Cover Crop Rotations in Vegetable Production Systems Danielle Treadwell, Horticultural Sciences, University of Florida and Stuart Weiss, Agronomy, University of the Virgin Islands Outline 1. Key resources about cover crops and crop rotations, 2. Criteria for cover crop species selection, 3. Best seasonal opportunities to integrate covers in vegetable systems, and 4. Methods to optimize benefits through innovative planting and termination. Sunn hemp in bloom at 83 Farms in Bell, Florida. Key Cover Crop Resources • USDA-ARS and Land grant university faculty and extension specialists • eXtension • You Tube • SARE • NCAT/ATTRA Key Cover Crop Resources • USDA-ARS and Land grant university faculty and extension specialists • eXtension • You Tube • SARE • NCAT/ATTRA Key Cover Crop Resources • USDA-ARS and Land grant university faculty and extension specialists • eXtension • You Tube • SARE • NCAT/ATTRA Key Cover Crop Resources • USDA-ARS and Land grant university faculty and extension specialists • eXtension • You Tube • SARE/NCAT/ATTRA • Rodale Institute http://www.sare.org/publications/croprotation /croprotation.pdf Key Cover Crop Resources • USDA-ARS and Land grant university faculty and extension specialists • eXtension • You Tube • SARE, NCAT/ATTRA • Rodale Institute http://www.rodaleinstitute.org/no-till_revolution Criteria for Cover Crop Species Selection • Consider the pathogen and insect spectrum important for income-producing crop • Select cover crop species from different plant families as the income crop to interrupt life cycles and reduce pest populations • Most of the cover crops currently in use in commercial production systems are not named varieties Crop Planning: Cultivar Selection and the Importance of Named Cultivars • FL producers import seed • Most seed is labeled “Common” or “VNS” – Sunn hemp (Crotalaria juncea L.) ‘Tropic Sun’ developed by the University of HI and ‘Auburn Gold’ developed by Auburn University – Other sunn hemp is shipped from India and Africa – Small grains from NC and the midwest – Other tropicals grown in Brazil, Mexico, Thailand, & Africa VNS Crotalaria juncea from Africa Cover Crop Species & Nematodes Gevens et al., unpublished data Cowpea Cultivars & Nematodes Gallaher and McSorley, 1993 Monocultures Neighbor's land use, previous and subsequent crop families very important. Plant architecture and carbon form and content will influence termination method. Polyculture (mixed) Species Polycultures reduce the period of time needed for soil biota to return to equilibrium but may differ in maturity rates, complicating termination plans. Root Distribution in the Soil • Cover crop roots take some time to develop. • Winter annuals tend to invest more plant energy in root production than summer annuals early on. • Consider mixing species with different root architecture. Increased Direct and Seasonal Costs Modify Existing Equipment Great Plains 3P605 NT Drill with raised drive wheels Florida Vegetable Rotations St. Johns/Flagler County: Winter cabbage  Spring potato  Summer cover crop sorghum Suwannee County: Winter cover crop rye  Spring watermelon  Summer greens  OR Winter cover crop rye  Spring tomato  Summer fallow  Fall cucurbit Collier County: Winter strawberry  Spring water/muskmelon  Summer cover crop sorghum South to Tropics Leveraging Seasonal Changes 1. For most of the southeastern U.S., winter is a good fit for cover crops (temperature) 2. Summer and Winter are both possible in Gulf States (temperature and rainfall) 3. Cover crops can be produced year-round in subtropics/tropics, but best during summer (rainfall) Fall mustard mix following summer sorghum Sudangrass and preceding winter potato in St. John’s County FL Vegetable Transplants or Seeds? • Larger transplants and seeds establish more readily in surface sheet mulch systems than smaller ones • Small seeds and small transplants may be slow to establish (or perish) • if planted during the Green Bridge or • if planted in heavy residue. How Do I Begin the Process of Cover Crop Integration? 