Ecological Intensification of Corn-Based Cropping Systems

Transcription

1 Ecologicl Intensifiction of Corn-Bsed Cropping Systems D. Wlters, K. Cssmn, A. Doermnn, M.A.A. Adviento-Bore, A. Lisk, J. Specht, nd H. Yng Deprtment of Agronomy nd Horticulture, University of Nersk, PO Box , Lincoln NE ; emil Introduction Meeting the projected glol demnd for food nd fuel from corn systems while conserving nturl resources nd improving environmentl qulity cn only e chieved y the intensifiction of existing corn systems (Cssmn, 1999; Cssmn et l., 2003). Yield nlysis of the centrl U.S. corn-elt indictes tht there is lrge exploitle yield gp for corn. Since 1999 we hve een experimenting with optimizing corn mngement systems to exploit corn yield potentil. To dte, our experience hs shown tht considerle yield increses re relized y choosing the right comintion of dpted vrieties, plnting dte nd plnt popultions to mximize crop productivity. In ddition, more intensive N mngement strtegies tht focus oth on improving crop N use efficiency nd residue cron mngement lso contriute to reducing nitrogen input over the longer-term through increses in soil orgnic mtter nd N storge tht cn increse the indigenous soil N supply cpcity. In ddition, intensifiction hs not resulted in significnt increses in the glol wrming potentil of these cropping systems. Yield potentil Corn yield potentil represents the mximum chievle grin yield of n dpted cultivr or hyrid when grown with miniml iotic or iotic stresses. Here the only limittions re temperture, solr rdition nd genetics. How do we mesure yield potentil for given region? Tht is est done y cultivting the crop in field experiments under optiml mngement without nutrient or wter limittions nd creful control of diseses, insect pests nd weeds. An lternte nd more convenient mens of estimting yield potentil is with well clirted mechnistic simultion models. Figure 1 shows timeline of Ntionl Corn Growers Assocition yield contest winners for the irrigted nd rinfed ctegories with oth first nd second plce winners in ech yer. Except for the period, nd the most recent yer in 2007, the first nd second plce yields re very similr nd the gp etween irrigted nd rinfed yields hs nrrowed owing to etter dpted, more stress resistnt cultivrs (Duvick nd Cssmn, 1999). The outliers in were the yields reported y Frnces Childs from Mnchester Iow, which could not e verified y simultion using the ctul corn hyrid nd climte dt t this site (Yng et l., 2004), nd which were susequently disqulified ecuse the stndrd yield verifiction procedures used t this site did not follow contest guidelines. In fct, Mr. Childs ws susequently ccused of cheting in court cse (Wterloo-Cedr Flls Courier, 2004). The 2007 yields for the irrigted ctegory lso pper to e suspicious in tht they re well ove the trend line of the pst 18 yers (excluding the disqulified yields from ). Moreover, oth the first nd second plce yields from 2007 come from the sme frmer. Until these yields cn e verified with

2 roust crop simultion model, we do not elieve they cn e relied upon s evidence tht the yield plteu hs een roken for winning yields in the irrigted clss. Insted, we elieve tht corn yield potentil for the irrigted ctegory hovers round the u/ rnge which identifies this s the prole yield ceiling, except in yers with exceptionl climte stress, such s the unusully high tempertures of the 1988 growing seson. Figure 2 shows similr exercise wherey yield potentil is estimted with the Hyrid-mize model (Yng et l., 2004) over wide rnge of sites within the U.S. corn-elt. Bsed upon these simultions, ceiling-yield for corn yield potentil is estimted to e in the sme rnge s the NCGA contest winners, excluding the disqulified yields nd the most recent 2007 yield. The model simultion indictes tht minimum of 60 dys of reproductive growth is needed to chieve this yield potentil. Hence, normlly hot yers would limit corn yield potentil due to rpid GDD ccumultion nd shortened grinfilling period. These dt lso suggest tht limittions in nutrient mngement, plnt popultion nd disese suppression hve limited verge Corn Belt frm yields to 60% of yield potentil. At issue is whether closing this yield gp cn e chieved in sustinle fshion with miniml environmentl impct nd without incresing GHG emissions from griculturl lnd. To ssess such options requires full ccounting of the glol wrming potentil (GWP) of griculturl systems including the net chnges in soil orgnic cron (SOC), the energy consumed in crop production nd the trce gs emissions (notly N 2 O) ssocited with N mngement. Corn yield (u/cre) Irrigted 1st Irrigted 2nd Non-irrigted 1st Non-irrigted 2nd Frncis Childs (Non-irrrigted) Yer Figure 1. Yield trend for irrigted nd non-irrigted corn yield contest winners of the NCGA through 2007.

