DIVISION

rekE P 0 P T

Evaluation of Dryland Corn and Grain Sorghum Production

In the Southern Plains Using Computer Simulation

This Research Report, RMN SORGHUM IS THE TRADITIONAL SUMMER GRAIN

crop under dryland conditions in the Southern High Plains. However,

97-4, is contributed by the there has been a growing interest in recent years in dryland corn.

D 1 2There has been very limited research in recent years in the Texas

High Plains with dryland corn, so there is a lack of current

Auriculture experimental data to share with producers. Jones and Thaxton 1950 conducted

dryland vanetal tests for corn and grain sorghum at Lubbock, Texas, from 1942-48.

Institute The years of 1945, 1946 and 1948 were extremely dry. Therefore, very little yield

data were recorded for all varieties of diyland corn and grain sorghum. For one corn

>1 West Texas A&l University, hybrid, the average yield over eight years was 1,040 pounds per acre with the highest

yield 2,300 pounds per acre in 1942. For grain sorghum, the average yield was 1,450

Canyon, Texas, and the pounds per acre with the highest yield 2,450 pounds per acre in 1942. Annual

precipitation totaled 27.3 inches in 1942 compared to the avearge of 18.8 inches. A

Texas Agricultural Experiment Station, long-term dryland crop rotation study was conducted in Dalhart, Texas, from

1908-38. Mathews and Barnes 1940 reported 30-year average yields of 1,070

The Texas A&M University System pounds per acre for dryland corn and 2,100 pounds per aae for grain sorghum

grown under a fallow system. In the same study, the average corn and grain sorghum

Agricultural Research and Extension yields for three different methods of cultivation on continuously cropped land were

800 and 1,230 pounds per acre, respectively. Average annual precipitation for the

Center. Anarillo, Texas. 31-year study was 17.5 inches; it is worthy to recall that this period included the

severe drought period of the 1930s. Dryland corn yields ranged Irom 0 in 1933 and

Financial support for the study 1934 when the annual precipitation was only about 10 inches to 3,650 pounds per

acre in 1915 when the annual precipitation was 21 inches. Mathews and Barnes

was provided by the 1940 further reported that corn was more productive at Daihart, Texas, than at most

of the other southern dryland field stations. They concluded that corn was an

Texas Grain Sorghum Board and important dryland crop at higher elevations where summers were cooler, and the

date of the first killing frost was earlier than in Dalhart.

the Texas Corn Producers Board.

Computer Simulation StudyBecause weather is extremely variable, it will require several years of field data

before sound recommendations can be made based on studies using new varieties of

corn and grain sorghum. Modern hybrids and improved cultural practices have

greatly improved the yield potential of both crops, even under dzland conditions.

Computer simulation crop models are available that can analyze soil-crop-climate

interactions. This study used the Erosion Productivity Impact Calculator l-l'IC to

simulate corn and grain sorghum production for 50 years so that the two crops could

be compared for years of widely varying climatic conditions. The results will provide

A klest Texas A&IVI growers information that may be useful during the period that additional field studies

Ware being conducted. Field results for grain sorghum from Bushland, Texas, Stewart

U N 1 V E R S I T `` and Steiner, 1990 and for corn from Akron, Cob., Nielsen, 1995 were used to

validate that the model simulated yields were realistic.

AGRICULTURE

A Memb of The Texas MM Uriwersity System

Simulations were made for five Iocations-Dimmitt, Texas; Bushland, Texas;

Boise City, Okia.; Tribune, Kan.; and Akron, Colo.-ranging from south to north in

the Southern High Plains. Climatic characteristics for the different locations are

presented in Table I. Although all five locations are predominantly summer rainfall

areas, there are some distinct differences in the distribution patterns.

