262 Southern Conservtion Systems Conference, Amrillo TX, June 26-28, 26 CONSERVATION VS CONVENTIONAL TILLAGE,FALL DOUBLE CROPPING AND COVER CROP EFFECTS ON CROP WATER USE IN SUBTROPICAL SOUTH TEXAS Bo Wiedenfeld 1* 1 Texs Agriculturl Experiment Sttion, 2415 E. Highwy 83, Weslco, TX 78596 * Corresponding uthor s e-mil ddress: -wiedenfeld@tmu.edu ABSTRACT Wter for irrigtion is ecoming incresingly restricted, nd production costs continue to rise in sutropicl South Texs. Conservtion tillge offers potentil dvntges in oth res, ut requires effort to implement successfully. A study is currently underwy in the Lower Rio Grnde Vlley to compre conservtion vs conventionl tillge nd to evlute fll doule cropping nd cover crops compred to fll fllow under conservtion tillge. The cropping progrm eing used is cotton / sorghum innul rottion. Soil wter loss is reduced somewht when crop residues re retined on the soil surfce, ut in-seson crop wter use y spring crop is not ffected y tillge method. In the fll, doule cropping nd cover crops withdrw significnt wter from the soil compred to fllow. In single yer, cotton yields were not ffected y tillge method, ut were lower following fll doule crop or cover crop compred to fll fllow. Grin sorghum production showed some improvement due to conservtion tillge compred to conventionl tillge for oth fll fllow nd fll doule crop, ut for n unknown reson, not for fll cover crop. Soil orgnic mtter content hs risen from.8% to 1.17% over 4 yer period, ut shows no ffect due to the cropping tretments pplied. Some wter svings hve een found for conservtion tillge, ut the effects re not gret nd depend on rinfll ptterns. Plnting nd weed control re mjor chllenges, ut sustntil reductions in cost cn e chieved. INTRODUCTION Wter vilility for irrigtion hs ecome mjor concern for South Texs. Conservtion tillge offers the dvntge of reduced field opertions compred to conventionl tillge which should result in lower costs, etter yields nd reduced risk (Rier et l., 24; Smrt & Brdford, 1999). Wter loss is reduced, soil structure improves (Wright & Hons, 25), nd oxidtion of orgnic residues is not s rpid (Slins-Grci et l., 1997) s tillge is reduced. Hopefully this will result more efficient wter use s well s lower costs. No studies, however hve thus fr reported ny wter svings due to reduced tillge, nd Licht & Al-Kisi (25) reported tht soil moisture storge nd crop wter use efficiency were not ffected y tillge system in Iow. Doule cropping nd cover crops offer the potentil to increse orgnic mtter ccumultion improving soil properties, ut will increse initil wter requirements. Plnting nd weed control re mjor chllenges for implementing conservtion tillge. The ojective of this study is to compre conservtion vs conventionl tillge, nd lso to evlute fll doule cropping nd cool seson cover crops compred to fll fllow under conservtion tillge.
Southern Conservtion Systems Conference, Amrillo TX, June 26-28, 26 263 MATERIALS AND METHODS The study is eing conducted in Lower Rio Grnde Vlley of Texs, n re with climte tht is sutropicl (verge dily temperture rnges from high of 84 o F in July to low of 6 o F in Jnury), nd semirid (verge nnul rinfll <24 in.). A innul cotton sorghum rottion is eing grown, nd four cropping tretments re eing pplied: 1) conventionl tillge - fll fllow; 2) conservtion tillge - fll fllow; 3) conservtion tillge - fll doule crop; 4) conservtion tillge - fll cover crop. The doule crops re corn following cotton, nd soyen following sorghum; nd the cover crops re lck ots following cotton, nd hiry vetch following sorghum. Spring crops re eing furrow irrigted s required, nd fll crops re eing grown without irrigtion. Tretments re eing pplied in plots16 rows wide spced 4 in. prt y 15 ft in length, nd re replicted 4 times in rndomized lock design. The study ws initited in the fll of 22 nd is currently in the 4 th spring crop, which will e the completion of the 2-yer rottion for the 2 nd time. Conventionl tillge consists of shredding following crop hrvest, disking severl times, deep chisseling in 2 directions, disking severl times gin, then edding up the lnd. The field is cultivted s required to control ny weeds until the next crop is plnted, nd s the crop is grown. Conservtion tillge ttempts to leve previous crop residues on the soil surfce s long s possile, nd to reduce tillge opertions. Cultivtion is typiclly performed prior to ny furrow irrigtion in order to mintin rised eds to fcilitte furrow irrigtion. Weed control is performed using hericides. Prmeters eing mesured include vrious crop responses, irrigtion requirements nd chnges in soil properties. Dt ws nlyzed sttisticlly using nlysis of vrince nd men comprisons using Duncn s multiple rnge test. RESULTS AND DISCUSSION The primry differences in soil wter use etween the tillge & cropping tretments in this study occurred during the fllow periods due to differences in the cover tht ws left on the soil surfce, nd in the fll due to differences in wter use y the crop eing grown (Fig. 1). Wter use y the spring crops ws ffected only slightly y tillge nd soil cover, cotton using etween 3.6 nd 32.4 inches nd sorghum using etween 17.6 nd 18.5 inches of wter. Wter loss during the fllow periods ws reduced 25% y the retention of crop residue on the surfce. Where no fll crop ws grown, conservtion tillge resulted in n verge 11.5% reduction in wter use compred to conventionl tillge. The fll cover crops used n verge 11.3 inches of dditionl wter, ut over hlf of tht ws recovered through svings from the reduced wter loss due to the surfce residue. Fll doule crops use n dditionl 15 to 24 inches of wter. Only out third of this is recovered y reduced losses due to the crop residues. These differences re reflected in the mount of irrigtion wter required to furrow irrigte the cropping tretments the following spring (Fig. 2). Cotton yields were not significntly ffected y conservtion tillge compred to conventionl when left fllow in the fll, ut oth fll doule cropping nd cover crop reduced cotton yields (Fig. 3). Grin sorghum production showed some improvement due to conservtion tillge compred to conventionl tillge for oth fll fllow nd fll doule crop, ut for n unknown reson, not for fll cover crop (Fig. 4).
