Organic So oil Fertility: General Princciples and New Reseearch Richard Smith Vegetable Crop and Weed Science Farm Advisor University of California Cooperative Extension Monterey County Organic S oil Fertility • We will focus on organic fertility of vegetable crops • We will mostly discuuss nitrogen • Obviously other nutrients are important, especially phosphor us and potassium • Before we spend the time in this discussi on on ni trogen we will br iefl y discuss phosphorus and potassium Soil Phosph horus Levels bicarbonatebicarbonate--exextractable (ppm) Crop Response Response Response likely possible* unlikely Lettuce and <40 40 – 60 > 60 Celery Other cool- < 25 25 – 35 > 35 season vegetables Warm-season < 15 15 - 25 > 25 vegetables * especially in cold soils Soil Potass sium Levels ammonium acetate--extractableextractable (ppm) Crop Response Response Response likely possible unlikely Celery < 150 150 – 200 > 200 Other cool-season < 100 100 – 150 > 150 vegetables Potato, tomato, < 150 150 – 200 > 200 pepper CbitCucurbits < 80 80 – 120 > 120 Phosphorus aand Potassium • Both of these nutriennts can be monitored and managed with the use of soil tests • There are several orgganic sources of these nutrients • High soil pH reducess the availability of bone and rock sources of phosphorus • VVbldiegetable production systems can over time build up high levels of soil phhhosphorus Organic Soil Fertility • Nitrogen is particularly problematic because of various forms it occurs in and transformations it goes through • Mineral nitrogen (nitrate and ammonium) is the plant available form of N in the soil • Large qua nt it ies of N aasoelso exi sts in complex forms in soil organic matter which are not available for ppglant growth • The challenge in organic agriculture is to get sufficient mineraal N from non -mineral N sources Nitrogen Cycle Crop residue, Compost, Soil Organic Matter Most soil N is in this form Fertilizers (1000 ––33000 lbs N/A) Death Mineralization* Death + CEC NHH4 Plants Nitrificcation Microbes - Amino NOO3 acids * Mineralization is a key step in mmaking N available for plant growth It is dependent upon adequate soil temperatures (i.e. > 50 F) Sources of Nitrogen for Organic Ag • Storage • Recycling/Scavenging – Organic Matter – Prior crops, cereal cover • Legumes (N from air) crops – Green Manures – Meat, Fish, Blood , Feather, Bone • Vetches, clovers, peas – Alfalfa Meal – Seed Meals (cotton, soybean, etc) • Mined – Manure, Guano – Sodium nitrate – GGWtCtreen Waste Compost • Seaweed Soil Test f or Ni troge n in O rga nic Systems • There have been many ideas proposed to test soil nitroggpen to ppppredict crop response in conventional and organic production systems • In conventional production the presidedress nitrate quiktick tes t measures nitrate, the dominant formofNinthesoilform of N in the soil • In organic production nitrate is not as useful of an indicator of nitrogen due to typically low levels of nitrate encountered in soil Comparison of Organic and Conventional Onions Hollister, 1996 80 70 60 Conventional 3-N 50 OO 40 pm N pp 30 Soil 20 Organic 10 0 May May Jun Jun Jul Jul Jul Aug Smith, 1996 Soil Nitrate in Or PPd ti2 25 ro dry soil -1 20 d uc µg g 15 ti -N 3 on 10 g NO anic Vegetable 5 22001 0 - Summer-Yr1 2003 Fall-Yr1 Winter-Yr1 0-15 cm Spring-Yr1 15-30 cm Summer-Yr2 Fall-Yr2 Winter-Yr2 Spring-Yr2 Summer-Yr3 Fall-Yr3 Winter-Yr3 Jackson, 2005 Nitrogen Soil Fertility • The amino sugar soil N test has not ppgroved to be a good predictor of N availability to crops • At present: the best iindication of available soil nitrogen status in organic systems is with total nitrogen: – Soils with less than 0.07% total N mineralize limited quantities of N for rapid crop growth – Soils with more than 0.15% total N can mineralize significant amounts of N during the crop cycle Nitrogen SSoil Fertility • As an example a soill with 0.07% total N contains 2,800 lbs N/A • Incubation studies have shown that during the summer about 1% of soil organic N mineralizees/month • For a 60 day growth cycle that would be: 2800lbsNx10%x2,800 lbs N x 1.0% x 2 months = 56 lbs N/A • This is about 1 lb N/A/day Nitrogen SSoil Fertility • The nitrogen that min neralizes from the organic matter is the “background” nitrogen level that evvery soil provides for plant growth • A key goal in organicc production is to build up the levels of organic matter which increases the levels of stored N which can be mineralized for plant growth Impacts of Organic Soil Building on Nitrogen Storage in Soil Soil Type Manaagement Total Soil N % Clay Loam Organic 0.17 Clay Loam Conventional 0.14 Loam Organnic 0140.14 Loam Conventional 0.11 Fine Sandy Loam Organic 0.12 Fine S and y L oam Conventiona l 0060.06 Smith, 2003 Impacts of Organic Soil Building on Nitrogen