DIVISION S-6—SOIL AND WATER MANAGEMENTAND CONSERVATION

Wheat Response to Different Soil Water-Aeration Conditions1

M. G. ANAYA AND L. H. SiOLZY2

ABSTRACTA graphical yield surface was constructed for wheat (Tri-

ticum aestivum L.) grown on Yolo silt loam with 13 differentsoil water-aeration combinations. The experiment was conductedin a growth chamber under controlled environmental conditions.Oxygen over the soil surface was maintained at different per-cent O2 concentrations from 0.9 to 21%. Various soil waterregimes were obtained by irrigation at different soil suctionsfrom 8 to 99 centibars (cbars). The highest grain yields wereobtained in two treatments, one of 9.6% O2 watered at a soilsuction of 15 cbars, and another treatment of 4.3% watered at

8 cbars. The lowest production was in the treatment of 0.9% O2watered at 99 cbars, and the difference between the highestand lowest yields was 347%. From the data, the regressionequation for grain yield was: Y = 15.94 — 0.1324 X] + 3.1813X2 — 0.1297 X2

2, where Y = grain yield in g/pot, X1 = soilsuction in cbars, and X2 — percent O2. The maximum predictedyield calculated from the equation is at a level of 12.0% of O2

irrigated at a soil suction of 8 cbars. However, the maximumproduction recorded was obtained at 9.6% O2.

There was a high correlation coefficient (0.94) between waterconsumption and grain production. An inverse relationship ex-isted between grain yield and protein content. The highest levelof grain protein content (22.6%) was obtained in the lowestproducing treatment, while the lowest level of grain proteincontent (16.5% ) occurred in the highest producing treatment.The difference in grain protein content between treatmentswas 37%.

Additional Index Words: response surface, soil aeration, soilwater, excess soil oxygen.

486 SOIL SCI. SOC. AMER. PROC., VOL. 36, 1972

WHEAT (Triticum aestivum L.) is the source of almost20% of the total necessary calories for the world's

population. It is cultivated on about 231 million ha everyyear, and is the staple food in 43 countries (12).

Wheat growth is affected by many factors including soilwater stress and soil oxygen. Plant species have differentoxygen requirements, and several environmental factorsaffect plant respiration (5, 16). Some of these factors areavailable oxygen, light, temperature, and nutrient availa-bility (2, 10, 13, 17). Wheat plants show more growthwhen irrigated at low rather than high soil suction (6, 11).

Campbell et al. (4) conducted growth chamber experi-ments to study the effects of soil water stress and oxygendiffusion rate on seed set and wheat yield. In their study,treatments where soils were irrigated at lower soil suctionvalues showed yield increases of 80% over the control.However, where soil aeration conditions were improved,wheat yield increased by 230% over the control. Higherwheat yield was obtained more by improving soil aerationthan by improving soil water conditions. Varade et al. (17)studied the effect of two O2 levels on wheat growth androot porosity: low O2 (0.7 ppm) reduced shoot and rootgrowth, volume of roots, and number of tillers when com-pared to high O2 (7 ppm) conditions.

Day and Intalap (6) studied the effects of four differentsoil water regimes on wheat growth under field conditions.They applied from 90-110 cm of water and found that soilwater stress at any growth stage decreased grain yield.Studies by Martinez (11) showed the effects of 13 differ-ent soil water regimes on the yield of 'INIA' (Mexicansemidwarf) wheat in which he applied 38 to 57 cm ofwater with 5 N levels. Maximum grain yield was obtainedeither when pre-flowering irrigations were applied after80% of available soil water had been used, or when post-flowering irrigations were applied after 90% of availablesoil water had been used. Maximum yield for fertilizertreatment was 120 kg/ha of N.

The purpose of this experiment was to estimate a wheatproduction function for soil oxygen and soil water undercontrolled environmental conditions.

