Effect of Stover Mulch on Soil Temperature, Corn Root Weight, and PhosphorusFertilizer Uptake1

J. J. ONDERDONK AND J. W. KETCHEsoN2

ABSTRACT

Bands of corn stover placed on soil in different positions rela-tive to corn (Zea mays L.) rows decreased soil temperature ata 10-cm depth 2.5C for maxima, doubled the proportion of rootgrowth in the surface 5 cm of soil, and tripled fertilizer uptakefrom a surface-applied band of 32P-labeled phosphorus fertilizer.The greatest increase in uptake occurred with the band ofstover on both sides of the row. Total root growth to a depth of15 cm was not greater with stover than without it.

The increase in uptake was credited to the relatively greaterroot growth near the surface, which in turn was believed dueto the temperature depression and a tendency for a morehorizontal direction of root growth. While a more favorablesoil moisture level, as found under mulch, would be necessaryfor root growth and proliferation, it was not considered initiallyresponsible for directing roots closer to the soil surface.

Additional Index Words: soil moisture, corn root direction,no tillage.

MOSCHLER ET AL. (4) suggested from field experimentsin Virginia that surface-applied fertilizer for no-till

corn (Zea mays L.) was more efficiently used than ferti-lizer disced into plowed soil for conventionally plantedcorn. In their experiment, the no-till corn was grown in anonplowed soil with a chemically-killed cover crop. Theconclusions were based on the tendancy for the no-till sys-tem to leave a similar soil test level as conventional tillagealthough yields (and presumably nutrient removal) washigher in the no-tillage. Better moisture retention below themulch was considered responsible for the greater efficiency.

Van Wijk, Larson, and Burrows (7) demonstrated theeffect of different mulch placements on soil temperature.Allmaras and Nelson (1) found that a straw mulch appliedbetween corn rows increased root weight and proliferationin 1 year of higher than normal soil temperature and ma-tric suction, but decreased them in 1 year of lower tem-perature and suction. Mulch applied directly over the cornrow had the reverse effect. Onderdonk and Ketcheson (5)found that a soil temperature of 17C would cause cornroots to grow closer to a horizontal plane than either higheror lower temperatures. The maximum temperature of acyclic regime appeared to produce an effect similar to thattemperature maintained uniformly. If mulch reduces theamount by which maximum temperatures exceed 17C, itshould promote a more horizontal directon of root growthand result in relatively more roots near the soil surface.

1 Contribution from Dep. of Land Resource Science, Univ.of Guelph, Guelph, Ontario. Canada Dep. of Agr. financial as-sistance is gratefully acknowledged. Tagged fertilizer preparedby Tennessee Valley Authority. Received April 10, 1973. Ap-proved June 1, 1973.2 Former graduate assistant now with Ontario Ministry ofEnvironment, and Associate Professor, respectively.

The purpose of the work reported in this paper was todetermine the effect of corn stover mulch on soil tempera-ture, root distribution, and fertilizer P uptake.

MATERIALS AND METHODSPlots were located on a well-drained site, with a 7% slope.

The soil was classified as Guelph loam (Brunisolic Gray BrownLuvisol) (USDA equivalent designation-Typic Hapludalf).The previous crop was no-till corn. A broadcast application ofammonium nitrate (33% N) was applied to all plots at a rateof 112 kg N/ha. A 32p_iabeled fertilizer (22% P, initial spe-cific activity 0.46 me per g P) was broadcast at a rate of 28.8kg P/ha in a 30-cm wide band to one side of each corn row(soil test indicated a low fertilizer P requirement). The differ-ential treatments consisted of the previous year's choppedstover applied in single 30-cm wide bands over the labeled fer-tilizer (SF), the side of the row opposite the labeled fertilizer(F-S), and in double 30-cm wide bands covering both sides ofthe corn row (SF-S). The single and double bands were equiv-alent to 4,500 and 9,000 kg dry stover/ha, respectively. Thecorn row spacing was 76 cm. A check treatment was providedwithout stover (OS). A randomized complete block design wasused with eight replications. Treatment effect F-values werecalculated from an orthogonal, single-degree-of-freedom sub-division of treatment sums of squares.

Grain corn (United hybrid 106) was planted on May 3,1971 in undisturbed soil with a no-till planter at 118,000plants/ha. At the sixth leaf stage, the population was thinnedto 59,000 plants/ha.

