Sweet corn can be grown in
Alaska's cool environments by employing
clear polyethylene mulch to
raise soil temperatures.
Rows should be run north and
south, spaced about 5 feet apart for
4-foot wide mulch.
Weeds can be controlled under
clear polyethylene mulch by spraying
with atrazine after seeding and
before mulching

Dinkel, D. H.

English

ScholarWorks@UA

GROWING SWEETCORN in A laska'scoolenvironmentsD. H. DINKEL Horticulturist LIFE SCIENCES LIBRARY Goldrnine sweeet corngrown on a mulche d plot at Matanuska, Alaska, was r eady for har vest in late A ugust of 1964. University of AlaskaALASKA AGRICULTURAL EXPERIMENT STATION Bulletin 39 November 1966 SUMMARY Sweet corn can be grown in Alaska's cool environments by em-ploying clear polyethylene mulch to rai se soil temperatures. Rows should be run north and south , spaced about 5 fee t apart fo r 4-foot wide mulch . W eeds can be controlled under clear polyethylene mulch by spraying with atrazine after seeding and before mulching. ADVANTAGES OF CLEAR MULCH • • • • • H igher soil temperatures. Faster and better germination . Moisture conservation through reducing evaporation . Extensi~ of the growing season at the seedling end of the growth cycle. Spring frosts are not as critical where plants are covered with polyethylene mulch . Accelerated growth and early maturat ion. GROWING SWEET CORN IN ALASKA F E\iV gardeners in Alaska have succeeded in growing sweet corn , although many have tried . Cool soil and air temperatures, rather than an insuff icient frost-free period, have been suggested as the reason warm season crops such as corn are not adapted to this environment. Low soil temperature is probably the most critical factor limiting the growth of sweet corn in mo t areas of A laska. A minimum soi l temperature of 50 • F has been generally accepted ior germination and gro\\·th of corn. Average temperature at a two-inch soi l depth is seldom much above jQ •F in Alaska's Matanuska Valley. Compa ri sons oi clea r, black and smoke polyethylene mulch, black pet t-ole um mulch, b lack pape r a nd combinations of ome of these ma-te ri als shO\Yed that only clear poly-ethylene raises soil temperatures suff iciently to produce sweet corn consistently in south central A laska . During the past decade several cold to'erant sweet corn varieties have been developed. T he availability of these improved varieties has contrib-uted to the successful production of sweet corn in Alaska. CLEAR POLYETHYLENE MULCH Clear mulch ha several incidental advan tages. I t fosters faster and more complete germination of corn seed which emerges in t ime to take advantage of the long clays during the solstice. T he young seed li ngs under plastic are protected from light spring frosts, so that earlier planting is possible. By conservi ng moisture in the surface soil, roots are enabled to grow nea rer the surface, taking advantage of a warmer environment. Short-wave solar radiation is read ily transmitted by clear poly-ethylene to the soil underneath thus rais ing its temperaturit The warm soil radiates at a longet- wave length which clear polyethylene does not transmit as readily. );! oisture vapor often present on the polyethylene also absorbs long-wave length ener -gy radiated from the soil. Clear polyethy lene thus retards heat loss from th e soil. T he trapped heat is not dissipated by wind nor by the evaporation of soil moisture, which is greatl y reduced by clear polyeth y-lene mulch . Greatest ri ses in soil temperature under clear polyethylene occur dur-ing sunny periods. F igure 1 shows the effect of solar radiation on soil temperature at the two-inch depth under clear polyeth ylene as com-80 r----.~a-----------.-------------~----~ ~ 60~--~--~~----------~--------------~~----~ ·-I 0 if.l s oil 50~------------------~--------------~----~ 100 Dark da ys 400 I n c ide nt r adiation 700 Sunny da y Figure I.