Number 174 January 23, 2009

Transcription

1 Numer 174 Jnury 3, The effects of residue removl on soil nd wter qulity 1. Weed control strtegies in grin sorghum 4 3. The vlue of soil profile nitrogen testing 6 1. The effects of residue removl on soil nd wter qulity Crop residue is in high demnd in some res of Knss nd other sttes, either s feedstocks for cellulosic ethnol production, industril uses, livestock feed, or other uses. Producers cn get pid for selling their crop residue for these uses. But is it relly good ide to remove nd sell crop residue? Wht is the cost of crop residue removl in terms of loss of soil qulity nd productivity, nd potentil impirment of surfce wter qulity? Leving crop residue on the soil surfce is the est nd simplest wy of reducing wter nd wind erosion. Widespred residue removl for expnded uses my ccelerte soil erosion nd increse the loss of sediments, nutrients, nd pesticides in runoff wter. Sediment nd nutrients leving griculturl soils in runoff wter re the min non-point source (NPS) pollutnts of downstrem wter odies, such s ponds, reservoirs, strems, nd rivers. But crop residue removl my not e ll-or-nothing. The producer my wnt to remove some residue nd leve some. How much residue cn e removed from crop fields without creting erosion nd runoff prolems? The nswer is not fully known, nd prtilly depends on the level of crop productivity. In some cses, prticulrly in semirid regions such the Gret Plins, not enough residue is produced most yers to protect soil from wter nd wind erosion nd mintin dequte levels of soil orgnic mtter. In those cses, ny removl of residues my further degrde soil qulity, increse wter pollution, nd reduce crop production. A study ws conducted to ssess on-frm impcts of vrile rtes of residue removl from whet nd sorghum fields on wter erosion in two soils ner Hys in lte Fll, 008. A 0-yer no-till field under continuous winter whet nd 3-yer conventionl-till grin sorghum field (plowed in the spring efore plnting) were selected. The soil in oth fields is silt lom with slope of 6% for whet nd 3% for sorghum. 1

2 The stule remining fter hrvest ws removed t 0, 5, 50, 75, nd 100%. The verge height of the stnding stule ws 1 inches for whet nd 3 inches for sorghum. The plots were prllel to the dominnt slope. Simulted rinfll ws pplied to the plots to give the effect of rinstorm with return period of 5 yers for western Knss. In ddition, second set of plots within ech field ws estlished y tilling the soil few dys efore rinfll simultion. Concentrtions of sediment, soil orgnic cron, nd nutrients in runoff were mesured. Results of this study showed tht whet nd sorghum residue removl fter hrvest exponentilly incresed loss of sediment, soil orgnic cron, nd nutrients in runoff regrdless of tillge system (Fig. 1A through B). The single rinstorm of high intensity cused lrge nd immedite runoff loss of sediment nd nutrient pollutnts when residues were removed. Where most or ll of the residue ws left intct fter hrvest, the runoff wter fter the high-intensity rinstorm ws clerer. Where hlf the residue ws removed, sediment loss incresed fter the rinstorm. Freshly tilled whet plots (tilled immeditely fter the residue removl) lost more sediment, soil orgnic, nd nutrients thn no-till whet plots for the sme level of residue removl, suggesting tht residue removl in comintion with intensive tillge cn ccelerte soil erosion to unsustinle levels. Differences in soil slope ffected the mount of pollutnts lost in runoff. More runoff, sediment, soil orgnic cron, nd nutrients were lost from the freshly-tilled whet plots with 6% soil slope (Fig. 1A) thn from the sorghum tilled field with only 3% soil slope (Fig. 1B). Sediment Loss (Tons per cre) c d Freshly Tilled No-Till Whet Field Soil Slope: 6% c cd c A d Plow Tillge Sorghum Field Soil Slope: 3% cd B Rte of Whet Residue Removl (%) Rte of Sorghum Residue Removl (%) Fig. 1. Influence of whet (A) nd sorghum (B) residue removl on sediment loss in two soils in western Knss. Mens followed y the sme lowercse letter within the sme tillge level re not significntly different.

