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1 MSU Extensin Publicatin Archive Archive cpy f publicatin, d nt use fr current recmmendatins. Up-t-date infrmatin abut many tpics can be btained frm yur lcal Extensin ffice. Nitrgen Management fr Michigan Ptates Michigan State University Michigan State University Extensin S.Snapp, D. Smucker and M.Vitsh(retired), Department f Crp and Sil Sciences Issued March pages The PDF file was prvided curtesy f the Michigan State University Library Scrll dwn t view the publicatin.

2 Extensin Bulletin E-2779, Nitrgen Management fr Michigan Ptates New, March «-ras3s 2002 ' ' ^^^hft S. Snapp, D. Smucker and M. Vitsh (retired) Crp and Sil Sciences Dept. O ptimizing nitrgen (N) use achieves multiple gals. It enhances tuber quality and strability, preserves grundwater quality and minimizes csts. Matching the supply f nitrgen and plant demand is the key t imprving fertilizer efficiency. Multiple, split applicatins f nitrgen prvide a cntinuus supply that matches plant demand and insures even grwth (Table 1). Nte that Table 1 takes int accunt the nitrgen stred in the sil, yield gal and the fact that late-harvested and high N-demanding varieties (e.g., Snwden) require mre N. Table 2 shws hw plant nitrgen demand changes during the grwing seasn, and hw peak demand crrespnds with tuber initiatin and bulking. It is imprtant t d a critical assessment f nitrgen stred in the sil r supplied frm nnfertilizer surces, e.g., irrigatin water and manure. (See "nitrgen credits" discussin.) Table 1. Michigan ptat nitrgen recmmendatins, including residual sil nitrgen (Vitsh, 1990). Yield gal Lw N-demanding variety High N-demanding variety (lbs. N/acre) (cwt./acre) (lbs. N/acre) Sandy sil, n residual N 190 (pre-plant sil test inrganic N<20 ppm) Sil with residual N r rganic matter >3% (sil test inrganic N>20ppm)* * Assumes that 20 ppm x 3.0 = 60 lbs. N/acre available fr plant uptake. MICHIGAN STATE U N I V E R S I T Y EXTENSION

3 Nitrgen Management fr M i c h i g a n Ptates Table 2. Recmmendatins fr nitrgen applicatin based n grwth stages and tests fr plant nitrgen levels (Vitsh et al., 1997). Tls t determine yur nitrgen status* Develpmental stage Percent nitrgen uptake Stage I (early grwth) 15-35% Stage II (early tuber initiatin, tuberizatin) 35-45% > 14,000 > 96% Stage III (enlargement f tubers, bulking) 30-40% > 12,000 > 96% 0% > 10,000 Stage IV (tuber maturatin) Petile nitrate cncentratin (ppm, dry) Chlrphyll meter* * (% SPAD reading f windw plt, cmpared t high N) * Measured values that fall belw the minimum shwn in Table 2 suggest that the crp is N-deficient and that sidedress applicatins f N are required. * Chlrphyll readings shuld remain abve 96% fr Stage II and Stage III. M n i t r i n g n i t r g e n : Plant nitrgen can be mnitred using different tls, such as petile sap fr in-field r rapid measurements and labratry tissue nitrate tests. Chlrphyll SPAD field measurement is a technique under investigatin. It is critical t mnitr thrughut the seasn t dcument trends. Use a cnsistent technique in chsing leaves t mnitr. Check with yur labratry t determine their preferred methd. Generally, sampling shuld target fully develped leaves, such as the furth frm the tp. N i t r g e n credits: Credit shuld be given fr nnfertilizer surces f nitrgen. Irrigatin water can be readily tested t determine if nitrgen is present. If nitrate-n is present in irrigatin water, it shuld be cnsidered when calculating fertilizer requirements because it is immediately available (Figure 1). Legumes such as alfalfa and clvers supply sme nitrgen sn after incrpratin r plwdwn, and sme later in the seasn. A pr stand f alfalfa prvides abut 60 lbs. f N, whereas a credit f 130 lbs. N/acre is pssible frm a gd stand f alfalfa (Vitsh, 1990). Mature manure and cmpst generally supply nitrgen ver ne t tw years. Raw r fresh manure frm straw bedding can be assciated with ptat scab disease and shuld nt be used. Manure slurry frm lagn strage and mature manure r cmpst can build sil nitrgen levels withut increasing scab incidence. "Windw plts" can be useful t calibrate the use f N-mnitring tls. A windw plt is made by applying a reduced amunt f N in a strip acrss a field t cmpare ptat yields in the strip t the rest f the field. Used ver several years, windw plts can help ptimize yur verall Nmanagement strategy by indicating plant N status at lwer levels f N fertilizer. 2