Table 1. Average elevation E, monthly and annual precipitation, and growing

season days GSD for study locations

E Precipitation GSD

Location Feet J F M A M J J A S 0 N I T Days

Inches

Dimmitt, Texas 3,850 0.27 0.37 0.80 1.04 3.13 2.45 1.94 2.67 2.78 2.08 0.73 0.42 18.68 201

Bushland, Texas 4,000 0.51 0.51 0.78 1.01 2.67 3.00 2.69 2.81 1.93 1.53 0.73 0.58 18.74 205

Boise City, OkIa. 4,170 0.44 0.66 0.95 1.55 2.73 2.90 2.82 2.57 1.92 1.81 0.86 0.58 19.79 184

Tribune, Kan. 3,600 0.21 0.42 0.84 1.56 2.54 2.65 2.43 2.02 1.43 0.92 0.48 045 15.96 164

Akron, Cob. 4,580 0.30 0.35 0.83 1.69 3.00 2.48 2.72 1.97 1.22 0.91 0.55 0.43 16.50 143

Moving from south to north, less precipitaion occurs in late summer and early

fall. This can be clearly seen in Figure I J.T. Musick, USLA-ARS, Bushland, Texas,

personal communication that shows 15-day precipitation totals by three-day periods

for selected locations in the southern and central Great Plains. The southern-most

locations have a definite two-peak precipitation pattern, but the second peak becomes

clearly less pronounced for locations further north.

Planting dates used in the model for corn ranged from April 10 in the south to

May 10 in the north compared to grain sorghum planting dates ofJune I in the south

toJune 10 in the north. The dominant soil type for each area was used in the model,

and it was assumed for each year that the plant available soil water storage onjan. I

was 50 percent of maximum. This assumption was made because it is generally

accepted that dryland corn should not even be considered unless there is substantial

stored soil water at the time of planting.

ResultsAverage yields and range of yields for the 50 simulated years are presented in

Table 2. Average grain sorghum yields were higher for the southern locations while

average corn yields were higher for the northern locations. As discussed earlier,

rainfall distribution varies from south to north, and this is believed to be a major

reason for sorghum doing better in the south and corn better in the north.

Distribution of rainfall for various locations shown in Figure 1 illustrates that the

southern locations have a bi-modal distribution of precipitation while the northern

locations have a single-modal distribution. Since grain sorghum is seeded later, it

benefits from increased soil water storage from early rainfall, and late rainfall often

occurs during the heading and grain filling periods. In the northern locations, early

seeded corn receives most of the rainfall prior to maturing while early seeded corn in

the south does not benefit from late precipitation events. Also, temperatures are

cooler in the northern locations. Cooler temperatures are favorable for corn while

unfavorable for grain sorghum.

The 50 years of simulated yields represented a wide range of precipitation

amounts during the growing season. There is a direct relationship between seasonal

water use precipitation during the growing season plus stored soil water minus runoff

and drainage and grain yields. Although yields for any one year can fall above or

Figure 1. Average 15-day Precipitation Moving Totalsby Three-day Periods, January Through December, byMusick of the USDA Conservation and ProductionLaboratory, Bushland, Texas personal communication,1996

J F M A M J.J A $

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below the lines shown in Figure 2

because of the tunelineness of a

particular rainfall event, overall

relationships are represented by the

lines. These relationships indicate that

for grain sorghum, about six inches of

seasonal evapotranspiration are required

before any grain is produced, and for

each inch of additional water used,

about 350 pounds of grain are produced.

For corn, the relationship illustrated in

Figure 2 suggests that no corn grain is

produced unless at least eight inches of

evapotranspiration occurs, but for every

inch of additional evapotranspiration,

there are about 450 pounds of corn

grain produced. The point that the two

lines cross is about 17 inches with a

yield of approximately 4,000 pounds per

acre. This suggests that grain sorghum

would generally yield more than corn

when seasonal evapotranspiration is less

than 17 inches, and corn would yield

more when seasonal evapotranspiration

is more than 17 inches. Average

growing season rainfall for the locations

used in the study is about 10 to Ii

inches. This means that for years of

avenge precipitation, about six to seven

inches of soil water must be available to

meet the 17 inches needed for corn to

yield as much as grain sorghum. This

supports the recommendation that

dryland corn should generally not be

considered unless there is substantial soil

water stored at time of seeding. Even

then, corn yields are not likely to exceed

grain sorghum yields unless growing season precipitation is above avenge.

