Efficacy of Boom Systems in Limiting Runoff on Center Pivots

Efficcy of Boom Systems in Limiting Runoff on Center Pivots Authors: Prossie Nkwuk, Ph.D. CGIAR (Consortium of Interntionl Agriculturl Reserch) Ethiopi P.Nkwuk@cgir.org R.Troy Peters, P.E., Ph.D. Wshington Stte University Irrigted Agriculture Reserch nd Extension Center, Prosser, WA. troy_peters@wsu.edu Romulus O. Okwny, Ph.D. Interntionl Wter Mngement Institute Ktmndu, Nepl r.okwny@cgir.org Hossein S. Sdeghi, M.S. Wshington Stte University Irrigted Agriculture Reserch nd Extension Center, Prosser, WA. s.hossein.sdeghi@wsu.edu Abstrct. Center pivot nd liner move irrigtion systems design nd opertion re primrily limited by soil infiltrtion rtes. Boom systems hve been suggested to improve infiltrtion nd decrese runoff by reducing the instntneous wter ppliction rte of center pivots nd liner move systems. In this reserch project, we compred runoff from plots irrigted with typicl in line sprinklers on liner move irrigtion system with those irrigted with off set boom systems. In line drops consistently generted greter runoff thn the boom systems in ll of the irrigtion events. Differences in runoff between the drop types were significntly different for the second, third, fourth nd fifth irrigtion events. The runoff differences from in line drops rnged from 3% to 24% greter thn the boom systems. Runoff s percentge of irrigtion wter pplied incresed with ech irrigtion event on both drop types. Keywords. Center Pivot, Irrigtion, Sprinklers, Offset, Boombck, Appliction Rte 1

Introduction The use of mechnized sprinkler irrigtion systems, prticulrly center pivots nd liner move systems (or liners) hve rpidly incresed in the United Sttes. Severl surfce irrigted res re being grdully converted to sprinkler irrigtion, especilly center pivots. In 2007, center pivot nd liner move irrigtion systems ccounted for 25 million cres (10.5 million h) or 46% of the totl re (56.8 million cres) irrigted in the United Sttes (USDA, 2010). The growth in mechnized sprinkler irrigtion systems, prticulrly center pivots in the recent yers my be due to the utomtion built into them tht llows for irrigtion of mny types of crops with miniml lbor input, lrge re coverge, bility to operte on reltively rough topogrphy, nd finlly, these systems cn be highly efficient nd uniform when they re designed nd mnged properly (Wilmes et l., 1993; Kincid, 2005). However, the efficiency nd uniformity of these systems cn be considerbly reduced by potentil runoff s result of the high ppliction rtes tht re inherent with moving sprinkler systems (Kincid et l., 1969; Thooymni et l., 1987; Kincid, 2005; Luz, 2011). Wter ppliction rtes in moving sprinkler irrigtion systems re generlly much higher thn those of sttionry sprinkler systems. This is becuse moving systems must pply wter over given point in the field in limited mount of time. When the ppliction rte exceeds both the soil infiltrtion rte nd the soil surfce storge, wter will flow on the soil surfce producing runoff (Mielke et l., 1992; Luz nd Heermnn, 2004). Potentil runoff continues to be the mjor problem ssocited with moving sprinkler systems (Kincid, 2005). Surfce runoff is prticulrly more severe in center pivots or liners operted t low pressures (Wilmes et l., 1993; Thooymni et l., 1986). The problem worsens t the outer end of the lterl for center pivots where the ppliction rte is much higher thn the other points closer to the pivot center (Allen, 1990; Kincid et l., 1997; Bjorneberg, 2003; Bjorneberg et l., 2003; Smith nd North, 2009). Potentil runoff cn be reduced by incresing the lterl speed on the center pivot or the liner move systems, thereby reducing the irrigtion depth pplied during ech irrigtion run. This however cn be detrimentl for plnts needing deeper depths of irrigtion. The mjor chllenge in the design nd opertion of center pivots nd liners then becomes designing systems tht pply sufficient wter to meets plnts wter requirements with no or miniml surfce runoff. The design should therefore be ble to limit wter ppliction rtes to vlues tht re less thn the sum of the soil s infiltrtion rte nd the surfce storge cpcity t ll times nd long ll points on the lterls (Allen, 1990). The infiltrtion rte vries with the soil type nd the soil moisture conditions. Surfce storge temporrily llows the wter to pond until it infiltrtes completely. Soil surfce storge cpcity is the bility of soil to hold prticulr depth of wter ponding on its surfce depressions without letting it flow. Soil surfce storge cpcity depends on the field slope, soil surfce conditions nd the type of crop grown on tht field. Runoff cn be prevented or reduced by incresing the mount of soil surfce storge (Neibling et l., 2009). Another wy of trying to reduce runoff potentil is by reducing the wter ppliction rte while mintining n irrigtion depth pproprite for the needs of the plnts. Booms (offset booms, or boombcks) re one wy of decresing the wter ppliction rte. In boom systems, the sprinkler heds re offset 10 20 ft (3 to 6 meters) from the irrigtion tower s frme (Figure 1). Booms lower wter ppliction rte by pplying wter to lrger re (tht is, by incresing the sprinkler wetted re) 2

thereby llowing the soil to bsorb the wter t slower rte, thus llowing lrger ppliction depths. This llows for less frequent irrigtions nd thus reducing surfce evportion nd lso reduces diseses in some crops (Kincid et l., 2000). Less frequent irrigtions of more wter per pss lso result in deeper root zones, less wer nd ter on the pivot s motors nd ger boxes, nd power svings. Booms on lternte sides of the center pivot or liner move system cn reduce the ppliction rte of lowpressure spry sprinklers (King nd Kincid, 1997). The objective of this work ws to compre runoff from booms with typicl in line drops tht hve the sprinkler heds in line nd directly underneth the irrigtion tower s frme. Mterils nd Methods The reserch ws conducted t the Wshington Stte University (WSU) Irrigted Agriculture Reserch nd Extension Center (IAREC) locted ner Prosser, Wshington (ltitude 46 15 N, longitude 119 44 W), USA. A liner move irrigtion system, Vlley 8000 Series model, 148 m long ws used for this experiment. Originlly the system hd ll of its drops directly underneth the tower frme. The system ws modified to include lternting booms in two groups s shown in Figure 2. The drops for the booms were moved 15 ft (4.6 m) from the irrigtion tower s frme using light weight glvnized steel tubing (BoomBcks mde by IACO, Vncouver, WA). All the drops cross the liner move system (both in line nd booms) were locted pproximtely 9 ft (3 m) prt long the tower frme nd 5 ft (1.5 m) bove the soil surfce. The sprinkler type used on both booms nd in line drops included Nelson S3000 spinner with yellow plte (Nelson Irrigtion Corportion, Wll Wll, Wshington, USA), sprinkler nozzle dimeter of 11/64ths (4.37 mm; Nelson nozzle size # 22) nd Nelson 15 psi (103 kp) pressure regultor to give n ppliction rte of 3.2 gpm (12.2 L min 1 ). A pond nerby the experimentl field ws the source of wter. The pond received surfce wter diverted from the Ykim River. Figure 1. A prt of the liner move system fitted with booms for the sprinkler runoff tests in 2013. 3

The experimentl field ws formerly whet field. After the whet ws mowed, the field ws plowed with disk plow. The runoff re plots were prepred mnully using shovel nd rke towrds the end of the month of September 2013. The field contins Wrden silt lom soil with verge snd, silt nd cly of 21, 68 nd 11% respectively nd with slope of bout 0.5%. Twelve runoff plots were instlled in three row by four column rrngement s shown in Figure 2. Averge distnce between the plots in column rnged between 16 nd 25 ft (5 to 7.5 m). There were two plot loctions under regulr drops nd two loctions under booms in ech row. The plot loctions were such tht when the liner move system ws directly over the plots, ech plot ws mid wy between two djcent drops on the irrigtion tower frme. Before the runoff plots were demrcted by metl frmes, the res where the plots were to be locted underwent some preprtions. First, the loctions were rked bck nd forth to remove whet strw tht ws covering the field surfce fter the field ws plowed. The res were then dug up with shovel; the soil ws dug up nd turned over. This ws to help loosen up the subsoil nd to lso brek up clods of the erth. The plot res were then rked bck nd forth gin to further remove ny strw tht might hve been remining on the surfce nd to lso mke sure tht ll the plots were t the sme slope nd soil surfce condition. This helped to minimize the vribility between the plots infiltrtion nd soil surfce storge components of the infiltrtion storgerunoff process. All irrigtion pplictions for this experiment were on reltively smooth nd bre soil conditions. Metl steel frmes of re 12 ft 2 (1.12 m 2 ) were used to cpture representtive smple field runoff nd to prevent plot run on from the surrounding res. The metl frmes were 1/8 inch (3 mm) thick nd 8 in (20.2 cm) wide. The frmes were oriented verticlly nd their bottom edges driven into the ground to depth of bout 3.5 in (9.5 cm). A PVC pipe, 2 inches (5.1 cm) in dimeter nd 5 inches (12 cm) long ws fitted through hole on the down slope outlet end of the frme (Figure 3). The crcks were seled by using duck tpe to widen the pipe just so tht it hd pressure fit. The PVC pipe routed the runoff into cler plstic bg tightly tied on to the PVC pipe. A hole ws dug into the soil ner the outlet of the plot for the bg to sit when collecting runoff from the plot. The volume of the runoff tht collected in the bg ws mesured using grduted cylinder, nd the depth of runoff nd percent runoff (tht is, depth of runoff / depth of irrigtion pplied 100) ws determined for ech plot. Five irrigtions were pplied to the runoff plots with irrigtion intervls vrying between 1 to 4 dys during the month of October. The dtes tht the experiment ws run nd the ppliction depths re recorded in Tble 1. The one dy irrigtion intervl didn t let the soil profile drin sufficiently before irrigtions. The ppliction depths were hence progressively decresed s the experiment progressed to prevent excessive runoff. Appliction depths for prticulr irrigtion events were chosen to ensure tht mesurble runoff occurred on the plots for ech irrigtion event. Rinfll ws miniml during the experimentl period; less thn 0.04 inches (1 mm) of rinfll ws received on 10/8/2013. Ech runoff plot hd two ctch cns plced on the ground ner the plot tht were used to mesure the volume of wter pplied (Figure 3). A block design with two blocks, two tretments nd three replictions per tretment ws used for this experiment nd solved using Minitb 16.2.3 GLM procedure (Minitb, 2012). Tukey s Studentized rnge test ws used for tretment men comprisons of runoff nd runoff percentge t 0.05 probbility level. 4

Figure 2. Runoff plot lyout for field studies in 2013. Figure 3. Runoff plot components. Results nd Discussion Runoff from irrigtion events ws determined during the month of October of 2013. The irrigtion events, including dtes, ppliction depths nd runoff re summrized in Tble 1. Runoff from the in line drops rnged between 11.2% nd 60.1% of the irrigtion depth pplied during the period of testing (Figure 4). The booms generted runoff rnging between 6.9% nd 39.5% of the irrigtion depth pplied. In line (control) drops generted greter runoff thn the booms in ll the irrigtion events; the runoff differences between in line drops nd the booms rnged from 3% to 24% of the irrigtion depth pplied. 5

The differences in runoff from in line drops nd booms were significnt for 2 nd, 3 rd, 4 th nd 5 th irrigtion events. On field level, this reduction in runoff through using booms will minimize crop wter stress by llowing more wter to infiltrte into the soil nd be used by the crop. This will boost crop yields nd lso improve the efficiency of the irrigtion system. Also, with less runoff nd more infiltrtion, pumping costs re reduced since less psses of the center pivot or liner move system will be required to sufficiently irrigte the crop during the growing seson. A boost in crop yields increses frm revenue while reduction in pumping costs reduces crop production costs. Increse frm revenue nd svings in wter nd pumping costs due to booms my be more thn enough to compenste for the incresed equipment costs due purchse, instlltion nd mngement of booms. Tble 1. Dte, wind speed, nd verge irrigtion nd runoff for ech irrigtion event nd for ech drop type. Irrigtion Wind Appliction Runoff (in) ANOVA Difference in Event Dte speed (mph) depth (in) Control Booms probbility runoff** (%) 1 10/2/2013 3.13 1.25 0.13 * 0.09 0.28 3.0 2 10/9/2013 2.71 0.70 0.26 0.20 b 0.03 7.9 3 10/14/2013 3.60 0.61 0.25 0.16 b 0.00 14.6 4 10/16/2013 3.13 0.40 0.25 0.16 b 0.02 22.4 5 10/18/2013 3.20 0.41 0.24 0.14 b 0.02 24.2 Totl 3.37 1.14 0.76 b 0.003 * Vlues in rows with the sme letters re not significntly different t significnce level of 5%. ** Difference in runoff between in line drops nd booms expressed s percentge of irrigtion pplied per irrigtion event. The runoff trends (Figure 4) for both the in line drops nd the booms show similrity in runoff ptterns s ffected by the ntecedent soil moisture content, time between irrigtion events nd soil surfce seling. The soil surfce lyer in both tretments ws eqully dried by evportion nd infiltrtion differences my hve been lrgely influenced by soil surfce seling which ws s result of droplet impct on to the bre soil. This could explin the incresing percent runoff in both tretments s the number of irrigtions incresed (Figure 4). Runoff percentges generlly incresed with incresed number of irrigtions in both tretments. However, the increse ws steeper with in line drops thn with booms. This suggests tht boom systems my preserve the soil structure nd reduce soil compction. Booms thus my be wy of minimizing the increse of runoff tht might occur throughout the seson for in row crops like pottoes. Four out of the five irrigtion events produced significntly different runoff percentges between the regulr drops nd the booms. The first irrigtion event produced the lest runoff for both regulr drops nd the booms due to miniml surfce seling s the plots hd just been estblished nd lso becuse the runoff plots soil moisture content ws lowest prior to the first irrigtion event. As the initil soil wter content increses, infiltrtion decreses. The ppliction intervls for this experiment rnged between 1 to 4 dys. Not llowing the soil profile to sufficiently drin before n irrigtion event further increses the occurrence of runoff. 6

70 60 Control Booms Percent Runoff (%) 50 40 30 20 10 b b b b 0 1 2 3 4 5 Irrigtion Event Figure 4. Runoff percentge (tht is, mesured runoff expressed s percentge of mesured pplied wter) for the runoff tests for ech irrigtion event. Tretments with the sme letter for prticulr irrigtion event re not significntly t significnce level of 5%. Conclusions This study compred runoff from in line drops with boom systems. The highest runoff occurred with in line drops in ll the irrigtion events. In line drops produced between 3% to 24% more runoff thn the booms. This study shows how the use of boom systems is n effective wy of lowering the wter ppliction rte through incresing the wetted sprinkler re thus minimizing soil compction nd encourging infiltrtion of wter into the soil. It ppers tht the more difficult it is to get wter into the soil, the greter the benefit is from using booms. Runoff from prticulr re in field depends on the slope, the initil soil wter content nd the roughness of the soil surfce. In the ppliction of mechnized sprinkler systems, cre must be tken to mtch wter ppliction rtes to infiltrtion rtes of the soil under sprinkler conditions, nd to the soil surfce conditions in order to minimize runoff. Minimizing runoff will result in wter svings, svings in pumping costs nd minimize crop wter stress. Acknowledgements We would like to cknowledge the coopertion of IACO who donted the booms, Nelson irrigtion who donted the sprinkler heds, nd Vlmont irrigtion who helped dvise the reserchers. 7

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