Crop Rotations, Reduced Tillage and N Fertilization Effects on Corn Yields And Aflatoxin Levels

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1 Crop Rottions, Redued Tillge nd N Fertiliztion Effets on Corn Yields And Afltoxin Levels J.E. Mtoh nd M. Rihrdson Texs AgriLife Reserh nd Extension Center Stte Hwy Corpus Christi, TX 78- jmtoh@g.tmu.edu Introdution The physil nd iologil environments of soils (Brer nd Mtoh. 99; Mtoh, et l. ; Wright, et l. ) n e influened y tillge nd rop rottions. The hnge in these environments my e ssoited with the quntity nd distriution of orgni mtter, n importnt onstituent of soils (Mtoh, et l. 999). Response to N fertiliztion nd rop produtivity n e funtion of some of these ioti nd ioti hnges. The purpose of this study is to determine the influene of tillge intensity nd rop rottion on grin produtivity nd fltoxin level in orn t vrying levels of N fertiliztion. Mterils nd Methods The experimentl site ws Vitori ly (montmorilloniti Udi Pellusterts), vertisol with t lest inhes of drk gry surfe soil. Predominte ly in this soil is swelling nd shrinking montmorillonite. The site ws loted t the Texs AgriLife Reserh nd Extension Center t Corpus Christi, nd hd een ropped to grin sorghum nd otton on lternte twoyer yles nd low N rtes for the previous three yers. Initilly, the soil tested low to medium in ville N nd P nd high in ville K. Four rop rottion shemes using the two si row rops (orn nd otton) grown in the region nd soyen s the min loks while two tillge systems (minimum, MT, nd onventionl tillge, CT) were ompred in split-plot within eh min lok. Minimum tillge involved four tillge opertions with less thn -inh plow depth while CT hd eight opertions with plow depth t -inhes. Eh tillge tretment within eh ropping system ws split into three su-plots whih reeived,, nd l N/. Nitrogen rtes for the soyen rop were,, nd l/. Phosphorus ws lnketed to ll plots t l P O /. All tretments were ompred in four replitions. A medium mturity orn hyrid nd n erly mturing otton ultivr were used in the study. Soyen vriety RA (Group IV) ws seeded in lternte yers to omplete the rottion sheme. Results In the first yer, devstting drought stressed the orn nd otton resulting in negligile grin yields, therefore yields re not reported for yer one of the study. Results for the seond yer when norml rinfll ws reeived re presented in Figures nd. The rottion effets from otton or soyen on grin yields were onsiderly greter thn in Yer. Without N fertiliztion, orn yields under MT inresed pproximtely l/ (7%) when orn followed otton s ompred to monoulture orn whih produed totl yield of only 9 l/. With CT, the rottion inresed yields pproximtely l/ or % ompred to ontinuous orn. As N rte ws inresed to l/, the net ontriution from the rottion

2 deresed to 7 nd %, respetively, for MT nd CT systems. The rottion effet from soyen under oth tillge systems ws generlly less thn with otton (Fig. ). Without N fertiliztion, the soyen ontriution rnged disppointing 7% to 8% for the MT nd CT systems, respetively. With N fertiliztion, the rottion effet deresed to nd % for MT nd CT, respetively. The lesser ontriution from soyen thn otton to the rottion effet in Yer my e prtly ttriuted to the drought stressed soyen rop hving restrited N fixtion pilities in the Yer seson. The effet from rop rottion ws slightly entuted when orn ws grown with MT ompred to CT. Corn: Corn Cotton:Corn Grin (l/ x ) 7 Coventionl Till d d..9 N Rte (l/) Fig.. Corn grin yields s influened y otton rottion, N rte nd tillge in Yer. Brs highlighted with the sme letter re not signifintly different ross tillge systems, Fisher s LSD.. Corn: Corn Soyen:Corn Grin (l/ x ) 7 Conventionl Till N Rte (l/) Fig.. Corn grin yields s influened y soyen rottion, N rte nd tillge in Yer. (Soyen reeived,,lsn/) Soil moisture ws ove verge strting the growing seson in Yer ut negligile

3 rinfll throughout the growing seson used severe plnt stress for moisture nd finl grin yields were pproximtely -% of Yer yields. In Yer, orn ws grown under seprte tretments, six of whih were in monoulture of ontinuous orn ropping system nd six in otton-orn rottion. The rottion sheme for this yer did not inlude soyen. In the third seson, very smll differenes in tretment response were mesured due to drought relted normlly low yields. In generl, orn grin yields rnged from high 9 with l/ to low l/ with CT (Fig. ). Averges over fertilizer tretments within ropping systems show little or no yield differene due to tillge. However, under CT response to N fertilizer ws signifint for ontinuous orn nd the otton-orn systems, response to N ws reorded only up to l/ for oth ropping systems. The slight derese in yields from the otton-orn rottion ompred to ontinuous orn ws possily due to lower residul soil moisture in the soil profile t seson strt when otton preeded orn. These dt show tht under identil fertiliztion regimes nd CT, orn following otton in droughty seson will produe slight inrese in grin ompred to ontinuous orn. No enefit from rottion ws evident under MT. Conventionl Till Corn:Corn Cotton:Corn Grin (l/ x ).99 d d d N Rte (l/) Fig.. Corn grin yields s influened y otton rottion, N rte nd tillge in Yer. Grin yields during the fourth yer of the study inresed sustntilly over those for Yer nd were out 9% of those yields for Yer (Fig. ). The rottion enefit from otton ws onsiderly elow tht mesured in Yer nd rnged from % for MT without N fertiliztion to % for the CT system. Unlike the findings during Yer, the rottion effet in Yer ppered to inrese slightly with N fertiliztion in oth tillge systems, however the yield effet ws nonsignifint. Highest yields were mesured when orn ws grown with the MT system t the high N rte.