-Relation between total. daily incident radi•ation (Langleys, measured by an Epply pyranomete•r) and soil temperature of mulched and unmulched plots (•average o·f daily minimum and maximum two inches belo·w the surface) for 24 days in June 1964. Left extreme represents cloudy days, r ight extreme sunny days. pa red to uncovered ad jacent plots during June 1964. Lines show the relati onshi p between dail y averages of the maxm1l!m and 1111111111um tem 1~eratures and the amount of in-cident radiation accumulated du ring that day. Accumulated daily radia-tion ( Langelys per day) for the month of June 1964 varied from a low of 122 on a dull, cloudy day to 758 for a clear, sunny day. Little d i iference existed between the soil tem perature in covered and uncov-ered plots on dull, cloudy days, 11·hereas great differences developed du ring clea r, sunny days. O n sunny clays soil temperature differences of :30oF or greater were found under cl ear mulch as compared to unmul-ched plots . Soil temperatures under black polyethylene mulch resemble those found in unmulched soil. In studies at Matanuska during 1%2 and19G3, marketabl e ears were obtained when sweet corn \\·as grown through clear polyethylene but not when grown through bl ack polyethy-lene or without polyethylene covers. Table 1 presents details on elate of planting. date of first harvest and yield per foot of row for two var ie-ties g ro1rn through -b-foot wide clear polyethylene. No corn was produ-ced in any yea r by any varieties not mulched with clea r p~1 l yethylen e . Under clear polyethyl ene mulch , -b to Table 2. - Response of Eadiking sweet corn. in terms of. average height attained, to width of clear pl-astic mulch. Matanuska. Alaska, 1965. Mulch width None 3 feet 4 feet 5 feet Height attained by -J u ly 20 Aug 10 Inches 10 21 27 41 34 53 29 46 10 times more eed germinated than in unmulched plots. Plants mulched with clear polyethylene g rew as .much as three times the height of unmulched corn. T he common thickness o£ poly-ethylene film for mulch is 0.0015 inches ( L 5 mil ) . Data collected during 1965 on the effect of width of mulch is presented in Table 2. Maximum height wa.obtainecl with -1-foot wide clear polyethylene, 1rhich was a better response than obtained \l'ith a :3-foot st rip. A strip 3-(eet wide was no better than the -±-foot width. The same sort of a response to 8- and -±-foot polyethylene was fou nd in 20 other varieties tested in 1065. To insu re iest harvest best success and ea rl-weet corn should be planted on the T·able I.-Planting d a te, first h a r v est d a te, and y ie ld of marketable ears per foot of row for two adapted sweet corn varieties, Matanusk a, Alaska. 1962 through 1965. earliest ground as soon as it can be properly pre-pared and work-ed in the spring. Good sites are gentle snuth-fac-First Ears per Varietr Plan ted harvest foot Goldmine June 6, 1962 Sept 6 Go1dmine May 10, 1963 A ug 26 1.3 Goldmine May 12. 1964 Aug 25 1.5 VH-631 Mav 14, 1965 Aug 30 0.9 Figure 2.-Above, sweetcorn plots •at Matanuska in 1964 after planting and mulching. Below, same plots several weeks later. Note poor stand a nd growth of unmulched plot at far left. ing slopes away from trees and buil dings that might shade the plant-ing. The necessary fertilizer should be applied (2 112 pounds/] 00 square feet of 8-32-16 or its equivalent) , worked into the soil , and the surface prepared into a flat. fine seedbed. A flat seedbed without clods makes it easier to apply film mulch. Poly-ethylene covers retard evaporation of so il moisture so the seedbed can be left in a fl uffy condition without foste ring excess moisture loss. It is recommended that corn be seeded about J 1/2 inches deep in one- to t\\'o-seed hill s, one foot apart in the rows. Rows should run north and south. They should be spaced far enough apa rt so they can be conveniently covered without inter-fering with the polyethylene cover-ing of adjacent rows. Five to 6-foot wide row spacings are needed for "!-foot width polyethylene. Figure 2 shows a planting of sweet corn just after the mulch was applied by hand, together with the same planting several weeks after the corn had been let out from the polyethylene. APPLYING POLYETHYLENE MULCH Polyethylene mulch can be applied by hand (or with mulch laying ma-chines on large areas). P lastic mulch must be securely anchored around all edges with soil so that it is not blown off . Where winds are prevalent during the spring, as in the l\1atanuska Valley, special care is needed. Dig a trench 4 to 6 inches deep parallel to the seeded row so that when the polyethylene sheet is centered over the row about 6 inches will overlap into the trench. l~oll out the polyethylene and anchor one side first by filling the trench. Repeat the operation on the other side, stretching the polyethylene tight across the row. E nds should also be trenched in and covered. Mulch laying machines are towed by a t ractor. T hey dig trenches on both sides of a seeded row, roll the plastic out. and press its edges into the trench . Shovels or disks then cover the edges. When the seedlings are 3 to 4 inches high. slit the polyethylene