The findings of this study clearly suggest that there is more risk, particularly in

dry years, associated with corn at all locations studied. In general, grain sorghum

yields were less than 2,000 pounds per acre only about one year out of nine while

corn yields were less than 2,000 pounds per acre about one year out of three except

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Table 2. Average Yields of Corn and Grain Sorghum for Five Locations in theSouthern High Plains for 50 Years of Varying Climatic Conditions

Location Corn Range Sorghum Range Corn/Sorghum

Pounds Per Acre Pounds Per Acre Ratio

Dimmitt, Texas 3,150 630-7,020 3,780 1,620-6,390 0.88

Bushland, Texas 2,340 450-4,860 2,610 990-4,860 0.89

Boise City. OkIa. 2,610 540-5,940 3,060 1,170-5,400 0.85

Tribune. Kan. 3,690 1,080-6,210 3,420 1.710-5,130 1.07

Akron, Cob. 3,060 810-5,400 2,610 1,260-3,870 1.17

Figure 2. Generalized RelationshipBetween Corn and Grain Sorghum Yieldsas a Function of Seasonal Water Use inthe Texas High Plains

10000

8000

6000

4000

2000

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for Tribune, Kan., where yields nearly always exceeded 2,000 pounds per acre for

both crops. Even at Tribune, however, grain sorghum yielded more than corn in the

driest years. For all locations, corn produced more grain than grain sorghum for the

years when growing season precipitation was very high.

The study suggests that long-term average grain yields

of corn will be about 87 percent of those of grain sorghum in

the south portions of the Southern High Plains but will be

about 112 percent of those of grain sorghum in the northern

locations. However, there is clearly more risk with corn

during dry years. On the basis of yield alone, grain sorghum

would be the logical crop of choice for producers in the

south, and corn would be the preferred crop in the north.

However, profit is the goal of the producer, and profit is a

function of yield, production costs and price of the product

Corn prices are often significandy higher than grain

sorghum, particularly for early produced corn. This study

considered only yield; economics will require additional

analysis. We conclude that dryland corn should not be

considered unless there is substantial stored soil water at

time of seeding, and even then, corn yields will likely not be

significantly higher than grain sorghum unless growing

season precipitation is above average. However, corn yields

can be signigicantly higher than grain sorghum in years of

high precipitation. Growers that have high amounts of soil

water stored at seeding time may very well want to plant some dryland corn, but it

may be prudent to plant at least part of their land to grain sorghum in the event that

growing season rainfall is below average.

-Mvsammad Add Ak.bar, WTAMU

-BA. Stewart, WTAMU

-CD. Salisbuiy, TAES

.2

0 4 8 12 16 20 24 28

Seasonal Evapotransplratlon inches

ReferencesJones, D.L and E.L. ThaxtonJr.

1950. Dry-land yields of grain sorghum

and corn at lubbOCk, 1941-48. Progress

Report 1229. Texas Agricultural

Experiment Station, College Station,

Texas.

Mathews, O,lt and B.F. Barnes.

1940. Dryland crops at Dalhart, Texas,

Field Station. USDA Circular No. 564,

Washington, DC.

Nielsen, D.C. 1995. Water

use/yield relationships for Central Great

Plains Crops. Conservation Tillage Fact

Sheet 2-95. USDA ARS, Akron, Cob.

Stewart, BA. andJ.L Steiner.

1990. Water use efficiency. P. 151-173.

In: Dryland Agriculture: Strategies for

Sustainability. Advances Soil Science,

Volume 13, Springer-Verlag, New

York.

Detath ofthe stady are reported in a

thesis submitted in partialfi4iJinent of

requ zrnrtentsfor a Master ofScience is

Agricatare degree, West Texas A&M

Uniuersity, 1996.