3 Another finding, which my surprise mny, ws tht removing 75% or more of the residue fter hrvest cn negte mny of the enefits of no-till in reducing runoff. We found tht the loss of NPS pollutnts from no-till soils ws equl to those from plowed soils when residues were removed t or ove 75% (Fig. 1A). This indictes tht no-till my e no etter thn plow tillge if residues re removed t high rtes. Excessive residue removl from no-till soils cn negte the erosion control enefits ttriuted to no-till. No-till enefits for controlling soil erosion re quickly lost when residue is removed t rtes ove 5%. Residue cover is needed to keep the soil in plce. Removing residue fter hrvest lso hs negtive effect on soil cron, even in no-till whet systems (Fig. A). The lrge losses of soil orgnic cron with residue removl t rtes s low s 50% indicte tht single rinstorm of high intensity could eliminte ll the gins in soil orgnic cron pool ttriuted to no-till. Soil Orgnic Cron (Tons per cre) A c c c Totl N (Tons per cre) 3 1 B Rte of Whet Residue Removl (%) Rte of Whet Residue Removl (%) Fig.. Men loss of A) sediment-ssocited soil orgnic cron nd ) totl N in runoff under different levels of post-hrvest whet residue removl in no-till system. Mens followed y the sme lowercse letter within the sme tillge level re not significntly different. The lrge losses of soil orgnic cron with sediment my hve lrge soil, gronomic, nd environmentl implictions. Soil orgnic cron is essentil to increse the soil s ility to sor nd filter NPS pollutnts nd improve soil productivity. Residue removl lso incresed losses of essentil nutrients, prticulrly totl N (Fig. B) nd totl P. Loss of nutrients in runoff incresed with residue removl ove 50% in no-till whet. Residue removl reduces nutrient pools through two pthwys: 1) nutrient removl with residues nd ) vi incresed runoff. 3

4 Results of this study show tht crop residues re indeed essentil to reduce sediment, soil orgnic cron, nd nutrient loss in runoff, regrdless of tillge system. Crop residue removl is not recommended if soil nd wter conservtion, NPS pollution control, nd soil cron uildup re high priorities. Residue left on the soil surfce protects the soil ginst impcting rindrops, helps mintin the integrity of soil ggregtes, nd improves rin wter infiltrtion. A smll frction (out 5%) of residue my e ville for removl from no-till soils, ut further studies monitoring of pollutnts losses under different scenrios of rinfll intensities nd soil/topogrphic chrcteristics re needed to determine the mount of hrvestle residue. This project ws funded y the Knss Deprtment of Helth nd the Environment, nd U.S. EPA Section 319 Grnt Progrm through the Knss WterLINK inititive. -- Humerto Blnco, Soil Mngement, Agriculturl Reserch Center-Hys hlnco@ksu.edu -- Dn Devlin, Environmentl Qulity Specilist ddevlin@ksu.edu (Editor s Note: The following two rticles re from presenttions mde t the 009 Cover Your Acres Winter Conference, held Jn. 0-1 in Oerlin.). Weed control strtegies in grin sorghum Severe grss nd rodlef weed pressure cn reduce grin sorghum yields y 55% or more, nd mke hrvest very difficult. Good crop rottion nd hericide selection re essentil components of mnging weeds in grin sorghum. In whet-sorghum-fllow rottion, it is essentil tht rodlef nd grssy weeds do not produce seed during the fllow period hed of grin sorghum plnting. It is eqully importnt tht winter nnul grsses re not llowed to hed in spring, efore the sorghum is plnted. Fll-pplied trzine cn reduce erly-spring weed pressure hed of sorghum plnting. If winter nnul grsses re present t the time of the fll ppliction, the ddition of glyphoste to trzine will roden the spectrum of weed control. When fll-pplied hericides re not used, n erly urndown opertion the following spring is lmost lwys essentil. Essentil moisture nd nutrients will e used y weeds if the first urndown opertion is delyed too long. Delying the first urndown opertion llows weeds to grow nd some species, such s kochi, Russin thistle, nd common lmsqurters, will ecome incresingly difficult to control. Also, winter nnul grsses cn hed nd produce vile seed if the urndown is delyed too long. In sorghum, the est choice of hericides will depend on the weed species present. Brodlef weeds generlly cn e controlled with comintion of preemergence nd postemergence 4