directly over them and gently pulE the leaves up through the li t. The plants will tlt .t by themselves emerge th rough holes in clear polyethylene. WEED CONTROL Weed growth U!lifr a clear polyethylene cover may seem to present a problem. If the edges of the polyethylene mulch are securely anchored it has not been necessary to eliminate the weeds. W eeds under the mulch have not produced viable seed to reinfes t the soil. Not much plant food and water is act-ually lost to weed growth confined under the polyethylene. A nnual weeds can be controlled by spraying the seeded row with atrazine herbicide at the rate of 1 teaspoon (75 per cen t atrazine) per gallon of water ( 3/4 pound of active ingredient per acre). A gallon should cover 500 square feet. The spray is applied before the mulch. This rate has given excellent season-long weed control under mulch , with no harm to the corn. It is not suffi-cient to control weeds in unmulchecl soil. \ Varm moist conditi ons under the mulch create a better condition for weed control. W eeds can be controlled on the expoc;td soil be-hveen rows and arm:nd the edges of the polyethylene by ~praying with P remerge ( DNBP) at the rate of 5 pounds per acre. Spray before pull-ing the corn through the mulch but after weeds have germinated . Atrazine applied at higher rates remains in the soil so thi s herbicide should not be used if it is intended to grow some crop other than corn on the treatw plot in the following year. POLL! NATION Adequate pollination is needed fo r good. well-filled ears. Best natural pollination is ach ieved when corn is planted in several short rows rather than one long row. If corn is planted in one long row, then pollen from tassels should frequently be shaken over the developing silks. V ARieTIES The earli est vari eti es available a re suggested for Alaska. Goldmine sweet co rn has, under mulch, con-sistentl y produced ears comparable to those obtained in southern envir-onments. Other good varieti es of which seed is now available are Earliking, Spancross, Sunglow and Golden GIOl. The earliest va ri eti es in these tests were t\\·o seedlings, one from an Alaskan breeding pro-gram, the other (VH-631) from a breeding program Vineland , O ntario. conducted at Seed of these new va rieti es should be availabl e in a few years. _"\t Matanuska no ~weet corn va ri eti es produced ears un less grown under clear polyethy-lene mulch. Black polyethylene excludes visible light and for this reason restricts weed g:·owth under it. Exclusion of visible light also makes it possible to mechanize thi s mulch smce machines a re now availabl e \\·hich burn a hole in the plastic and plant a seed through it. Light passing through the hole phototropically guides the growing seedling through it. thus eliminating the hand labor of releasing the plant from the mulch. Black polyethylene. however. does not tran mit heat rays to the soil and so is undesirable fo r corn pro-ducti on in .r\ Iaska. O n the other hand, clear poly-ethylene transmits and traps solar heat but does not suppress weed growth . Both black and clear polyeth ylene retard moisture loss . 2 Sprea d 4-ft pLastic, cente r e d on row, fo ld back 6 i nc hes . 1 4 Fo ld down film o n o n e si d e , an c ho r by fi ll ing t n-.1 nc h with ~o i 1. G 3 Fold plastic back on other s ide , dig shallow trenches. 5 On ot he r s ide, pull film taut, anchor ~ in s ame way. Anch o r both e nd s in sa me way. As we e d s and co rn g row, they pu s h pla s ti c mul c h up. : ;:_y·· '~··~0f:~~~;:·~::(t 7 Wh e n co rn i s 3 to 4 inches tall, s lit t he mu 1 c h . Ge 11 t l y p u ll 1 e a v e s through . . ';·:;~st;~z:w~~~~!.,:,·} Figure 4.-Steps in planting and mulching corn. Figure 3.-Mulched corn plot at Matanuska in 1965, a cooler than aver·age season. Note how weeds under mulch have pushed the plastic up. Vigorous weed growth under the plastic did not .reduce the corn's response to mulch. :FUTURE DEVELOPMENTS plasti c. It would trap heat, conserve .-\ polyethylen e cover that would transmit radiation in the infra- red Tegio•J of the spectrum while exclud-ing visible light would combine the a dvantages of both clea r and black moisture, control weeds, and seedlings through pre-cut thus allowing mechanization. a material may be availabl e fe,,· years . guide holes Such m a 

Growing Sweetcorn in Alaska's Cool Environments

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Growing Sweetcorn in Alaska's Cool Environments

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