1. Identify major constraints to profit, and select covers and management practices that will reduce external costs in the short or long term 2. Identify current resources and equipment 3. Narrow species options by ruling out those that require more or less time to develop than your current rotational plan allows 4. Eliminate species and cultivars that are alternate hosts to pests 5. Select species that attract beneficials 6. Leverage seasonal temperature and precipitation changes to manage covers and reduce labor/fuel costs Methods to Optimize Benefits of Cover Crop Integration 1. In-situ 2. Cut and Carry 3. Green Manure 4. Roller-Crimp 1. Cover Crop In-situ Benefits and Risks • Trap /retain nutrient - enriched sediments and particulates • Improve water infiltration and nutrient adsorption • Extend growing season to use available nutrients • Reduce in-field volume of runoff water (Dinnes, 2004) • A poor cover stand encourages weed establishment • Alternative host for pests Cover Crops Retain N in the Soil J. Luna, OSU, Corvallis 2. Cut and Carry Best Practices • Producing biomass, harvesting straw for another location, and keeping stubble residue in place serves a dual purpose. • Be mindful of the risk of contamination from weed seeds or pathogens. Herbicide residues may also be a concern. • 4 tons/acre dry matter is the commonly accepted threshold for weed suppressive benefits, but more may be needed to suppress large seeded weeds or perennial weeds. 2. Vegetable Management following Cut and Carry • In early spring, delay application of straw until after transplants/seeds have established root system if soil temperatures are less than optimal, or soil moisture is limiting • Apply dry granular fertilizer and incorporate into soil via BMP recommendations prior to applying straw • If drip tape is used, apply before straw • Fewer pests with cut and carry than green surface sheet mulch initially (mammals, birds, cutworms) 3. Cover Crop Mowing Best Practices • Flail mowers (ex. Befco, Alamo) use blades and deposit residue under deck (safety) in uniformly sized pieces. Can be offset, good for uneven terrain if outfitted with a gauge roller. • Rotary mowers (ex. Bush Hog) use chains, deck size larger, throws mulch outside of deck, uneven pieces. 3. Vegetable Management following Mowing, with Residue on the Surface • Mechanical transplanting may be difficult • Direct seed with drill possible with no-till drill • Small seeded vegetables direct seeded into soil may exhibit poor germination due to allelopathic chemicals from cover crops • Increased predation of seeds, transplants from mammals and birds 3. Green Manure/Full Incorporation Best Practices • Heavy residue may require multiple passes with disk to fully incorporate. • A 2-6 week period is recommended to allow soil biota to return to equilibrium (Green Bridge). Time period is reduced as temperatures increase and soil moisture is optimal. • Nitrate leaching is possible during the Green Bridge, so timing is critical. Goal: Synchronize N with Crop Demand Gaskell et al., 2006 4. Surface Sheet Mulch – Rolling/Crimping • Best practices following successful rolling/crimping • Large-seeded, larger transplants establish more readily • Spacing – canopy closure and drip emitter spacing • Regrowth Brock Family Farms, Monticello, FL 4. Vegetable Management following Roller-Crimping • Mechanical transplanting follows direction of rolling • Direct seed with drill possible with no-till drill • Consider banding dry granular organic or conventional fertilizer • Small seeded vegetables direct seeded into soil may exhibit poor germination due to allelopathic chemicals from cover crops • Young transplants may survive early frost in fall, and have access to increased soil moisture due to reduced evapotranspiration rates Managing Summer Cover Crop to Vegetable Crop Rotations in Hot Humid Environments • Farm management may need to be different in summers compared to the other seasons. • Differences in seasonal decomposition rates, precipitation, temperature, microbial activity, solar radiation, nutrient volatilization (to name a few) impact cover crop management choices. • Full