5 hericides. With the development of hericide-resistnt weeds, however, this is ecoming incresingly difficult. Control of pigweeds in sorghum is n incresing concern cross the stte. Using soil-pplied chlorcetmide hericide with trzine (such s Bicep II Mgnum, Bicep Lite II Mgnum, Bullet, Lrit, Gurdsmn Mx, G-Mx Lite, Degree Xtr, or generic equivlents of these products) will often id in controlling pigweeds. Some of the rodlef escpes producers cn expect when using the chlorcetmide/trzine mixtures re devilsclw, puncturevine, morningglory, trzine-resistnt kochi, nd trzine-resistnt pigweeds. Using product such s Lumx preemergence, which contins mesotrione (Cllisto), will help control the trizineresistnt pigweeds nd kochi. The chlorcetmide/trzine hericides will lso do very good jo of controlling most nnul grssy weeds. A wekness of ll soil-pplied progrms is tht rinfll is required for ctivtion. Without ctivtion, poor rodlef nd grss control cn e expected. Grss control in sorghum cn e difficult tsk in mny cses. If field hs severe shttercne pressure, plnting grin sorghum is not recommended. For other nnul grssy weeds, it will e importnt to pply one of the chlorcetmide hericides. Grsses tht emerge efore the soilpplied hericides re ctivted will not e controlled. There re no hericides currently leled for postemergence grss control in grin sorghum. Although trzine nd Prmount hve grss ctivity nd cn control tiny grss seedlings, it s generlly not good prctice to depend on these hericides for grss control. K-Stte hs recently relesed lines of grin sorghum tht re resistnt to ALS hericides (such s Stedfst, Finesse, Glen, Pursuit, nd mny others) nd the ACCse hericide Select. When commercil hyrids with these hericide-resistnt trits re on the mrket, hopefully y 011 or 01, producers will hve new opportunities for postemergence grss control. Postemergence rodlef weed control hericides re ville for grin sorghum. These products will e most effective when pplied in timely mnner. Weeds tht re -4 inches tll will e much esier to control tht weeds thn re 6-8 inches tll, or lrger. Controlling weeds in timely mnner will result in less weed competition with the crop compred to witing too long to control the weeds. Atrzine comintions with Bnvel,,4-D, Buctril, or Aim (or generic versions of these hericides) cn provide excellent rod-spectrum weed control. The presence of certin weed species will ffect which postemergence hericide progrms will e most effective. See the grin sorghum section in the K-Stte 009 Chemicl Weed Control Guide (SRP 1007) to help mke the selection: The crop stge t the time of postemergence hericide pplictions cn e criticl to minimize crop injury. Delyed pplictions risk injury to the reproductive phse of grin sorghum, thus incresing crop injury nd yield loss from the hericide ppliction. Timely pplictions not only enefit weed control, ut cn increse crop sfety. Alwys red nd follow lel guidelines. -- Curtis Thompson cthompso@ksu.edu 5