Storage in Soil Soil Type Manaagement Total Soil N % Clay Loam Organic 0.17 Clay Loam Conventional 0.14 Loam Organnic 0140.14 Loam Conventional 0.11 Fine Sandy Loam Organic 0.12 Fine S and y L oam Conventiona l 0060.06 Smith, 2003 Generalized Trend Line: Mineral Nitrogen MMade Available from Soil Organic Matter itrogen A/Day NN // N 1.5 _ 1.0 lbs Mineral 050.5 0 10 Weeks Nitrogen Requirement of Vegetables Seasonal Uptake Low total N content Medium total N High total N content < 120 lbs /acre conntttent > 200 lbs /acre 120-200 lbs/acre Baby greens Carrrot Broccoli Beans Corn, sweet Cabbage Cucumbers Gaarlic Cauliflower Radish Lettuce Celery Spinach Mellons Potato Squashes Onion Peppers Tomatoes Nature of Veg getable Crops • Rapid growth from 30 to • High peak demand for N 60 days following • Can be as high as 44--55 lbs planting Nitrogen/Acre/day 100,000 90,000 80,000 70,000 60,000 50,000 40,000 Fresh (Lbs) Poly. (Fresh (Lbs)) 30,000 20,000 10,000 0 20 30 40 50 60 70 Crux of Nitrogenn Fertilization of Organic Horticultural Crops • Some crops may be able to achieve economicallyyp accepttable yield from mineralization of soil organic matter • Most of our key cropps will generally need greater quantities of available mineral nitrogen to achieve eeconomically viable yields Nitrogen from Green Manures • This can be an economical source of N • Cereal cover crops recycle and scavenge N from theesoile soil • Legumes fix nitrogen from the air • There are some k ey idiissues regarding N from cover crops that needs to be kept in mind Cover Crop Depends upon Proteins C:N; lignin and Polyphenols Microbes Microbes Available Typically <<1010--3030%% of cover crop N is taken up by the first subsequent Mineral Crop* Nitrogen * A good deal of cover crop N remains in the system and can can be taken up in later years (i.e. 7373%% - Jackson, 20002000)) N Release Pattern from Cover Crops 18 Legume Mix 16 Mustard Oats 14 (ppm) 12 10 l Nitrogen aa 8 6 otal Miner otal 4 TT 2 0 0112539 53 67 Days After Incorporation of Cover Crop Smith & Brennan, 2003 Nitrogen release from cover crop residue based on the N content Percent N Examples of Cover Crops Nitrogen Release in Cover Crop Will Tie up N 0.5 Cereal Straw Will Tie up N 1.0 Cereal Straw Will Tie up N 1.5 Cereal at heading May Tie up N* 2.0 Cereal pre heading May Tie up N* 2.5 Mustards at heading and Imm. cereal Will Release N 3.0 Mustards, legumes and juvenile cereal Will Release N 3.5 Legumes and immature mustards Will Release N 4.0 Legumes 2006 & 2007 Cover Crop & Fertilizer Trial Year Bi omass N in Tops N in Tops T/A Percent lbs/A 2006 3.21 3.1 194.5 2007 3371.71 212.1 153. 4 Smith and Muramoto, 2007 2006 Soil Mineral Nitrogen CCICover Crop Incorpora tion tPltiBto Planting Brocco li 12.00 With cover crop No cover crop 10.00 SEM) 8.00 mg/kg +/- (( 6006.00 4.00 ineral N MM 2.00 Total 0.00 21-FbFeb 1-Mar 9-Mar 16-Mar 23-Mar 31-Mar 6-Apr 13-Apr 20-Apr 2007 Soil Mineral Nitrogen Cover Crop Incorporation to Planting Broccoli 16. 0 14.0 /- SEM 12.0 10.0 mg/Kg + 8.0 6.0 With cover crop ineral N 4.0 mm No cover crop 2.0 Total 0.0 27‐Mar 29‐Mar 31‐Mar 2‐Apr 4‐Apr 6‐Apr 8‐Apr 10‐Apr 12‐Apr 14‐Apr Date Percent of Cover Crop Nitrogen Mineralized at 8 Weeds 40 35 30 25 20 15 10 5 0 0 1 2 3 4 5 6 -5 Hartz, unpublished 2006 Nitrogen in Broccoli Biomass lbs/A At Harvest 200.0 180.0 160.0 bs/A 140.0 120.0 100.0 omass N l ii 80.0 No cover crop 60.0 With cover crop roccoli B 40.0 BB 20.0 0.0 0 75 150 225 Organic Fertilizer Application Rate lbs N/A 2007 Nitrogen in Broccoli Biomass lbs/A At Harvest 200.0 180.0 160.0 bs/A ll 140.0 120.0 mass N 100.0 oo No cover crop 80.0 With cover crop 60.0 ccoli Bi oo 40. 0 Br 20.0 0.0 0 75 150 225 Organic Fertilizer Application Rate lbs N/A Broccoli Yield 2006 Trial 9.0 Without cover crop 8.0 With cover crop (+/-) 7.0 6.0 5.0 ns/A) SEM oo 4.0 3.0 oli yield oli yield (T cc 2.0 Broc 1.0 000.0 075150 225 Organic Fertilizer Application Rate lbs N/A Broccoli Yield 2007 Trial 10.0 9.0 Without cover crop 8.0 With cover crop (+/-) MM 7.0 6.0 ons/A) SE 505.0 TT 4.0 3.0 oli yield oli yield ( cc 2.0 Broc 1.0 0.0 075150 225 Organic Fertilizer Application Rate lbs N/A Summary of Nitrogen from Cover Crops • Cover crops can provide substantial amounts of N for plant growth • However, supplemental fertilization was needed for maximum yield • The amount and rate of nitrogen made available from the coover crop depends on its nitrogen content Mineralization of Mineral Nitrogen from Manures and Compost Manures and composts are widely used in orgaanic systems, but what can they provide with regards to nitrogen nutrition Characteristics of Compost/Manures Material Total N C/N Ratio Pelletized poultry manure 474.7 454.5 Aged poultry manure 3.1 9.1 Poultry compost 3.8 5.7 Aged feedlot manure 202.0 12.