264 Southern Conservtion Systems Conference, Amrillo TX, June 26-28, 26 Soil NO 3 - -N levels mesured in Jnury were highest for fll fllow (conservtion nd conventionl tillge) compred to fll doule cropping nd cover crops, which my reflect immoiliztion of soil N y the fll crop (Fig. 5). Soil N vilility hs een reported in other studies to e reduced y plnt dditions in the short term ut enhnced in the long term (Frnzleuers et l., 1995). Orgnic mtter contents rose from.8% t the initition of this study to 1.17% fter 3 yers, ut show no sttisticlly significnt differences due to the tillge tretments pplied. Other studies hve reported increses in orgnic C prticulrly ner the surfce t some point in time under no-till (Frnzlueers et l., 1995; Slins-Grci et l., 1997; Wright & Hons, 25), ut no increse in orgnic mtter levels hve een reported for ny reduced tillge system tht involves t lest some tillge. CONCLUSIONS Conservtion tillge in sutropicl South Texs offers dvntges over conventionl tillge, ut lso poses significnt chllenges. New procedures nd equipment modifictions re required. Plnting nd weed control re difficult, ut dequte yields cn e mintined. Wter svings re errtic depending on rinfll pttern, ut improved soil moisture sttus t ny given time would improve the chnges of mking crop when drought conditions occur. Differences in soil wter sttus so fr hve een due only to crop nd surfce residues, nd not due to ny long term chnges in soil properties. Sustntilly lower costs, however, due to fewer field opertions would e definite enefit of conservtion tillge. REFERENCES Frnzlueers, A.J., F.M. Hons nd D.A. Zuerer. 1995. Soil orgnic cron, microil iomss, nd nitrogen in sorghum. Soil Sci. Soc. Am. J. 59:46-466. Licht, M.A. nd M. Al-Kisi. 25. Corn response, nitrogen uptke, nd wter use in striptillge compred with no-tillgend chisel plow. Agron. J. 97:75-71. Rier, L.A., F.M. Hons nd J.W. Richrdson. 24. An economic comprison etween conventionl nd no-tillge frming systems in Burleson County, Texs. Agron. J. 96:415 424. Slins-Grci, J.R., F.M. Hons nd J.E. Mtoch. 1997. Long-term effects of tillge nd fertiliztion on soil orgnic mtter dynmics. Soil Sci. Soc. Am. J. 61:152-159. Smrt, J.R. nd J.M. Brdford. 1999. Conservtion tillge corn production for semirid, sutropicl environment. Agron. J. 91:116-121. Wright, A.L. nd F.M. Hons. 25. Soil cron nd nitrogen storge in ggregtes from different tillge nd crop regimes. Soil Sci. Soc. Am. J. 69:141-147.
Southern Conservtion Systems Conference, Amrillo TX, June 26-28, 26 265.4 wter use (in./dy).3.2.1. Jn Fe Mr Apr My Jun Jul Aug Sep Oct Nov Dec Jn dte Conventionl, Fll - fllow Con till, Fll - fllow Con till - Fll - ots Con till - Fll - corn Figure 1. Dily crop wter use sed on evpotrnspirtion for the 4 cropping tretments in the cotton corn/ots yer. Furrow Irrigtion 1 8 3 Mr 1 My 6 inches 4 2 conventionl conservtion conservtion conservtion fll fllow fll fllow fll cover crop fll doule crop Figure 2. Amount of irrigtion wter pplied to the 4 cropping tretments on 2 dtes.
266 Southern Conservtion Systems Conference, Amrillo TX, June 26-28, 26 16 14 Cotton Lint Yield 24 12 1 ls/c 8 6 4 2 conventionl fll fllow conservtion fll fllow conservtion fll cover crop conservtion fll doule crop Figure 3. Cotton yields for the 4 cropping tretments. 12 Sorghum Biomss 25 1 stlks & leves heds 8 ls/c 6 Col 2 4 2 conventionl conservtion conservtion conservtion fll fllow fll fllow fll cover crop fll doule crop Figure 4. Grin sorghum stlk, lef nd hed production for the cropping tretment.
Southern Conservtion Systems Conference, Amrillo TX, June 26-28, 26 267 2 Soil NO -N 3 15 ppm 1 5 conventionl conservtion conservtion conservtion fll fllow fll fllow fll cover crop fll doule crop Figure 5. Soil nitrte-n levels for the 4 cropping tretments following the 2 nd full crop yer (cotton corn/ots).