MATERIALS AND METHODSYolo silt loam treated with 0.2% Krilium was packed in

plexiglass cylinders (13 cm diameter, and 47 cm high), 42 cmof the cylinder was occupied by soil. The soil had a bulk den-sity of 1.2 g cm~8 with each pot containing 6.8 kg (air dryweight) of soil. The 5 cm above the soil allowed space for

DESIGN OF TREATMENTS

Double square arrangement

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.9

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99 53 28 15 8Soli suction - 'cb

Fig. 1 — Design of treatments for soil water-aeration conditions.

irrigation water and gas flow for different oxygen treatments.Nitrogen at 150 ppm (soil basis) and P at 100 ppm were pre-viously added to the soil as ammonium nitrate and ammoniumphosphate. The amount of water applied at each irrigationrewetted the soil to a water content of 24.4% by volume, thiswas equivalent to occupying 53% of the total pore space.Tensiometers were installed at 15- and*J6-cm depths to obtaindaily soil suction readings. The suction values at 15 cm wereused to determine when to irrigate the five different soil watertreatments. Suction values at 36 cm were used to observe ver-tical water movement and to avoid excess water at the cylinderbottoms.

Four seeds of TNIA' wheat were planted in each cylinder.After emergence the seedlings were thinned to give two uni-form plants in each container.

The experimental design was replicated twice. For the de-sign of treatments a partial factorial in double square arrange-ment was used, choosing 13 treatments which are indicatedby X in Fig. 1.

Different soil oxygen treatments were achieved by flowinga mixture of air and N in given proportions above the soil sur-face. The different percent O2 over the soil surface changesthe oxygen diffusion rate (ODR) of the soil columns similarto that previously reported by Stolzy et al. (15). Plants weregrown under these conditions during the whole 140-day growthcycle. Mean day length during the first 70 days was 9 hours;during the second 70 days, it was 11 hours. During the first70 days temperatures were 18C (day) and 15C (night); dur-ing the last 70 days it was 24C (day) and 20C (night). Rela-tive humidity was maintained at 65% and the maximum lightintensity was approximately 4,500 ft-c.

Wheat plants were harvested and separated into grains,stems, leaves, and roots. All samples were prepared for analysisby grinding in a Wiley mill. Nitrogen was determined by themicro-Kjeldahl method and crude protein was estimated bymultiplying the percent of N by a factor of 5.27 (12).

RESULTS AND DISCUSSIONData on plant responses to the 13 different soil water-

aeration treatments are presented in Table 1.

Table 1—Effects of 13 soil water stress-aeration combinations on wheat responsesSoil

sucttoncbars

8289915538

289915538

2899

Plant response

0.90.90.92.02.04.34.34.39.69.6

21.021.021.0

Grain

15.30 d*12.60d6.88

2. 28 be13.42d30.64 a26.63 ab11.65d30. 75 a26. 18 abo22. 57 be21.77 c14.87d

Leaves

10.4 de9, 5ef8. 5f

10.3 de11.2 cd14.3 a13. 5 ab10. 5 de13. 5 ab12. 3 bo11.8 od11.4cd11.0 cde

Stemsg/pot —————————

17. Od17.3 d12.0 e23. 4 be14. Ode29.0 a26. 5 ab13. Oe24. Ob20. 5 od21.5o25. 1 ab21.0c

Roots

0 641.063.072.461.273.002.922.443.283.191.822.311.52

Proteinmg/pot3,443 d2. 507 e1,562 f4, 144 c2,456 e5, 086 ab4,740b2, 144 ef5,474 a4, 294 bo3,859 cd3,810od2, 810 de

Water useI/pot22.200I6.12de12.15e29.00b16.30d34. 76 a32.97 a13.36 de34. 25 a25. 27 bo27.24b27.48b14.30de

GrainsNo. /pot

521 d345 e158 f540 d319 e843 a811 ab299 e811 ab714 bo722 be678 d349 e

RatioStraw/grain

1.86 be2.05b2.98 a1.51 de1.88 be1.41 del.SOde2.06b1.22e1.26e1.49 de1.68cd2. 15 b

" Any two values within a column are significantly different at the 5% level If they have no letters In common.

