COVER CROP PLANT AVAILABLE NITROGEN (PAN) CALCULATOR KOON-HUI WANG, ARCHANA PANT, THEODORE RADOVICH, JARI SUGANO, JENSEN UYEDA

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1 COVER CROP PLANT AVAILABLE NITROGEN (PAN) CALCULATOR KOON-HUI WANG, ARCHANA PANT, THEODORE RADOVICH, JARI SUGANO, JENSEN UYEDA Center of Rural Agricultural Training & Entrepreneurship

2 Cover cropping Cover the soil at all time Reduce soil disturbance Grow a living root 24/7 Synergize with diversity: Crop rotation

3 BENEFITS OF COVER CROPPING 1. Reduce fertilizer costs 2. Add organic matter 3. Improve yields by enhancing soil health 4. Reduce the need for herbicides and other pesticides (nematicide) 5. Prevent soil erosion 6. Conserve soil moisture 7. Protect water quality 8. Help safeguard personal health 9. Some cover crops offer harvest possibilities as forage, grazing or seed in multiple crop enterprises.

4 SUMMER LEGUMES, TROPICAL LEGUMES, LOW ELEVATION LEGUMES Leguminous cover crops can contribute significant amount of nitrogen to crop production. However, farmers need a better tool to accurately estimate the nitrogen contribution from legumes so as to precisely reduce fertilizer rates. Sunn hemp Cowpea Lablab Pigeon pea Velvet bean

5 WINTER LEGUMES COOL SEASON LEGUMES, HIGH ELEVATION LEGUMES Woolypod vetch Hairy vetch Bell bean Austria winter pea White clover

6 NON-LEGUMES Annual ryegrass Oat TAMU 406 Sorghum-sudangrass Oil radish SodBuster

7 Grass High Elevation Broad Leaves Low Elevation Grass Legume Nematode Resistant

8 PLANT AVAILABLE NITROGEN (PAN) Although cover crops can fix or accumulate nitrogen (N) in plant tissues, not all the N in the tissue will be released into a plant available form. At 28 days after cover crop incorporation At 70 days after cover crop incorporation [NO 3- ] [NO 3- ] Plant Available Nitrogen (PAN %) = [Soil nitrate with cover crop (mg/kg) - soil nitrate without cover crop] X 100 Total N added by cover crop (mg/kg) % N in tissue cover crop biomass Total = N

9 FACTORS AFFECTING PAN% FROM COVER CROP climate conditions, season soil types cover crop species biomass, plant age, % N in tissue time after cover crop termination farming practice (till vs no-till) microbial activities in your soil

10 PAN FROM COVER CROPS IN POAMOHO, OAHU (WINTER) Season/tillage Cover Cropping Practice Cover Crop Tissue 28 Days 70 Days Cover Crop Fresh Weight (lb/ft 2 ) Dry Content (%) Dry Weight (lb/acre) Tissue N (%) Total N(lb/A) PAN (%) Actual PAN (lb/a) PAN (%)2 Actual PAN(lb/A) Winter/Till Sunn hemp % Winter/Till Cowpea (Blackeye #5) % Winter/Till Lablab % Winter/Till Pigeon pea % Winter/Till Woolypod vetch % % Tissue N varied among cover crop species. Total N from cover crop is based on biomass % tissue N. Some cover crop released PAN more efficiently than others (70.5% vs 55.2%). Actual PAN can be strongly influenced by cover crop biomass.

11 CONVENTIONAL TILL vs NO-TILL Till No- Till

12 PAN FROM COVER CROPS IN POAMOHO, OAHU (WINTER) Season/tillage Cover Cropping Practice Cover Crop Tissue 28 Days 70 Days Cover Crop Fresh Weight (lb/ft 2 ) Dry Content (%) Dry Weight (lb/acre) Tissue N (%) Total N(lb/A) PAN (%) Actual PAN (lb/a) PAN (%)2 Actual PAN(lb/A) Winter/Till Sunn hemp % Winter/Till Cowpea (Blackeye #5) % Winter/Till Lablab % Winter/Till Pigeon pea % Winter/Till Woolypod vetch % Winter/No-till Sunn hemp % Winter/No-till Cowpea (Blackeye #5) % Winter/No-till Lablab % Winter/No-till Pigeon pea % Winter/No-till Woolypod vetch % PAN % released was slightly reduced in no-till compared to tilled plots except for sunn hemp.

13 PAN FROM COVER CROPS IN POAMOHO, OAHU (SUMMER) Season/tillage Cover Cropping Practice Cover Crop Tissue 28 Days 70 Days Cover Crop Fresh Weight (lb/ft 2 ) Dry Content (%) Dry Weight (lb/acre) Tissue N (%) Total N(lb/A) PAN (%) Actual PAN (lb/a) PAN (%)2 Actual PAN(lb/A) Winter/No-till Sunn hemp % Winter/No-till Cowpea (Blackeye #5) % Summer Summer/No-till Sunn hemp % Summer/No-till Cowpea % Summer/No-till Lablab % Summer/No-till Sudex % Summer/No-till Oat (TAM406) % Summer/No-till Oil Radish % PAN released % was higher in summer than winter. Grassy cover crops had lower % N and slower PAN released % compared to legumes, but that in oil radish was equivalent or higher than legumes.