4 N i t r g e n M a n a g e m e n t fr M i c h i g a n Ptates Figure 1. Nitrgen credits can cme frm many different s surces. This figure shws ptential availability f nitrgen frm lw and high quality surces. Subtract the estimated est amunt available frm the ttal nitrgen recmmended. i n Manure r cmpst ^ ^ ^ ^ Cver crp, cereal ^ ^ \ ^ / ^^ Hay rtatin ^9 ^x Cver legume 1 Cver crp, crp, legume Irrigatin water N ^z^zz^f^^ (0 >O C S/ 5 \ -- a **m? 5 z ( Water management: Careful irrigatin Benefits f precisin N management: scheduling s as nt t exceed the seasnal evaptranspiratin rate by mre than five inches will maximize yield, N efficiency and specific gravity ptential. Rainfall is difficult t predict, but shuld be taken int accunt when pssible. Excess rain received early in the grwing seasn can leach nitrgen belw the rt zne. Fertilizer with ammnium as an N surce (e.g., ammnium sulfate r ammnium nitrate) can help reduce leaching lsses. Planting deep-rted cver crps, such as rye, can als help recver leached N. Nitrgen rates need t be matched clsely t plant demand. In extensive n-farm research cnducted frm , nitrgen efficiency was increased 50 percent t 67 percent, and ptential nitrgen leaching lss reduced frm 135 lbs. t 50 lbs. This data (Figure 2) is frm 3 years f n-farm trials. Nitrgen fertilizer was reduced by mre than 70 lbs./acre withut reducing tuber yields. 3

5 N i t r g e n M a n a g e m e n t fr M i c h i g a n Ptates Figure 2. Average f three years f data frm Michiga^ptat prducers (20 n-farm trials). N fertilizer rate can be cut by 70 lbs. withut reducing yields (Vitsh, et al., 1997). 450 i References: Vitsh, M.L., Ptat Fertilizer Recmmendatins. MSU Extensin Bulletin E pp. Mderate N (mean 190) High N (mean 260) Vitsh, M.L.; Paul, E.A.; Harwd, R.R. and Smucker, D.R., Nitrgen stewardship practices t reduce nitrate leaching and sustain prfitability in an irrigated ptat prductin system. In: R. Chase (Ed.) 1997 Michigan Ptat Research Reprt Vl. 29, MSU and MPIC, Dewitt, Mich., pp N fertilizer rate (lbs./acre) MICHIGAN STATE \ I V E R S EXTENSION Yield (cwt/acre) N lss (Ibs./acre) MSU is an affirmative-actin, equal-pprtunity institutin. Michigan State University Extensin prgrams and materials are pen t all withut regard t race, clr, natinal rigin, gender, religin, age, disability, plitical beliefs, sexual rientatin, marital status, r family status. Issued in furtherance f Extensin wrk in agriculture and hme ecnmics, acts f May 8 and June 30, 1914, in cperatin with the U.S. Department f Agriculture. Margaret A. Bethel, Extensin directr, Michigan State University, E. Lansing, MI This infrmatin is fr educatinal purpses nly. References t cmmercial prducts r trade names d nt imply endrsement by MSU Extensin r bias against thse nt mentined. This bulletin becmes public prperty upn publicatin and may be printed verbatim with credit t MSU. Reprinting cannt be used t endrse r advertise a cmmercial prduct r cmpany. New 3/02-2M-KMF-BRD,.70, fr sale nly 4