ANAYA AND STOLZY: WHEAT RESPONSE TO SOIL WATER-AERATION CONDITIONS 487

Grain Yield

Grain yield was significantly affected by the differenttreatments applied (Table 1). The maximum differencesbetween lowest and highest production was 347%. In thetreatment where the soil was watered at a suction of 99cbars and O2 at the surface was 0.9%, grain productionwas 6.88 g/pot. On the other hand, when soil was wateredat a suction of 15 cbars and O2 at the soil surface was9.6%, grain yield was 30.75 g/pot.

The multiple regression analysis showed linear effectsof soil suction, and both linear and quadratic effects dueto different O2 treatments for wheat growth (Table 2).Calculated values for yield of wheat from the regressionequation are presented graphically in Fig. 2. This graphshows the response surface of grain yield to different soiltreatments.

The optimum grain yield calculated by taking the firstpartial derivative from the regression equation was ob-tained when the soil was watered at a suction 8 cbars andwhen O2 over the soil surface is 12.0%. However, thehighest yield measured was obtained in the treatment with9.6% O2. No interaction effect between soil suction andsoil O2 was found for grain production. This means thatthe response of grain production to changes in soil suctionis the same at each level of O2; the lines on the responsesurface are parallels (Fig. 2).

A comparison of grain yields obtained with differenttreatments showed that the highest level of O2 (21%)reduced production while the lowest O2 treatment (0.9%)drastically reduced grain production.

Quality and Plant ProductionLarger differences due to treatments were obtained in

grain yield, number of grains, protein produced, and waterused (Table 1). Smaller differences were obtained in stem,leaf, and root growth. Nevertheless, the same linear effectsof soil water and the quadratic effects of soil O2 werefound for these plant responses (Table 2). The exceptionto this was in root growth where only soil O2 produced aquadratic effect, and soil water treatments produced noeffect.

Protein production was closely related to grain yield;however, protein content was inversely related to grainproduction. The lowest and highest protein contents ob-tained were 16.5% and 22.6%, respectively. When ahigh production of grain is obtained with the same N con-tent in the soil, a dilution of this nutrient occurs in thegrain, causing lower protein content or lower quality. Oneway to get an increase in protein content is to apply ade-

Fig. 2—Calculated response surface of wheat growing under13 different soil water-aeration treatments.

quate quantities of N while maintaining optimum condi-tions for wheat growth (14).

The straw: grain ratio showed higher values as soilwater stress was increased. Root growth was affected prin-cipally by oxygen treatments, showing a quadratic effect.The highest oxygen treatment (21% O2) caused a reduc-tion in root growth while the lowest oxygen treatment(0.9% O2) increased with an increase in the suction valueat which the plants were watered. This difference couldbe attributed to better soil oxygen condition for wheatwhen soil was watered at 99 cbars, rather than at 8 cbars.Wheat developed additional secondary roots under thelowest oxygen treatment.

Water Use

The effects of both soil water and soil oxygen treatmentson water use can in some cases be related to a smallerplant and so less leaf area for transpiration (Table 1). Themost water was used by plants under optimum soil aerationconditions and decreased considerably in both the low O2and high soil suction treatments. Weekly water use datafor the 9.6% O2 treatment watered at 15 and 53 cbarssuction is presented graphically in Fig. 3. Weekly water usedata for these treatments shows that approximately 16%of total water needed was- used in the first 10 weeks and

Table 2—Regression equations for wheat responses grown under different soil water stress-aeration conditions