3 330 Men yield potentil (u/cre) Length of reproductive growth (d) Figure 2. Hyrid-Mize simulted corn yield for 80 loctions cross the U.S. corn-elt within Lt N; Long W; Elev m. Hyrid: 2650 GDU (110 d CRM); Plnting dte: My 1, 40,000 plnts/cre. Mngement: no limittions y wter or nutrients. The Ecologicl Intensifiction Experiment In order to ddress these questions, long-term experiment ws estlished in 1999 in Lincoln, NE. The primry ojective of this experiment is to evlute resource-efficient mngement concepts for chieving crop yields tht pproch the climtic yield potentil. The soil t this site is deep Kenneec silty cly lom with high soil fertility sttus (ph 6 to 6.5, 2.5 to 3% orgnic mtter, 300 to 400 ppm K, nd ppm Bry P-1 P) The experiment is conducted with three crop rottions s min plots (CC- continuous corn, CS or SC corn soyen rottion with n entry point into ech crop in ech yer), three plnt popultions densities s su-plots nd two levels of nutrient mngement (recommended nd intensive) s the finl split. For this pper, four mngement systems re evluted, CCrecommended mngement, CC-intensive mngement, CS-recommended nd CS-intensive. Tle 1 summrizes the rnge in nutrient mngement, popultion nd yield for these tretments through Averge crop yields in this experiment were close to the yield potentil of soyen nd corn t this loction nd significntly higher thn the ntionl or stte verge. Corn yields were generlly in the 215 to 287 u/ rnge or within 84 to 97% of the simulted yield potentil. Corn following soyen yielded out 5 to 11% higher thn continuous corn primrily due to fewer prolems with stnd estlishment nd fewer pest nd disese prolems.

4 Tle 1. Crop mngement prctices nd grin yields in continuous corn (CC) nd corn/soyen rottion (CS) systems with recommended (-rec) or intensive (-int) mngement ( ). CS-Rec CS-Int CC-Rec CC-Int Yield gol (% of yield potentil) Plnt density, corn (1000 pl/) N pplied to corn (l/) no. of N pplictions to corn N on corn residue in fll (l/) N pplied to soyen (l/) P & K pplictions (l/) 0 40/ /75 Avg. nnul N ppliction (l/) Averge corn yield (u/) Averge soyen yield (u/) Since the strt of this experiment, lrge mounts of crop residue hve een returned to the soil in ll four mngement systems, ut with significnt differences mong them in terms of dry mtter mounts nd composition. Corn returned 75 to 100% more residue thn soyen, ut with much wider C/N rtio. On whole crop rottion sis, verge nnul C return with ove-ground residue incresed in the order CS-rec < CS-int (+8%) < CC-rec (+22%) < CCint (+39%), wheres residue N inputs followed the order CC-rec < CS-rec < CS-int < CC-int. (Fig. 3). Both residue C nd N input were highest in the CC-int system, exceeding the more commonly prcticed CS-rec system y 30 to 40%. Annul residue C, kg C/h/yr () d Residue C Residue N c Annul residue N, kg N/h/yr 3000 CS-rec CS-int CC-rec CC-int Figure 3. Averge nnul cron nd nitrogen input to soil in crop residues ( ). CS = corn/soyen rottion; CC = continuous corn; rec = recommended nutrient mngement; int = intensive nutrient mngement. 70