14 PAN FROM COVER CROPS IN LALAMILO, HAWAII Season/tillage Cover Cropping Practice Cover Crop Tissue 28 Days 70 Days Cover Crop Fresh Weight (lb/ft 2 ) Dry Content (%) Dry Weight (lb/acre) Tissue N (%) Total N(lb/A) PAN (%) Actual PAN (lb/a) PAN (%)2 Actual PAN(lb/A) Winter/Till Bell bean % Winter/Till Austrian Winter Pea % Winter/Till Annual ryegrass % Winter/Till Woolypod vetch % Winter/Till Oat (Cayuse) % PAN released % could change from location to location. Although N % in these cover crops were higher than the tropical legumes tested earlier, the actual PAN released were lower. Farmers could calculate amount of N fertilizer Total N requirement for your crop: A = $ (Recommended by ADSC) N available from your cover crop: B = #VALUE! Amount of N you need to fertilize for your crop: A-B =

15 CONCLUSION Although PAN release rates at 70 days after cover crop termination were similar among all legumes and oil radish tested, actual PAN released varied mainly due to the biomass generated. Thus, it is a good practice for farmers to estimate cover crop biomass accumulated prior to termination of cover crop. Graminaceous cover crops generally had lower PAN%, resulted in lower actual PAN regardless of the biomass generated. None-the-less, graminaceous cover crops are good nutrient scavenging crops, and soil C builders. Majority of the PAN was released during the first 28 days after cover crop termination, thus additional fertilizer should be added there after.

16 FUTURE DEVELOPMENT OF COVER CROP CALCULATOR IN HI PAN % PAN% Prediction Curve at Waiamea (A) Y = X R 2 = P< d PAN % PAN% Prediction Curve at Poamoho d PAN R 60 2 = d VK equation Y = X R 2 = 0.54 P< VK equation Tissue N % Tissue N % Generate PAN% prediction curve based on %N in cover crop tissues (any cover crop mix will work) from reginal locat However, Hawaii has so much microclimates and soil types. Plan to correlate soil health indicators with PAN%

17 CHALLENGES OF GROWING COVER CROPS 2015 MEALANI TRIAL

18 WINTER COVER CROPS 2015 MEALANI TRIAL 2.5 months after seeding cover crops Alfalfa Austrian winter pea Seeds planted in Feb 2014 Pisum sativum arvense lb/a 100 Bell bean Vicia faba 200 Hairy vetch Vicia villosa 40 Yellow sweet clover New Zealand White clover Melilotus officinalis 20 Trifolium repens 15 Annual ryegrass Lolium multiflorum 100 All legumes die back Cayuse oat Avena sativa 90

19 SOIL TEST 2015 MEALANI TRIAL Soil was low in P, K, Ca, and Mg, and some time ph

20 WHEN COVER CROP ESTABLISH SLOW, YELLOW NUTSEDGE IS COMPETITIVE Annual ryegrass Bell bean was chlorotic Hairy vetch was purplish White clover and yellow sweet clover hardly grow

21 DISEASES ON WINTER COVER CROPS 2015 MEALANI TRIAL Cayuse oat is susceptible to rust Puccinia coronate (Crown rust) Annual ryegrass mostly grow well except in one corner with very low P, leaves were reddish and plants are stunted Surprisingly, oat was growing very well initially.

22 SUMMER COVER CROPS Soil was amended with lime, superphosphate, and minute of potash. All legumes were inoculated with rhizobium. 3 months after seeding cover crops Cowpea Seeds planted in May 2014 Vigna unguiculata Seeds (lb/a) 120 Lablab Lablab purpurea 100 Pigeon pea Cajanus cajan 75 Soybean Glycine max 75 Sunn hemp Crotalaria juncea 60 Velvet bean Mucuna pruriens 40 Sodbuster oil radish Raphanus sativus 10

23 COVER CROPS WITH POOR ESTABLISHMENT (1 month after planting) Poorest Intermediate Poor Excellent Sunn hemp Pigeon pea cowpea Soybean (senence early) Velvet bean lablab

24 COVER CROP WITH EXCELLENT ESTABLISHMENT (1 month after planting) Excellent Annual ryegrass Black oat Oil radish

25 BIOMASS Mealani Trial (3 months after planting)

26 DISEASES ON SUMMER LEGUMES 2015 MEALANI TRIAL Angular leaf spot (Phaeoisariopsis griseola) on most legumes when young Cylindrocladium/Calonectria on soybean after heavy rain lablab Sunn hemp 0.aspx

27 Marla Fergerstrom and Farm Crew from Mealani Station Randy Hamasaki, Brian Bush Maria Derval Diaz Donna Meyer, Gareth Nagai, Shelby Ching, Shova Mishra, Sarah Moore Roxana Myers, Cathy Mello, Justin Bisel oads/crate_ccpancalculatorposter.pdf oads/p-high-elevation-covercrops.pdf oads/ccchart-hawaii-khwang.pdf /articles/v19-pant-coolseasoncc.pdf ACKNOWLEDGEMEN T This project is supported in part by NRCS CIG grant (project number 69-3A ) and in part by NIFA CRATE program (project number ). Reference links

28 FARMER S SAMPLES 28 day PAN (%) 28 day Actual PAN (lb/a) 40 day PAN (%) 40 day Actual PAN (lb/a) Dry wt (tons/a) Tissue N (%) Hirayama Bonk Robbs Hirayama Bonk Cover crops vetch, red clover, spring pea, oats Oil radish, vetch Cayuse oat, bell beans, purple vetch, Austrian winter