Plant responseGrainWater useStrawRatio strawigrainGrainsLeavesProteinRoot

Unitg/pot1/potg/pot

No. /potg/potmg/potg/pot

Correlationcoefficient*

H0.96*0.92*0.87*0,96*0.95*0.89*0.96*

YYYYYYY

0.90* Y

Regression equation= 15. 9378-0. 1324 X, + 3. 1813 X2 - 0. 1287 X,2= 23. 9392 - 0. 1743 X, + 2. 3942 X, - 0 0988 x|= 33.18 - 0.252 X1 + 1.824 Xj + 0.084 Xj -0. 079X|+0= 2.05 - 0.173 X2+ 0.008 Xf +0.07 X§= 484.697 - 4.5277 X^ 81. 6157 Xj - 3.2133 X§= 10.1719- 0. 02 X,+ 0.7224 Xz -0.0297 X| .= 3, 248. 55 - 22. 8315 X, + 444. 3411 Xj - 18. 3138 X|= 1.2965+0.3747 X^ - 0.0165X|

0571 X! X,

" Probability level 5%. ' Probability level 1%, X1 - soil suction in cbars. % - percent oxygen over soil surface.

488 SOIL SCI. SOC. AMER. PROC., VOL. 36, 1972

TIME - WEEKS

Fig. 3—Weekly water use by wheat when the soil was irrigatedat suction values of 15 and 53 cbars, and O? treatmentof 9.6%.

84% in the last 10 weeks. Similar results were obtainedfor the 0.9% O2 treatment under different water regimes(Fig. 4). The average water use for treatments in thefirst 10 weeks was 27% and 73% for the last 10 weeks.The highest water use occurred between the 13th and 15thweeks during the grain filling stage. Differences in wateruse by plants in the various treatments started about 50days after planting. Under field conditions, Erie et al.(7) found that 15% of the total water use by wheatoccurred before early root stage and 85% was used tocomplete the growth cycle.

Water efficiency expressed as liters of water used pergram of grain produced showed the lowest efficiency(1.76) in the treatment watered at a suction of 99 cbarswith 0.9% O2. The highest efficiency (1.11) was obtainedin the treatment with the highest grain yield. Water effi-ciency for grain production was increased as O2 and waterconditions were optimum.

Plant Response to Excess O2 Conditions

Several of the measured plant responses showed a highproduction of grain, leaves, stems, and roots as the percentO2 was increased. However, in the 21% O2 treatmentsproduction was generally less. The regression equationsfor these data were quadratics (Table 2). Anderson andKemper (1) studied the effects of aggregation stabilityon corn growth and found reduced yields at high aggre-gate stability levels. They suggested the possibility that anover supply of oxygen caused a reduced corn yield. AfterWarburg's discovery in 1920 (18) in which high concen-trations of O2 inhibited the rate of photosynthetic O2 evo-lution in the unicellular alga Chlorella, it was confirmedby other workers that normal air (approximately 21%O2) has a marked inhibitory effect on photosynthesis (3).According to Gerschman (8) after Priestly discovered O2in 1775, he wondered if "pure air" would not exhaust theanimal's powers too soon. Also according to Gerschman(8), Bert (1878) established experimentally the cardinalfeatures of "O2 poisoning" for both animal and plantsystems. The toxic effects of high O2 supply in soil toroots have been suggested but not too well-documented.In sandy soils where water films around roots could be

< 2

•—• 8cbCs--A 28 Cbo—O 99 cb

«£&*4 8 12 16

TIME - WEEKS

Fig. 4—Weekly water use by wheat when the soil was irrigatedat suction values of 15 and 53 cbars, and O2 treatmentof 0.9%.

thin, very high oxygen diffusion rates to respiration sueswould be possible causing O2 toxicity.

The "luxury consumption" of oxygen has been suggestedin which carbohydrate would be used by roots in respira-tion and thus reduce the amount for plant growth (1). Acalculation based on the wheat grain yield data in thispaper was made by Luxmoore et al. (9). They indicatedthat a 9% increase in yield would result if during the grainfilling stage all root respired assimilate went into grain (9).

Excess O2 supply to root could have at least one of twoeffects on plant production: (i) O2 toxicity or (ii) luxuryconsumption of photosynthesis.

HARRIS: INFILTRATION RATE AS AFFECTED BY SOIL FREEZING 489