CMG GardenNotes #231 Plant Nutrition. Fertility and Fertilization

Transcription

1 CMG GardenNtes #231 Plant Nutritin Outline: Fertility and fertilizers, page 1 Plant nutrients, page 2 Clrad sils and plant nutritinal needs, page 3 Nitrgen, page 3 Irn, page 4 Phsphrus, page 5 Ptassium, page 5 Zinc, page 6 Fertility and Fertilizatin Many peple cnfuse plant nutritin with plant fertilizatin. Plant nutritin refers t the need fr basic chemical elements fr plant grwth. The term fertilizatin refers t the applicatin f plant nutrients t supplement the nutrients naturally ccurring in the sil. Nutrients may be applied as cmmercially manufactured fertilizers, rganic fertilizers and/r ther sil amendments. Organic fertilizers and sil amendments are typically lw in plant-available nutrient cntent. Fr additinal infrmatin abut fertilizers and sil amendments, refer t the CMG GardenNtes #232, Understanding Fertilizers, and #241, Sil Amendments. Adequate sil fertility is nly ne f the many sil-related grwth factrs. Fertilizers will increase desirable plant grwth nly if the plant is deficient in the nutrient applied and ther grwth factrs are nt als significantly limiting plant grwth. Fertilizatin will nt cmpensate fr pr sil preparatin, the lack f water, weed cmpetitin and ther nn-nutrient grwth limiting factrs! Fertilizatin will nt enhance desired grwth if the nutrients applied are nt deficient. Frm a nutritinal perspective, a plant cannt tell if applied nutrients cme frm a manufactured fertilizer r a natural surce. Plants use nutrients in inic frms. Sil micrrganisms must break dwn rganic sil amendments, rganic fertilizers and many manufactured fertilizers befre the nutrients becme usable by plants. Frm a nutritinal perspective, the primary difference between manufactured and rganic sil amendments/rganic fertilizers is the speed at which nutrients becme available fr plant use. Manufactured fertilizers release rates are typically, but nt always, a few days t weeks. Sme are specially frmulated as cntrlled 231-1

2 release, slw release r time release prducts release ver a perid f mnths, but sme rganic fertilizers are quickly available. With natural-rganic fertilizer, nutrients typically becme available ver a perid f mnths r years. Hwever, there are exceptins t this general rule. High salt cntents f sme manufactured fertilizers and sme rganic sil amendments can slw the activity f beneficial sil micrrganisms and subsequent nutrient release. Benefits f rganic fertilizers and sil amendments include imprvements in sil tilth (suitability f the sil t supprt plant grwth). This shuld nt be cnfused with fertilizatin, a distinctly different sil management bjective. Remember that fertility is nly part f the sil s rle in supprting plant grwth. The rganic cntent f the sil als directly affects plant grwth due t its influence n sil tilth and the activity f beneficial sil micrrganisms. Relying slely n manufactured fertilizers is nt recmmended as this des nt supprt gd sil tilth. Plant Nutrients Plants need 17 elements fr nrmal grwth. Carbn, hydrgen, and xygen cme frm the air and water. Sil is the principle surce f ther nutrients. Primary nutrients (nitrgen, phsphrus, and ptassium) are used in relatively large amunts by plants, and ften are supplemented as fertilizers. [Table 1] Secndary nutrients (calcium, magnesium, and sulfur) are als used in large amunts but are typically readily available and in adequate supply. Micrnutrients r trace elements are needed nly in small amunts. These include irn, zinc, mlybdenum, manganese, brn, cpper, cbalt, and chlrine. [Table 1] Table 1. Essential Plant Nutrients Nutrient Ins Absrbed by Plants Structural elements Carbn, C CO2 Hydrgen, H H2O Oxygen, O O2 Primary nutrients Nitrgen, N NO3 -, NH4 + Phsphrus, P H2PO4 -, HPO4-2 Ptassium, K K + Secndary nutrients Calcium, Ca Ca +2 Magnesium, MG Mg +2 Sulfur, S SO4-2 Micrnutrients Brn, B H2BO3 - Chlrine, Cl Cl - Cbalt, C C +2 Cpper, Cu Cu +2 Irn, Fe Fe +2, Fe +3 Manganese, Mn Mn +2 Mlybdenum, MO MO4-2 Zinc, Zn Zn