tillage vs. conservation tillage choices Conventional Full Tillage Crop Rotations Sorghum Sudan – SS Pearl Millet – PM Velvet Bean – VB Sunn Hemp - SH Cycle 1 Cycle 2 Cycle 3 Rotation Fall (Rainy) Spring (Dry) Summer (Dry) 1 SS tatsoi sweet corn 2 PM tomato cucumber 1 SS tomato cucumber 2 PM tatsoi sweet corn 1 VB tatsoi sweet corn 2 SH tomato cucumber 1 VB tomato cucumber 2 SH tatsoi sweet corn Grass Cover Crops - Monocultures Sorghum-sudan var. Mega Green Pearl millet var. Mega Mill Legume Cover Crop and Grass/Legume Mixtures Sunn hemp Sunn hemp and Pearl Millet Soil organic matter percent in the top 20 cm of soil following cover crop termination but prior to incorporation Organic matter (%) by cover crop rotation CC Year 1 CC Year2 Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5 Cycle 6 WF 4.9ab 4.9 3.4ab WF 3.5 2.7b 2.3 SS 5.5a 5.7 3.1b PM 3.3 2.5b 2.2 PM 4.4ab 5.4 3.9ab SS 3.5 3.1ab 2.6 VB 3.7b 6.7 3.9ab SH 3.7 3.4a 2.7 SH 4.5ab 5.9 3.8ab VB 3.7 2.9ab 2.6 SSVB 5.3ab 5.6 3.6ab SHPM 3.7 3ab 2.5 SHPM 4.5ab 5.5 4.1a SSVB 3.4 2.9ab 2.6 Soil nitrate concentration in the top 20 cm of soil following cover crop termination but prior to incorporation NO3-N (ppm) levels by cover crop rotation CC Year 1 CC Year 2 Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5 Cycle 6 WF 71 58 29 WF 30 36 25b SS 90 63 38 PM 30 44 28ab PM 91 57 38 SS 27 44 27ab VB 86 56 42 SH 34 31 32a SH 88 54 46 VB 31 24 28ab SSVB 92 69 35 SHPM 40 38 27ab SHPM 84 64 34 SSVB 29 33 28ab Implications • In hot humid tropical environments cover crops may have little to no effect to improve or maintain soil fertility in intensive organic vegetable crop systems utilizing conventional tillage in low-external-input farming systems. • Cover crops contribute many sustainable ecosystem benefits and thus need to be incorporated into a holistic management plan. Cover Crop Residue Surface Sheet Mulch – Increases soil conservation through reduced tillage – Decomposition of CC sheet residue allows for the slow release and conversion of organic matter to plant available nutrients – Sheet residue more efficiently converts carbon into soil organic matter – Sheet residue acts as a barrier against weeds – Surface plant residues provides a beneficial microorganism rhizosphere – Allows for planting of the vegetable rotation shortly after termination when the crop residue dries. (Southern SARE, 2012, Sullivan, 2011; Curran and Ryan, 2010, Hoorman et al., 2009; Wang and Klassen, 2005; Sullivan, 2003; NRCS, 2002) Sunn Hemp Sorghum Sudan Lab Lab Replicate Cover Crop Performance and Nitrogen Contribution from Vegetative Biomass at Termination No difference was observed in CC plant tissue phosphorus or potassium levels Measuring Results After Roll Down Termination • Cover crop residue height and re-growth was assessed at 28 and 42 days post roll down to determine the effectiveness of roller-crimper technology on cover crops in the tropics • Weed biomass was measured at 28 and 42 days post roll down to determine the impact of the resulting surface sheet mulch to inhibit weed development. 28 days post roll down Cover Crop Establishment • Germination 7 DAP and drip tape placement Pigeon Pea 47 DAP Sun Flower 47 DAP Weedy Fallow Control Sunn Hemp 47 DAP Sampling Procedures Prior to Termination • Biomass sampling of cover crops and volunteer weeds – 3 random 0.25m2 samples collected per plot prior to CC kill – CCs and weeds were separated – Weeds were sorted by class (grass and broad leaf) – Samples were dried in a forced air oven to determine dry matter Cover Crops at Maturity Prior to Termination (112 DAP) Cover Crop Performance. Weed Development, and Nitrogen Contribution from at Termination No difference was observed in CC plant tissue phosphorus or potassium levels Treatment Plant Biomass at CC Termination kg/ha-1 Total kg/ha-1 Control NA NA NA Control BL 862 ± 293a Control GW 1,429 ± 293ac Pigeon Pea PP 4,747 ± 293b 4,747 ± 336b Pigeon Pea BL 273 ± 293ad Pigeon Pea GW 393 ± 293ad Sun Flower SF 2,027 ± 293ac 2,027 ± 336a Sun Flower BL 180 ± 293d Sun Flower GW <1 ± 293d Sunn Hemp SH 6,418 ± 293e 6,418 ± 336d Sunn Hemp BL <1 ± 293d Sunn Hemp GW <1 ± 293d Cover crop (CC), broad leaf (BL) weed, and poacea (GW) weed biomass (kg/ha-1) within treatments assessed at cover crop termination (112 DAP) 2,291 ± 336a 667 ± 336c 180 ± 336c <1 ± 336c Values within the same column group followed by different letters differ (p<0.05) according to a least significant range seperation. 