Samples consisting of the excess above-ground plants (thin-ning stage), and of the leaf below and opposite the ear (tassel-ling stage) were collected, dried at 70C, weighed, and groundin a Wiley mill. Whole plants were also harvested at the tassel-ling stage to determine dry matter production. The fertilizer Pcontent of the ground plant material was determined by press-ing it into planchets and measuring the radioactivity with anend-window G.M. detector. This activity was compared to theactivity of standards which were prepared by mixing nonactiveplant material with known amounts of 32P-labeled fertilizer.Results were expressed as mg fertilizer P per plant.

Roots from 30-cm squares of soil, situated 5 cm from thebase of the plants, were harvested from the fertilized side ofOS, SF, and SF-S stover treated rows when the plants were atthe tasselling stage. The root samples were taken from threesuccessive 5-cm depth intervals (commencing at the soil sur-face) and at two sites in each replication. The roots were re-moved from the soil using a water floatation procedure similarto that described by Cahoon and Morton (2). Harvested rootswere washed in distilled water, dried at 70C for 72 hours,and weighed.

Soil temperature was determined for each of the three stovertreatments from emergence to fourth leaf, and from sixth totenth leaf stages of growth, using a three-pen continuous tem-perature recorder with sensing bulbs installed at the 10-cmdepth on the fertilized side of the rows. Soil moisture was de-termined, using gypsum blocks at 0-, 3-, 6-, and 9-cm depths forseveral time periods following a typical rainfall event. Sincereplication of temperature or moisture measurements was notpossible due to limited equipment, confidence limits could notbe established for these parameters.

RESULTSThe application of stover to the soil as compared to no

stover did not produce a statistically significant (P = 0.05)

904

ONDERDONK & KETCHESON: EFFECT OF STOVER MULCH 905

iUJ

50

10

5

n

f f

T22 S

ASSETAGE

• V77* 6TH LSTAGE

'///

LLING

- S < = IEAF

- s x = *

'///, '///, y///fOS F-S SF SF-S

STOVER TREATMENT

Fig. 1—Influence of surface-applied stover on surface-appliedfertilizer P uptake at two stages of growth.

effect on corn yield. It did increase the uptake of P ferti-lizer by the plant (Fig. 1). The effects were greater at thetasselling than at the sixth leaf stage. Stover applied to bothsides of the corn row (SF-S) gave the highest uptake ateach stage of growth (statistically significant at P = 0.05).Next in uptake was the single band of stover over the ferti-lizer (SF), followed by the single band opposite the ferti-lizer (F-S). The two latter treatments were significantlydifferent only at the tasselling stage.

The greater fertilizer uptake from the stover treated soilwas associated with more root dry matter in the surface 5cm of soil than was found in the no stover treatment (Fig.2). The largest amount of root in this layer of soil wasfound with the double band of stover (SF-S). At the 5-10cm interval the no stover treatment had the largest rootweight. Weights for the 10-15 cm intervals were similarfor all treatments. The interaction between root weight andsoil depth interval was statistically significant (P = 0.05).Roots harvested from the 0-5 and 5-10 cm depth intervalswith stover cover were large and typical of nodal adventi-tious roots, whereas roots from the no stover treatmentwere typical of fine lateral roots. This difference was notobserved at the 10-15 cm depth.

Soil temperatures recorded from emergence to fourthleaf stage indicated the stover treatment reduced dailymaximum temperatures as much as 2.5C (Fig. 3/4). Mini-mum temperatures were affected less than maximum (Fig.3B). Soil temperature was also depressed during the sixthto tenth leaf stage, with the larger depression again occur-ring in the maximum (Fig. 4). Stover on both sides of therow (SF-S) reduced temperature more than stover on oneside only.

Following a typical rainfall event, the soil moisture fromthe surface to 9 cm was higher for the stover than for theno stover treatments (Table 1). Even with stover, this layerof surface soil ultimately lost its available moisture.

o<nIi-Q_UJO

XCM

UO

IOUJS>-ccQ

OOCC

2.6

2.4

2.0 -

1.8

1.6

1.4

1.2 -

1.0

.6

SAMPLING INTERVAL___ Cm

5-10

10-15

OS SF SF-SSTOVER T R E A T M E N T

Fig. 2—Distribution of corn roots in soil by depth.

