. Recall?

Response versus cost

Maximum economic return is at less thanmaximum yield