3 Rts take up nutrients primarily as ins disslved in the sil s water. The ins may be psitively charged (catins) r negatively charged (anins). The nutrient in sup in the sil s water is in a cnstant state f flux as the variety f ins disslve in and precipitate ut f slutin. Clay particles and rganic matter in the sil are negatively charged, attracting the psitively charged catins (like ammnium, NH 4 +, and ptassium, K + ) and making the catins resistant t leaching. Negatively charged anins (like nitrate, N0 3- ) are prne t leaching and can becme a water pllutin prblem. Bth ammnium and nitrate are imprtant plant nitrgen surces and are cmmnly fund in salt frms in fertilizers. The Catin Exchange Capacity, CEC, is a measurement f the sil s capacity t hld catin nutrients. Mre precisely, it is a measurement f the capacity f the negatively charged clay and rganic matter t attract and hld psitively charged catins. CEC is useful in cmparing the ptential fr different sils t hld and supply nutrients fr plant grwth. Clrad Sils and Plant Nutritinal Needs Nitrgen Nitrgen is the ne nutrient mst ften limiting plant grwth. The need fr nitrgen varies frm plant t plant. Fr example, tmates and vine crps (cucumbers, squash, and melns) develp excessive vine grwth at the expense f fruiting with excess nitrgen. Ptates, crn and cle crps (cabbage, brccli, and cauliflwer) are heavy feeders and benefit frm high sil nitrgen levels. Bluegrass turf and many annuals als benefit frm rutine nitrgen applicatins. Trees and shrubs have a lw relative need fr sil nitrgen. Clrad sils benefit frm nitrgen fertilizatin f the right amunt and frequency t meet plant needs. General symptms f nitrgen deficiency are shwn in Table 2 and Figure 1. Table 2 and Figure 1. Symptms f Nitrgen Deficiency Leaves Unifrm yellwish-green Mre prnunced in lder leaves Small, thin leaves Fewer leaflets High fall clr Early leaf drp Shts Shrt, small diameter May be reddish r reddish brwn Sil tests have limited value in indicating nitrgen needs fr a hme garden r lawn because the value is cnstantly changing due t rganic cntent, micrrganism activity, and changes in temperature and water. Nitrgen is useable by plants in tw frms, ammnium (NH 4+), and nitrate (NO 3- ). Ammnium, being psitively charged, is attracted t the negatively 231-3

4 charged sil particles and thus is resistant t leaching (mvement dwn thrugh the sil prfile). Sil micrrganisms cnvert ammnium t nitrate. Nitrate, being negatively charged, readily leaches belw the rt zne with excess rain/irrigatin in sandy sils. Prevent water pllutin by aviding ver-fertilizatin f nitrgen, particularly n sandy sils. Sil micrrganisms release nitrgen tied-up in rganic matter ver a perid f time. Release rates frm cmpst are very slw (i.e., ver a perid f years). The need fr nitrgen fertilizer is based n the rganic cntent f the sils. [Table 3] Table 3. Need fr Nitrgen Fertilizer Based n Sil Organic Cntent Sil Organic Cntent Rutine Applicatin Rate Fr Gardens 1% 2 punds actual N / 1000 square feet 2-3% 1 pund actual N / 1000 square feet 4-5% 0 Irn Irn chlrsis refers t a yellwing f leaves caused by an irn deficiency in the leaf tissues. Primary symptms include interveinal chlrsis (i.e., a general yellwing f leaves with veins remaining green). Symptms appear first and are mre prnunced n yunger leaves and n new grwth. In severe cases, leaves may becme pale yellw r whitish, but veins retain a greenish tint. Angular shaped brwn spts may develp between veins and leave margins may scrch (brwn alng the edge). Symptms may shw n a single branch r n the entire tree. General symptms f irn chlrsis are shwn in Table 3 and Figure 2. Table 3 and Figure 2. Symptms f Irn Chlrsis Leaves General yellwing f leaf with veins remaining green Mre prnunced in yunger leaves and new grwth Angular brwn spts and marginal scrch Smaller Curl, dry up and fall early Branches May shw n a single branch r the entire plant In western, high ph sils, irn is nt deficient; but rather unavailable fr plant uptake due t the sil s high lime (calcium carbnate) cntent. In western sils, irn chlrsis is a general symptm f ther prblems, including the fllwing: 231-4