5 Chnges in Soil Orgnic Cron nd Nitrogen Despite the lrge iomss production in our high yielding corn systems, pek growing seson (out 36 to 55 l C//dy) soil CO 2 efflux ws within typicl rnges for rle crops. In complete 2-yer crop rottion with flux mesurements conducted in corn nd soyen, soil CO 2 efflux (respirtion) in the continuous corn systems ws 22% lrger thn in cornsoyen rottions t oth levels of mngement intensity. Within ech crop rottion, intensified fertility mngement did not cuse significnt increse in soil CO 2 emissions s compred to the recommended prctice. As result, oth SOC nd totl soil N (TSN) incresed in the two CC systems, ut decresed in the CS-rec or remined unchnged in the CS-int system. On verge, SOC declined t n verge rte of 275 l/cre/yr in the CS-rec, wheres it incresed t rte of 565 l N/cre/yr in the CC-intensive (0-12 depth). Similr trends were oserved for TSN (Figure 4). In the intensive continuous corn systems, incorportion of lrge mounts of residue C nd N hs led to significnt uild-up of SOM over just few yers. Although corn yields nd N use efficiency were higher for the intensive corn-soyen rottion, this excellent performnce ws chieved t the cost of exploiting C nd N reserves. Our results here confirm those of recent eddy covrince studies t other sites, showing tht significnt net C losses during the soyen phse of the CS rottion prohiit gins in SOC (Verm et l., 2005; Bker nd Griffiths, 2005). These oservtions led us to conclude tht the N-credit ttriuted to corn-soyen rottions ppers to e due to mining of soil N reserves. Significnt potentil for sequestrtion of tmospheric C therefore exists in intensively mnged continuous corn systems. In the CC-int, 14% more crop residue C ws returned to the soil thn in the CC-rec tretment. Cumultive chnge in SOC, kg C/h () SOC TSN CS-rec CS-int CC-rec CC-int Cumultive chnge in TSN, kg N/h Figure 4. Cumultive chnge in soil cron (SOC) nd soil nitrogen (TSN) fter six yers of tretment. CS = corn/soyen rottion; CC = continuous corn; rec = recommended nutrient mngement; int = intensive nutrient mngement. Soil smples collected in June 2000 nd 2006, 0-12

6 Nitrogen use efficiency Tle 2 presents the overll N lnce nd N use efficiency of the four systems. Without considertion of the chnge in soil TSN sttus, most reserchers would clculte N use efficiency s the totl mount of N in grin / N ppliction rte. One cn see tht this clcultion gives n rtificilly high N use efficiency for the CS-rec system compred to the CS-int or CC systems. It would seem more pproprite to clculte system-level N use efficiency given the mesured loss in TSN nd SOC with soyen in rottion with corn. Tle 2. System level N use efficiency in continuous corn (CC) nd corn/soyen rottion (CS) systems with recommended (-rec) or intensive (-int) mngement ( ). CS-Rec CS-Int CC-Rec CC-Int Annul fertilizer N input, l N/ Annul N removl with grin, l N/ Chnge in totl soil N, 0-12, l N/ Nitrogen use efficiency l N in C+S grin / l N pplied l grin N + chnge in soil N / l N pplied Note tht the dditionl sequestrtion of soil N in the CC systems hs resulted in system-level N use efficiencies tht re more thn doule those determined without soil improvement s considertion. Conversely, the system level N use efficiency for the CS-rec system represented 13% decline (form 3.27 to 2.84) with considertion of soil N loss. Glol Wrming Potentil When fossil fuel consumption, CO 2 -C losses nd trce gs emissions re fctored into totl GWP of these systems, ll four cropping systems were net sources of GHG, with GWP rnging from 0.54 to 1.02 tons of CO 2 -C/cre/yer. Positive or negtive chnges in SOC, intrinsic C costs ssocited with crop production nd soil N 2 O emissions were mjor contriutors to the net GWP. The oxidtion of CH 4 (methne) y these soils gve only smll mitigtion cpcity (Tle 3). Nitrogen fertilizer (16 to 36%), energy used for irrigtion (15 to 22%), electricity for grin drying (13 to 18%), diesel (10 to 16%), nd lime (9 to 13%) were the mjor components of the C costs ssocited with griculturl production. Despite higher C costs ssocited with griculturl production nd lso higher N 2 O emissions, net GWP in the continuous mize systems ws lower thn tht of the corn-soyen systems ecuse sequestrtion of tmospheric CO 2 in SOC ws oserved only in the CC systems. Although the mount of N fertilizer N pplied to corn grown in the intensive cropping systems ws 40% (CC) or 64 to 92% (CS) greter thn the recommended tretments, N 2 O losses were not directly relted to the level of N input only. Significnt N 2 O losses were oserved during the soyen yer especilly fter soyen hrvest.