92 65 33 0 10 20 30 40 50 60 70 80 90 100 Sunn Hemp Pigeon Pea Sun Flower kg/ha-1 Estimated Nitrogen Contribution from Cover Crop Biomass at Termination (112 DAP) Estimated Nitrogen Contribution Different letters indicate a significant difference (p<0.05) a b c Custom Built Roller-Crimper • Cover crops were terminated at 112 DAP with a custom built roller-crimper – Built from a recycled 24 inch disc plough using the disc and plough hubs, 24 inch steel pipe, steel tubing, and steel flat bar. Cover Crop Termination with Roller-Crimper and Crop Residue Surface Sheet Mulch Pigeon Pea Sunn Hemp Sun Flower Control Jalapeno peppers (Invicto-F1) grown in a green house and transplanted into treatment plots 42 DAP and 7 days after CC termination Control Sun Flower Pigeon Pea Sunn Hemp Cover Crop Re-Growth and Weed Development at 3 and 6 weeks after CC Termination 1.) At 3 weeks after CC termination, SH surface residue provided the greatest reduction in weed development. 2.) Sun flower was effectively killed with a roller- crimper showing no regrowth. 3.) At 6 weeks after CC termination, SH continued to reduce weed development with less GW than all other treatments and less BL weeds than PP or SH, but similar to the control. SH regrowth increased. Treatment CC BL GW Control NA 27 ± 80a 47 ± 80a Pigeon Pea 307 ± 80b 416 ± 80b 93 ± 80a Sun Flower 0 ± 80a 440 ± 80b 451 ± 80b Sunn Hemp 144 ± 80b 13 ± 80a 0 ± 80a Treatment CC BL GW Control NA 378 ± 328a 591 ± 238a Pigeon Pea 1,413 ± 328b 1,676 ± 328b 282 ± 238ac Sun Flower 0 ± 328a 1,691 ± 328b 782 ± 238ab Sunn Hemp 2,229 ± 328b 409 ± 328a 20 ± 238c Cover crop (CC), broad leaf (BL) weed, and poacea (GW) weed biomass (kg/ha-1) by treatment at 3 and 6 weeks after cover crop termination 3 Week Harvest 6 Week Harvest Values within the same column group followed by different letters differ (p<0.05) according to a least significant range seperation. Sunn Hemp Sun Flower Pigeon Pea Control Sunn Hemp Control Pigeon Pea Sun Flower Cover Crop Re-Growth and Weed Development at 9, 12, and 15 weeks after CC Termination Low frequency weeding at 6, 9, and 12 weeks reduced SH and PP regrowth to minimal levels, however, SH and PP regrowth in non-weeded plots became major weeds. In weeded plots, CCs minimized weed development similar to conventional tillage through week 12. Sunn Hemp Sunn Hemp Control Control Pigeon Pea Pigeon Pea Sun Flower Sun Flower Treatment CC BL Grass Control NA 69 ± 52a 167 ± 52ab Pigeon Pea 71 ± 52a 253 ± 52b 204 ± 52a Sun Flower 0 ± 52a 51 ± 52a 98 ± 52ab Sunn Hemp 64 ± 52a 207 ± 52b 40 ± 52bc Treatment CC BL Grass Control NA 67 ± 44a 220 ± 44ab Pigeon Pea 0 ± 44a 196 ± 44b 160 ± 44ab Sun Flower 0 ± 44a 109 ± 44ab 127 ± 44a Sunn Hemp 20 ± 44a 153 ± 44ab 247 ± 44b Treatment CC BL Grass Control NA 896 ± 289ab 1,251 ± 289a Pigeon Pea 53 ± 289a 1,471 ± 289b 1,444± 289a Sun Flower 0 ± 289a 616 ± 289a 1,498 ± 289a Sunn Hemp 0 ± 289a 1,409 ± 289b 2,409 ± 289b 15 Week Harvest Cover crop (CC), broad leaf (BL) weed, and poacea (GW) weed biomass (kg/ha-1) from WEEDED sub-plots by treatment at 9, 12, and 15 weeks after CC termination Values within the same column group followed by different letters differ (p<0.05) according to a least significant range seperation. Sub-plots weeded at 6, 9, &12 weeks. 