5 Springtime ver-watering is the primary cause f irn chlrsis in western sils! Attentin t irrigatin management, with seasnal changes f the irrigatin cntrller will generally crrect irn chlrsis. Sil cmpactin and lw sil xygen cntributes t irn chlrsis. Irn chlrsis is an early symptm f trunk girdling rts. Irn chlrsis appears as a cmplicatin f winter trunk/bark injury. Attentin t these cntributing factrs is much mre effective than adding irn prducts. Fr additinal details n dealing with irn chlrsis, refer t CMG GardenNtes #223, Irn Chlrsis. Phsphrus Nte: Phsphrus, P, is a primary nutrient in plant grwth. The wrd phsphate, P2O5, refers t the inic cmpund cntaining tw atms f phsphrus and five atms f xygen. The phsphrus cntent f fertilizer is measured in percent phsphate. Phsphrus may be present in high cncentratins, hwever it may nt be in a plant available frm. Deficiencies are mst likely t ccur in new gardens where the rganic matter cntent is lw and the sil has a high ph (7.8 t 8.3). A sil test is the best methd t determine the need fr phsphrus fertilizers. Phsphrus is als less available t plants when sil temperatures are cl. In the spring, the use f starter fertilizers with phsphrus may be beneficial t herbaceus flwers and vegetable transplants. Phsphrus deficiency is difficult t diagnse, because ther grwth factrs will give similar symptms. General symptms include sparse, green t dark green leaves. Veins, petiles, and lwer leaf surface may be reddish, dull brnze, r purple, especially when yung. Phsphrus deficiency may be bserved n rses in the early spring when sils are cld, but the cnditin crrects itself as sils warm. Excessive phsphrus fertilizer can aggravate irn and zinc deficiencies and increase the sil salt cntent. Many hme gardener sils are significantly ver fertilized with phsphates, aggravating sil salts and irn chlrsis. Typically the ver fertilizatin results frm ver applicatin f cmpsts. Ptassium Nte: Ptassium, K, is a primary nutrient in plant grwth. The wrd ptash, K2O, refers t the inic cmpund cntaining tw atms f ptassium and ne atm f xygen. The ptassium cntent f fertilizer is measured in percent ptash. Ptassium levels are naturally adequate and even high in mst Clrad sils. Deficiencies ccasinally ccur in new gardens lw in rganic matter and in sandy sils lw in rganic matter. A sil test is the best methd t determine the need fr ptassium fertilizers. Ptassium deficiency is very difficult t diagnse, because ther grwth factrs will give similar symptms. General symptms include a marginal and interveinal chlrsis (yellwing), fllwed by scrching that mves inward. Older leaves are 231-5

6 affected first. Leaves may crinkle and rll upward. Shts may shw shrt, bushy, zigzag grwth, with dieback late in seasn. Excessive ptash fertilizer can aggravate sil salt levels. Many hme garden sils are ver fertilized with ptash, leading t salt prblems. Zinc Zinc deficiency ccasinally ccurs in sandy sils cntaining excessive lime and in sils lw in rganic matter (typical f new yards where the tpsil has been remved). Excessive phsphate fertilizatin may aggravate a zinc prblem. It will be seen mre in years with cld wet springs. Sweet crn, beans, and ptates are the mst likely vegetables t be affected. Symptms include a general stunting f the plant due t shrtening f interndes (stem length between leaves). Leaves n beans typically have a crinkled appearance and may becme yellw r brwn. On yung crn, symptms include a brad band f white t-translucent tissue n bth sides f the leaf midrib starting near the base f the leaf, but generally nt extending t the tip. Occasinal manure applicatins will supply the zinc needs. If a sil test indicates zinc deficiency (less than 1 ppm), apply a zinc-cntaining fertilizer accrding t label directins. Additinal Infrmatin CMG GardenNtes n Sils, Fertilizers and Sil Amendments: #211 Intrductin t Sils #232 Understanding Fertilizers #212 The Living Sil #233 Calculating Fertilizer Rates #213 Managing Sil Tilth #234 Organic Fertilizers #214 Estimating Sil Texture #241 Sil Amendments #215 Sil Cmpactin #242 Using Manure #218 Earthwrms # 243 Using Cmpst #219 Sil Drainage #244 Cver Crps and Green Manure Crps #221 Sil Test #245 Mulching with Wd/Bark Chips, Grass #222 Sil ph Clippings and Rck #223 Irn Chlrsis #246 Making Cmpst #224 Saline Sils #251 Asking Effective Questins Abut Sils #231 Plant Nutritin Authrs: David Whiting (CSU Extensin, retired), Adrian Card (CSU Extensin), Carl Wilsn (CSU Extensin, retired), and Jean Reeder, Ph.D., (USDA-ARS, retired). Revised by Dan Gldhamer (CSU Extensin). Artwrk by David Whiting; used by permissin. Clrad Master Gardener GardenNtes are available nline at Clrad Master Gardener training is made pssible, in part, by a grant frm the Clrad Garden Shw, Inc. Clrad State University, U.S. Department f Agriculture and Clrad cunties cperating. Extensin prgrams are available t all withut discriminatin. N endrsement f prducts mentined is intended nr is criticism implied f prducts nt mentined. Cpyright Clrad State University Extensin. All Rights Reserved. CMG GardenNtes may be reprduced, withut change r additins, fr nnprfit educatinal use. Revised Octber 2014, Octber