7 Tle 1. Glol wrming potentil (GWP) expressed s CO 2 -C equivlents for continuous corn nd corn-soyen rottion. Averges for corn nd soyen grown during GWP = Agriculturl production + SOC + soil N 2 O + soil CH 4. A negtive numer indictes sequestrtion of C from the tmosphere. GWP components Continuous Corn Corn-Soyen Recomm. Intensive Recomm. Intensive Tons CO 2 -C equivlents / cre/ yr Agriculturl N fertilizer Production P,K, fertilizer Lime Seed, pesticides Mchinery Diesel Irrigtion Grin drying Totl Soil C Soil N 2 O Soil CH GWP Conclusions At time when there is growing concern out the ility to produce dequte corn to meet demnd for food, feed, nd fuel (Cssmn nd Lisk, 2007), the results from our reserch highlight severl importnt points. First, while corn yield potentil ppers to hve remined reltively stle over the pst 18 yers, there remins lrge gp etween verge corn yields currently chieved y frmers nd the yield potentil ceiling tht cn e exploited through improved crop mngement prctices. Second, intensifiction of cropping does not necessrily increse GHG emissions nd GWP of griculturl systems provided tht crops re grown with est mngement prctices nd ner yield potentil levels, resulting in high resource use efficiency. Therefore, high-yielding continuous corn systems hve significnt potentil for GHG mitigtion, prticulrly if corn grin is converted to ioethnol. Mnging t high yield levels cretes lrge sinks for C nd minerl N, therey providing the prerequisite for sequestering tmospheric CO 2 nd voiding lrge N 2 O emissions tht could result from inefficient utiliztion of soil or fertilizer N. Finlly, the N credit ssocited with corn soyen rottions ppers to e the result of soil N exploittion. Net soil C loss ws recorded for the conventionl corn-soyen rottion. Other studies utilizing eddy covrince techniques confirm tht the totl gross C fixtion (GPP) y corn is twice tht of soyen. Ecosystem respirtion of corn, however, is only 60% of corn GPP ut is 85% of GPP for soyen. Thus the net C sequestrtion potentil of corn is four times s gret s soyen. The gret differences in corn nd soyen C sequestrtion potentil suggest tht continuous corn systems my indeed hold greter promise for mitigtion of glol wrming thn the conventionl corn soyen rottion.

8 References Adviento-Bore, M.A.A., M.L. Hddix, D.L. Binder, D.T. Wlters nd A. Doermnn Soil greenhouse gs fluxes nd glol wrming potentil of high-yielding mize systems. Glol Chnge Biology. 13: Bker, J.M. nd T.J. Griffiths Exmining strtegies to improve the cron lnce of corn/soyen griculture using eddy covrince nd mss lnce techniques. Agriculture nd Forest Meteorology. 128: Cssmn, K.G Ecologicl intensifiction of cerel production systems: Yield potentil, soil qulity, nd precision griculture. Proc. Ntionl Acd. Sci. (USA) 96: Cssmn, K.G., Doermnn, A., Wlters, D.T., Yng, H Meeting cerel demnd while protecting nturl resources nd improving environmentl qulity. Annu. Rev. Environ. Resour. 28: Cssmn K.G. nd Lisk A. J Food nd fuel for ll: Relistic or foolish? Biofuels Bioprod. Biorefin. 1: Duvick, D.N. nd K.G. Cssmn Post-green-revolution trends in yield potentil of temperte mize in the north-centrl United Sttes. Crop Sci. 39: Verm, S.B., A. Doermnn, K. Cssmn, D. Wlters, J. Knops, T. Arkeuer, A. Suyker, G. Bur, B. Amos, H. Yng, D. Ginting, K. Hurd, A. Gitelson, E. Wlter-She Annul cron dioxide exchnge in irrigted nd rinfed mize-sed groecosystems. Agric. nd Forest Meteorology. 131:77-96 Wilde, M Mnchester frmer s record corn yield in question. Wterloo-Cedr Rpids Courier, My Yng, H.S., A. Doermnn, A. Lindquist, D. Wlters, T. Arkeuer, nd K. Cssmn Hyrid-mize mize simultion model tht comines two crop modeling pproches, Field Crops Res. 87: