Report to the Southwest Florid Wter Mngement District Effects of Microsprinkler Irrigtion Coverge on Citrus Performnce L. R. Prsons University of Florid Institute of Food nd Agriculturl Sciences Citrus Reserch nd Eduction Center Lke Alfred, Florid 3385 Deliverle 9 Finl Report In Florid, the re covered y the irrigtion system hs mjor effect on citrus fruit production (Koo, 1978; Smjstrl nd Koo, 1984). Are coverge increses s one moves from drip to microsprinkler to overhed irrigtion. Drip, microsprinkler, nd overhed sprinkler irrigtion incresed fruit production y 8%, 2%, nd 72%, respectively, over nonirrigted controls (Koo, 1985). Mny citrus growers hve converted to or instlled microsprinkler systems ecuse these systems provide some frost protection nd cn potentilly reduce wter consumption when properly mnged. Microsprinklers normlly do not cover s much lnd re s higher volume overhed sprinklers. If the re covered is too smll, wter stress cn develop, prticulrly during drought yers. In such yers, most growers increse irrigtion durtion nd/or frequency to reduce stress. However, if the irrigted re is too smll, incresing irrigtion durtion or frequency cn wste wter y driving wter elow the root zone. Since most growers now use microsprinkler systems, it is importnt to determine wht minimum coverge is needed with microsprinklers to provide sufficient wter without significntly reducing production. This could potentilly reduce wter consumption y irrigting only the lnd re needed while optimizing fruit yield. The gol of this project is to determine the effect of size of the irrigted re on citrus fruit yield nd tree performnce.
Deliverle 9. Complete finl report. In this revised report, we hve included dditionl informtion (t no extr chrge to the District) eyond wht ws prt of the deliverle. All the work ws completed efore the deliverle dedline. This dditionl informtion is useful for explining the dt nd for nnul comprison purposes. A test ws set up to determine the effects of different undertree irrigtion spry coverge on tree performnce. Amersweet ornge trees on Swingle citrumelo rootstock were used in this study. Trees were plnted in 1992 in 1 x 2-foot spcing on Cndler fine snd (hyperthermic, uncoted Typic Qurtzipsmments). Microsprinkler emitters were instlled in plnting consisting of four locks contining four tretment plots ech. Tretment plots consisted of three rows with 12 trees in row. All dt were collected from trees in the center row of ech plot. Four irrigtion coverge tretments were estlished. Irrigtion design ws sed on specifictions to provide pproximtely 25, 5, 75, nd % coverge of the totl lnd re in the tretment plots. Actul wetted res were slightly less thn the expected wetting coverge due to interference of trunks, low hnging rnches, weeds, nd system inefficiencies tht re not included in the specifictions provided y the mnufcturers. There is some unvoidle overlp of the microsprinkler spry pttern with the 5 nd % coverges. Results for individul yers re summrized in erlier tsk reports. This report will summrize yields nd conclusions regrding coverge. Yields for 23, 24, 25, nd 26 re shown in Figs. 1 through 4. In these figures, rs with the sme letter on them re not significntly different from ech other t the p<.5 level. There ws no significnt difference etween the 5 nd 75% coverge tretments in 23. The 25% tretment ws significntly lower thn the other three tretments. In these 3 tretments, yields were ove 4 oxes/cre. In the 25% 2
coverge tretment, yield ws elow 3 oxes/cre nd significntly lower thn the other 3 tretments. Three hurricnes pssed ner this grove in 24. Hence, yields were quite low during this seson ecuse fruit ws lown off the trees. Becuse of high yield vriility, there ws no significnt difference mong ll four tretments t the.5 level. The hurricne proly contriuted to the yield vriility. Yields were etter in 25, nd there ws no significnt difference etween the 25, 75, nd % tretments. We do not know why fruit production in the 25% tretment ws etter in 25 thn in 24, ut reduced crop in one yer cn sometimes lternte with lrger crop in the following yer. The hurricne effect ws proly still influencing the trees nd their fruit production in 25. In 26, there ws no difference etween the 5, 75, nd % tretments, ut the 25% tretment ws significntly lower thn the other three tretments. Fig. 4 most clerly shows the trend tht ppers in the previous yers. In most of the yers, yields on the 5, 75 nd % coverge tretments were higher thn the 25% tretment. Usully, there ws no significnt difference etween the 5, 75, nd % tretments. These results show tht 25% coverge is not dequte for optimum yield, ut tht there is no dvntge to hving 75 or % coverge. Bsed on the results of this study, it is recommended tht t lest 5% of the totl lnd re e covered when using microsprinklers. 3
6 5 Yer 23-4 Yield (Boxes/cre) 4 3 2 c 25% 5% 75% % Irrigtion Coverge (%) Fig. 1. Fruit yield in 23. Brs with the sme letter re not significntly different (p<.5). Yield (Boxes/cre) 6 5 4 3 2 Yer 24-5 25% 5% 75% % Irrigtion Coverge (%) Fig. 2. Fruit yield in 24. Brs with the sme letter re not significntly different (p<.5). 4
6 5 Yer 25-6 Yield (Boxes/cre) 4 3 2 25% 5% 75% % Irrigtion Coverge (%) Fig. 3. Fruit yield in 25. Brs with the sme letter re not significntly different (p<.5). Yield (Boxes/cre) 6 5 4 3 2 Yer 26-7 25% 5% 75% % Irrigtion Coverge (%) Fig. 4. Fruit yield in 26. Brs with the sme letter re not significntly different (p<.5). 5