Enhancing Soil Fertility with Cover Crops. Mike Daniels Professor, Extension Water Quality and Nutrient Management

Transcription

1 Enhancing Soil Fertility with Cover Crops Mike Daniels Professor, Extension Water Quality and Nutrient Management

2 Outline Definitions and Basics How Cover Crops enhance Soil Fertility Cover Crops and Water Quality

3 Cover Crop Crops grown to provide ground cover to reduce soil erosion and nutrient losses Green Manure - Crops grown to add or retain nutrients in the soil and usually incorporated Cover crops are usually divided into legumes (Fix nitrogen from the atmosphere) and nutrient scavengers (grasses, mustards, tillage radish, etc.)

4 Advantages Reduce soil erosion Increase residue cover Increase water infiltration Increase soil organic matter Improve soil physical properties Recycle nutrients Weed control Increase beneficial insects Increase microbial activity Potential forage harvest Disadvantages Must be planted when time is limited Additional costs (planting and killing) Reduce soil moisture May increase pest populations May increase risks of diseases Difficult to incorporate with tillage Allelopathy *Dabney et al., 2001

5 Increasing Soil Organic Matter (Long Term) Manipulating Nutrient Cycling To Our Benefit Promoting N fixation with Legumes Catching NO 3- -N before leaches Uptaking nutrients from deep soil layers and placing back into cycle

6 Increases soil ability to store nutrients and water Residual nutrients reside in Organic Matter Increases Cation Exchange Capacity and holds K. Ca, Mg, Fe, Zn, Cu, Mn and Mg Provides carbon for microbial activity that converts organic forms of nutrients to plant-available forms

7 Increases Water Holding Capacity in sandy soils Increases percolation in clayey soils Improves soil aggregation and structure Improves soil tilth

8 Organic matter is complex but can generally be broken down to the active fraction and the stable fraction Active Fraction - Highly reactive and decomposes quickly Stabile Fraction decomposes slowly

9 Responsible for the Release of most N and some of P and K Decomposes rapidly and completely Doesn t contribute to building of organic matter

10 Also known as humus Gives the dark look and spongy feel Increases water holding capacity and infiltration Increases Cation Exchange Capacity

11 Conventional Tillage slow Organic Matter Build up Incorporates plant residue into soil Exposes more surface area for microbes and oxygen Reduces the size of organic residue thereby increasing surface area

12 Conservation Tillage quickens Organic Matter Build up plant residue left on soil Larger residue has less surface area

13 Increasing Soil Organic Matter (Long Term) Manipulating Nutrient Cycling To Our Benefit Promoting N fixation with Legumes Catching NO 3- -N before leaches Recycling nutrients from deep soil layers

14

15 Innoculate seed with symbiotic bacteria Ensure adequate soil fertility as N-fixation requires Mo, Fe, K, S, and Zn Avoid water logged and compacted soils Soil ph > 5.0 and optimum between 6 and 7

16 Purpose: To add N to the system through fixation of N from Atmosphere Legumes do not pump N directly into soil but uptake N and store in plant in organic form N enters soil from decomposition of plant Use as green manure may release much of the N in first 7 to 30 days Kill legumes no later than mid-flowering

17 Plant species Fertility Level Precipitation Length of growing season Soil

18 Increasing Soil Organic Matter (Long Term) Manipulating Nutrient Cycling To Our Benefit Promoting N fixation with Legumes Catching NO 3- -N before it leaches Recycling nutrients from deep soil layers

19 Use grasses and grains instead of legumes Use after lower yield years to soak up excess Nitrate Promote Biomass Production in fall and winter Promote Deep Rooting plants to better recovery For Compacted soils, use biological plowing with plants such as tillage radishes Follow recommendations for Establishment

20 Depends on: Biomass production and nutrient uptake Decomposition rates Amount of N released is difficult to predict without knowing biomass production and decomposition rate

21 Nutrient Uptake by Cover Crops Crop Biomass* Nitrogen Potassium Phosphorus Magnesium Calcium lbs/ac lbs/ac lbs/ac lbs/ac lbs/ac lbs/ac Hairy Vetch 3, Crimson clover 4, Austrian W. P. 4, Rye 5, *Dry weight of aboveground plant material.

22 N replacement Values for Subsequent Cash Crop N replacement Cover Crop value (lbs/acre) Reference Hairy vetch Ebelhar, et al., 1984 (20) Hairy vetch 170 Utomo, et al., 1990 (21) Winter legumes Hargrove, et al.,1986 (22) Hairy vetch 110 McVay, et al., 1989 (23) Crimson clover 88 McVay, et al., 1989 (23) Winter legumes 75 Tyler, et al., 1987 (24)

23 Soil and Air temperature Soil Moisture Amount of N released is difficult to predict without knowing decomposition rate Carbon to Nitrogen Ratio of Organic Substrate (C:N) of 25:1 or less to avoid immobilization

24 Organic Material C:N Ratio Decomposition Rate Remove N from Soil Young rye plants 14:1 Fast No Rye at flowering 20:1 Fast No Hairy vetch 10:1 to 15:1 Fast No Crimson clover 15:1 Fast No Corn stalks 60:1 Slow Yes Sawdust 250:1 Very Slow Yes

25 Legumes decompose faster and leave little Organic Matter Behind and produce larger amounts of N Grains and grasses decompose slower and contribute to stable Organic Mattter and humus and produce less N Fibrous and woody plants decompose slowly and will tie up N for a short period until C:N ratio is lowered Correct by adding starter N Usually short term 1 to three weeks

26 More effective in utilizing N by reducing rapid decomposition by legumes and increasing slower release by grasses/grains If residual soil N levels are high, then grasses will dominate If residual soil N levels are low, legumes will dominate Serves dual purpose of making more N available for next crop while reducing leaching losses

27 Legumes can decompose too rapidly (Within 7 days) releasing N before new crops needs it Conventional tillage and aggressive disking may cause rapid decomposition and relase Prone to denitrification and leaching No-till/ Conservation tillage can slow decomposition and release Leaving residue on surface may promote ammonia volitazation and P losses in runoff - Less likely than denitrification and leaching

28 Keep P in organic form will promote cycling Unless soil saturated with P, it is bound tightly by soil particles Help retain by reducing soil erosion Some legumes host mycorrhizae fungi that are efficient in absorbing P and transferring to plant thereby adding back to Organic Matter when plant decomposes

29 Mngt. Cover Crop Fertilizer N Fertilizer P Runoff Nitrate loss in runoff Total P loss in runoff Lbs.A Lbs./A Inches Lbs/A Lbs/A CT Corn NT - Corn None Rye Grass CT = Conventional Tillage NT = No-Till Sharpley et al., 1991

30 Some Things to Consider Cover cropping provides maximum benefit if practiced for the long term Organic Matter builds very slowly but benefits may be realized before measurable differences occur; goal must be long-term Will be increasing societal pressure to decrease off-farm nutrient losses

31 Thank You