6 3. The vlue of soil profile nitrogen testing Using profile nitrogen (N) test to verify N credits cn provide vlule informtion to producers. Most producers re unwre of the mount of N tht my e present in their soils from the previous seson. Plnt ville N cn e present in the soil from fertilizer crryover, previous mnure pplictions, or legume plowdowns. Fertilizer N is pplied sed on production conditions nd estimted yield potentil. When the ctul crop yield is lower thn expected, or fertilizer N ws over-pplied, there is high proility of some residul N eing present in the soil. Under conditions of high rinfll, this N is prone to losses y leching or denitrifiction. However, under conditions of low precipittion, this N will likely sty in the soil nd ecome ville for following crops. Deep nitrte-n soil testing (4-inch profile) cn provide informtion regrding the level of crryover N. Soil nitrte testing cn e especilly importnt fter crop filure due to drought conditions. Crop growth cn e extremely limited during drought, nd therefore the pplied fertilizer N, s well s minerlized soil N, is typiclly not fully utilized. This crryover N would e ville for the next crop nd in some cses, fertilizer N needs cn e significntly reduced. The reltive vlue of the profile nitrte test will depend on severl fctors ffecting N crryover. Some of these fctors include soil texture, rinfll, tempertures, crop rottion, nd mnure ppliction history. Proper soil smpling nd testing is very importnt for good ssessment of residul soil nitrte. Annul smpling of ech field is necessry for ccurte residul N estimtions. Annul smpling lso helps evlute current fertilizer ppliction progrms, providing informtion for fine-tuning future fertilizer pplictions. The key to good soil test results is proper smpling protocol. Ech smple should contin 15 to 0 cores of soil from resonly uniform re of pproximtely 40 cres. Producers who wnt more detiled informtion my wnt to reduce the re represented y ech smple. Lrge fields should e roken into smpling units sed on crop, yield, nd fertilizer histories. When tking smples for nitrte nlysis, lte fll or erly spring is good time to smple. Nitrte levels will fluctute somewht through the yer, depending on soil tempertures nd soil minerliztion rtes. The est time to tke the smple is during cool periods fter the previous crop hs een hrvested ut efore the soil wrms up too much the following spring. This will give producers good reding on how much N remins from the previous crop, efore minerliztion egins to increse nitrte levels. In ddition to residul profile nitrte, minerlized N from soil orgnic mtter is lso credited y the K-Stte soil testing l, nd mny other ls. For wrm-seson crops, the credit given y the soil testing l t K-Stte is pproximtely 0 pounds of ville N per cre during the crop yer for ech one percent of soil orgnic mtter. For cool-seson crops, the credit is pproximtely 10 pounds of ville N for ech percent soil orgnic mtter. Informtion regrding the level of soil orgnic mtter cn significntly improve the efficiency of N mngement. The smpling depth for orgnic mtter is 6 inches, which is sme s the smpling depth for phosphorus nd potssium. 6

7 A. Profile N tests re most vlule under the following conditions: * Medium- to fine-textured soils * Recent history of excessive N rtes * The previous crop hd lower-thn-expected yields * The field ws fllow the prior yer * There ws drought the prior yer * A stnd of lflf or clover hs recently een on the field * There is history of mnure ppliction * Previous yers hve hd wrm, lte flls nd/or wrm, erly springs B. Profile N tests re less likely to find residul N in the soil under the following conditions: * Sndy soils * Previous N rtes hve een pproprite or insufficient for crop yields * The immedite previous crop ws soyens * The previous yer hd excessive precipittion * No mnure or iosolids hve een pplied * Higher intensity crop rottions hve een used -- Dorivr Ruiz Diz, Nutrient Mngement Specilist ruizdiz@ksu.edu These e-updtes re regulr weekly item from K-Stte Extension Agronomy nd Steve Wtson, Agronomy e- Updte Editor. All of the Reserch nd Extension fculty in Agronomy will e involved s sources from time to time. If you hve ny questions or suggestions for topics you'd like to hve us ddress in this weekly updte, contct Steve Wtson, swtson@ksu.edu, or Jim Shroyer, Reserch nd Extension Crop Production Specilist nd Stte Extension Agronomy Leder jshroyer@ksu.edu 7