9 Week Harvest 12 Week Harvest Treatment CC BL Grass Control NA 1,018 ± 457a 2,138 ± 457b Pigeon Pea 2,904 ± 457c 1,471 ± 457a 422 ± 457a Sun Flower 0 ± 457a 1,962 ± 457a 1,880 ± 457b Sunn Hemp 1,027 ± 457b 820 ± 457a 207 ± 457a Treatment CC BL Grass Control NA 1,282 ± 560a 3,256 ± 560a Pigeon Pea 3,387 ± 560a 1,807 ± 560a 793 ± 560b Sun Flower 0 ± 560b 1,856 ± 560a 2,344 ± 560a Sunn Hemp 3,147 ± 560b 1,873 ± 560a 147 ± 560b Treatment CC BL Grass Control NA 1,031 ± 629a 4,844 ± 629c Pigeon Pea 3,849± 629a 451 ± 629a 1,651 ± 629a Sun Flower 0 ± 629b 1,204 ± 629a 3,396 ± 629bc Sunn Hemp 1,193 ± 629b 2,113 ± 629a 1,738 ± 629ab Cover crop (CC), broad leaf (BL) weed, and poacea (GW) weed biomass (kg/ha-1) from NON- WEEDED sub-plots by treatment at 9, 12, and 15 weeks after CC termination 9 Week Harvest 12 Week Harvest 15 Week Harvest Values within the same column group followed by different letters differ (p<0.05) according to a least significant range seperation. Vegetable Management following Rolling/Crimping • Select the correct cover crop to vegetable crop pairing. • Cover crops that produce large amounts of biomass resulting in coarse, thick matted surface mulch can be paired with long rotation vegetables (70 to 120 days to harvest) • These transplants should be larger and more mature than when transplanted into fully tilled beds. • Cover crops that result in less biomass, produce surface mulch that has a rapid decomposition rate, or is finer in nature can be paired with short rotation vegetables (30 to 60 days to harvest) and may be transplanted or direct seeded. Jalapeno Pepper Harvest First pepper harvest occurred on April 8, 2013 (112 DAP or 70 DAT). Peppers where harvested from data rows, graded (marketable or unmarketable), and weighed. There were a total of 9 pepper harvests with the final harvest on June 21, 2013. Jalapeno Pepper Plant Development at 1st Harvest (112 DAP) in Weeded Sub-Plots Sun Flower Control Pigeon Pea Sunn Hemp Jalapeno Pepper Production • Low frequency weeding of Sunn Hemp plots resulted in the greatest pepper yield, most fruit per plant, and the heaviest fruit. • Non-weeded plots followed similar trends, but with severely reduced yields , fruit per plant, and individual fruit weight. Treatment Marketable Unmarketable Sunn Hemp 8,567 ± 1,325a 151 ± 45a Control 6,060 ± 1,325ab 84 ± 45a Sun Flower 2,697 ± 1,325b 38 ± 45a Pigeon Pea 2,214 ± 1,325b 69 ± 45a Treatment Marketable Unmarketable Sunn Hemp 3,468 ± 754a 99 ± 25a Control 1,312 ± 754ab 35 ± 25ab Sun Flower 617 ± 754b 9 ± 25a Pigeon Pea 155 ± 754b 5 ± 25a Non-Weeded Pepper Yield Values within the same column group followed by different letters differ (p<0.05) according to a least significant range seperation. Sub-plots weeded at 6, 9, &12 weeks. Jalapeno pepper yields (kg/ha-1) from weeded and non-weeded sub-plots by treatment Weeded Pepper Yield Treatment Weeded Non-Weeded Sunn Hemp 17 ± 3a 6.1 ± 1a Control 13 ± 3ab 2.3 ± 1ab Sun Flower 6 ± 3b 0.3 ± 1b Pigeon Pea 5 ± 3b 1.1 ± 1b Treatment Weeded Non-Weeded Sunn Hemp 15.1 ± 1a 16 ± 3a Control 14.5 ± 1ab 17 ± 3a Sun Flower 12.7 ± 1b 10 ± 3a Pigeon Pea 12.7 ± 1b 18 ± 3a Mean Marketable Fruit Wt. (g) Values within the same column group followed by different letters differ (p<0.05) according to a least significant range seperation. Sub-plots weeded at 6, 9, &12 weeks. Mean marketable jalapeno pepper fruit per plant and individual fruit weight (g) from weeded and non-weeded sub- plots by treatment Mean Marketable Fruit/Plant Implications and Summary Cover crops can be a valuable management tool in the tropics that require few if any external inputs. Cover crop re-growth may cause weed problems when using a roller-crimper for termination of specific CC species in tropical or extended warm season environments. For indeterminate cover crops, roller-crimper termination may not be viable without additional management. Surface sheet mulch resulting from CCs terminated with a roller-crimper can be used for natural weed suppression and to protect soil quality for subsequent crop rotations. Summary • We have made a lot of progress on refining these systems, but they are not without risk - be prepared to have a back up plan to manage undesirable cover crop results. • Design an approach that is fully supported by the equipment on hand. • Recommended vegetable cultivars, planting practices and fertilization strategies apply for conventional practices and not necessarily high residue cc systems. We still have a lot to learn, but we will get there together… Acknowledgements