DISCUSSION

The distribution and activity of roots near the soil sur-face was estimated by the uptake of 32P-labeled fertilizerand by excavating roots from different soil intervals. Thefertilizer uptake indicated that the SF-S treatment was themost effective, followed by the SF, F-S, and OS treatments.This effect was more pronounced at the tasselling than atthe sixth leaf stage of growth. The above-ground dry mat-ter yields were similar for all treatments and did not ac-count for the differences in P uptake. Root yields in the0-5 cm interval on the other hand did conform with theuptake by the plants. This suggests that the applied ferti-lizer not only remained close to the soil surface, as foundby Triplet! and Van Doren (6), but depended on the con-centration of roots in this region for its uptake.

The greater root yield close to the soil surface with thestover than with the no stover treatments appears to ex-plain the increased uptake of fertilizer P. At tasselling andfor the 0-5 cm depth interval, the SF-S and the SF treat-

Table 1—Available soil moisture, at three depth intervals,following a typical rainfall event"

Time period following rainfall, daysStover treatment

None (OS)

One aide row (SF)

Both sides row (SF-S)

Depthcm036903690369

2 3 4

5057

.533475718635688479

4348462262617720577869

3143430

5454720

497162

5iture, % ——

2731390

4548660

436557

6

..2028270

3640590

355848

Moisture blocks Installed at Indicated depths below fertilizer band.

906 SOIL SCI. SOC. AMER. PROC., VOL. 37, 1973

25

20 -

ot. 15

<K 10UJ

5 20^

15 -

10 -

LEGEND

x—x No S t o v e r Cover

• — • Stover Cover

X\ " "^.-A A />-.\ /vHHx/:/ V-

A- M A X I M U M SOIL T E M P E R A T U R E - 10 cm d e p t h

-t-

x—x-~,•—»-«NV* /Vx_x_x^x/

\ .*••^w-B - M I N I M U M SOIL T E M P E R ATU R E - 10 cm d e p t h

18 20 22 24 26 28 30 I 3 5 7 9M A Y J U N E

1 9 7 1

Fig. 3—Daily maximum (A) and minimum (B) soil tempera-tures, at 10 cm depth below fertilizer band, as affected bystover treatment from emergence to fourth leaf stage ofcorn growth.

ments yielded 2.2 and 1.5 times the OS treatment roots,respectively. By comparison, the uptake of fertilizer P atthe same stage for these treatments was 3.7 and 2.3 timesthe OS treatment, respectively. The apparent enhanced up-take relative to root weight increases might be explainedby more favorable moisture relations in the soil belowthe stover.

Using the maximum temperatures for the OS and SF-Streatments, an estimation of the direction of root growthfrom the temperature-direction relationship developed byOnderdonk and Ketcheson (5) predicts that roots in thelatter environment would grow closer to the surface thanthose in the former environment. The above relationshipwas developed for primary roots, but it is believed thatearly adventitious roots would exhibit a similar behavior(3). The maximum soil temperature for the SF treatmentwas intermediate between the OS and SF-S treatments, andthe root weight and fertilizer uptake were also intermediate.

The F-S treatment decreased soil temperature on the fer-tilized side of the corn row and increased fertilizer uptakerelative to OS, although the effects were smaller than with

30

— 25o

20

20

15

10

-i——i——i——i——rLEGEND

-1———f T

x——x No S t o v e r C o v e r ( O S )• — • S t o v e r One S ide Row (SF)o—a S t o v e r Both S ides Row (SF-S)

*y•?•/X

i?~

.»-1-0

.-»-»'"-V•a\*fam^*^*'\w- ^°-V\ »

^A- $L«No^«4To-»-» \/m

A - M A X I M U M SOIL T E M P E R A T U R E - 1 0 c m d e p t h-H -+- -t- -+- -+- -t- -+- -+- -+- -I-

#&*.x-x/9=8'

^K^\ /.^ ^*./ \*.^ AJ-»\ • Nf N9>«> \f '-J-X-.y a-" • ^m' vV,'5N'^!\\ A*W I/V,i_g

B - M I N I M U M SOIL T E M P E R A T U R E - 10 cm depth

24 26 28 30 2 4 6 8 10 12 14 16 18 20J U N E J U L Y

1 9 7 1Fig. 4—Daily maximum (A) and minimum (B) soil tempera-

tures, at 10 cm depth below fertilizer band, as affected bystover treatments from sixth to tenth leaf stage.

other stover treatments. The stover opposite the fertilizerband appears to have influenced roots on the fertilized sideof the row. It is not known whether this was due to a pos-sible difference in heat conductance from one side of therow to the other, or to a transfer of a temperature-inducedstimulus in the plant itself.