4 Corn:Corn Cotton:Corn Grin (l/ x ) Conventionl Till d...9 d.9. N Rte (l/) Fig.. Corn grin yields s influened y otton rottion, N rte nd tillge in Yer. Sustituting soyen for otton in the Yer rottion improved orn grin yields onsiderly over ontinuous orn when N fertiliztion ws withheld (Fig. ). The pproximte l/ inrese (8%) in grin due to soyen for the MT system deresed to 7 l/ (8% inrese) for orn grown with CT, ut still equled or exeeded the soyen enefit mesured erlier in the Yer seson. Using soyen in the rottion rther thn otton produed signifintly higher orn yields s ompred to the otton rottion only when N fertilizer ws exluded (Figs. -). The enefits of the soyen rottion were gretest in the MT system t zero N. Corn:Corn Soyen:Corn Grin (l/ x ) Conventionl Till N Rte (l/) Fig.. Corn grin yields s influened y soyen rottion, N rte nd tillge in Yer. (Soyen reeived,,ln/)

5 Afltoxin levels in orn grin vried widely with sesons. When preipittion ws verge nd ove (Yers nd ), disese levels were generlly elow or slightly ove the ritil pp with n verge of nd pp for Yers nd, respetively. In these two sesons, tretment differenes were reltively smll ut trended lower for the MT system when orn followed otton. Corn stressed for moisture (Yer ) ontined pproximtely fold inrese in fltoxin ompred to non-stressed orn with n verge of pp s ompred to in sesons when soil moisture ws dequte. Corn following otton produed higher disese levels s ompred to monoulture orn in oth tillge systems. Redued tillge ppered to slightly lower grin fltoxin. Tle. Influene of rop rottion/tillge nd fertilizer N rte on fltoxin levels in orn grin Cropping System ) Tillge Fertilizer N Afltoxin (pp) L/A Yer Yer Yer Continuous orn CT Continuous orn CT 9 98 Continuous orn CT 8 8 X Continuous orn MT Continuous orn MT 7 9 Continuous orn MT 88 X 9 Cotton:orn CT 8 Cotton:orn CT 8 Cotton:orn CT 9 X 8 Cotton:orn MT 78 Cotton:orn MT 8 Cotton:orn MT X 7 CT = onventionl tillge; MT = minimum tillge Summry nd Conlusion Results showed tht preipittion nd ville soil moisture will gretly influene response of orn to rop rottion nd tillge tretments. With dequte preipittion nd no N fertiliztion in the seond study yer orn following otton produed 7% higher yields while orn following soyens produed 7% yield inrese. However, in the fourth yer of the study, the ontriution from soyen rottion ws onsiderly greter thn from the otton rottion, espeilly t N rtes. These dt suggest the enefiil effets from soyen rottion with orn on soil qulity nd yields my hve greter temporl dependeny thn with the otton rottion. Although the tillge intensity effet ppered smller thn in the se of the rottion effet on orn yields, the positive effets from oth otton nd soyen rottions were usully est expressed in the MT system. Corn following otton produed higher grin fltoxin ompred to monoulture orn while reduing tillge somewht suppressed disese levels. More reserh is needed to study the possile intertive effets.

6 Referenes Brer, K.L. nd J.E. Mtoh, 99. Rottionl ropping sequene nd fertiliztion effets on soil miroil popultions. Int. Sorghum Millets Newsletter, Vol., p.. Mtoh, J.E., T.L. Provin, nd S.G. Vek, 999. Soil hemil properties s influened y tillge intensities. Annul Meetings of Amerin Soiety of Agronomy, Crop Siene Soiety, nd Soil Siene Soiety of Ameri. Slt Lke City, Uth. Novemer 999. Agronomy Astrts, p.. Mtoh, J.E., C.F. Chilutt, M.P. Rihrdson, nd S.G. Vek,. Impt of otton rottion nd tillge intensity t vrying phosphorus fertility on ertin sorghum insets nd grin yields. Proeedings of th Annul Conservtion Tillge Conferene for Sustinle Agriulture, p Auurn, Alm. Wrights, A.L., F.M. Hons, nd J.E. Mtoh,. Tillge impts on miroil iomss nd soil ron nd nitrogen dynmis of orn nd otton rottions. Applied Soil Eology, p. 8-9.