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Published online 5 June 2006
Published in Agron J 98:992-998 (2006)
DOI: 10.2134/agronj2005.0356
© 2006 American Society of Agronomy
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Forages

Forage Yield Response to Water Use for Dryland Corn, Millet, and Triticale in the Central Great Plains

David C. Nielsen*, Merle F. Vigil and Joseph G. Benjamin

USDA-ARS, Central Great Plains Research Station, 40335 County Road GG, Akron, CO 80720

* Corresponding author (david.nielsen{at}ars.usda.gov)

Received for publication December 27, 2005.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Forages, with greater water use efficiency (WUE) than grain and seed crops, could be used to diversify reduced and no-till dryland cropping systems from the traditional wheat (Triticum aestivum L.)–fallow system in the semiarid central Great Plains. However, farmers need a simple tool to evaluate forage productivity under widely varying precipitation conditions. The objectives of this study were to (i) quantify the relationship between crop water use and dry matter (DM) yield for corn (Zea mays L.), foxtail millet (Setaria italica L. Beauv.), and winter triticale (X Triticosecale Wittmack); and (ii) determine the range and distribution of expected DM yields for these three crops in the central Great Plains based on historical precipitation records. The three crops were grown in a dryland no-till corn–millet–triticale sequence from 1998 through 2004 at Akron, CO. Dry matter production was linearly correlated with water use for all three crops, with regression slopes ranging from 24.2 (corn) to 33.0 kg ha–1 mm–1 (millet). Water use efficiency varied widely from year to year (0–32.2 kg ha–1 mm–1) for the three crops, as influenced by growing season precipitation and time of year in which the crops were grown. Millet and triticale produced similar amounts of DM for a given water use, while corn produced less. Precipitation use efficiency for the millet–triticale–corn forage system was 8.7 kg ha–1 mm–1, suggesting this as an efficient forage system for the region.

Abbreviations: DM, dry matter • ET, evapotranspiration • GSP, growing season precipitation • WUE, water use efficiency


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
PROFITABLE agricultural operations in the semiarid central Great Plains must make efficient use of limited and highly variable precipitation. Additionally, cropping systems should be diversified, employing crop rotation systems that minimize disease, weed, and insect problems associated with monoculture. Further, those systems need to ensure that sufficient crop residues remain after harvest to protect the soil surface from wind erosion and to maximize precipitation storage efficiency during the noncrop periods. A recent review of cropping systems across the Great Plains region of North America (Nielsen et al., 2005a) indicated that systems using forages generally had greater WUE and precipitation use efficiencies (based on both mass produced per unit of precipitation received and gross value of product per unit of precipitation received) than systems that did not include forages. Three crops that may have potential to be grown for forage in dryland cropping systems in the central Great Plains region are corn, foxtail millet, and winter triticale.

Corn is often grown for silage under rainfed conditions in the Corn Belt and under irrigation in the semiarid Great Plains, but a defined DM response to water use in dryland production systems has not been reported. Many dryland farmers in the central Great Plains are reluctant to plant corn because of the high input costs and the highly variable nature of corn grain yield associated with variable precipitation during critical reproductive and grain filling growth stages (Nielsen et al., 1996, 2005b). Because corn DM production is not as highly influenced by reproductive stage precipitation as grain production, farmers may discern less risk and be more inclined to include corn for silage in their cropping systems. Haynes (1948) reported that vegetative growth of individual corn plants grown in a greenhouse study was reduced as water supply to the growing plants was restricted, but a water use/DM production function was not defined. Olson (1971) did report dryland corn DM and water use values for eastern South Dakota, but did not note a DM response to water use. The average DM production reported in that study was 8457 kg ha–1 for 313 mm of water use. Hattendorf et al. (1988) found irrigated corn in eastern and western Kansas produced an average of 20 075 kg ha–1 DM for 565 mm of water use, but no production function was reported and the water use values extended only over a very narrow range (561–584 mm). d'Andria et al. (1997) reported corn DM and water use values from southern Italy over a water range of 163 to 632 mm from which we constructed the following water use/DM production function:

Formula
where DM is dry matter (kg ha–1) and ET is evapotranspiration (mm). The large positive offset may be the result of lower calculated ET for each DM point, as they ignored all precipitation events <10 mm over a 24-h period.

We determined another production function for corn DM from combined data reported by Kasele et al. (1994) from dryland and limited irrigated corn in eastern Colorado (239 mm < ET < 294 mm) and by Howell et al. (1995) from variably irrigated corn in the Texas Panhandle (383 mm < ET < 973 mm):

Formula
Nielsen (2004) reported an unpublished DM production function for dryland corn grown in northeastern Colorado under a variety of cropping systems from 1992 to 1997 of

Formula
over an ET range of 250 to 450 mm.

Foxtail millet is one of the earth's oldest cultivated crops, being grown primarily for forage in the USA (Baltensperger, 1996). As a short-season forage crop, it provides the opportunity to immediately follow its harvest in late August with winter triticale planted in late September of the same year. Foxtail millet variety trial data from the Nebraska panhandle (Weichenthal et al., 1998) reported DM production ranging from 2554 to 6283 kg ha–1, but no precipitation records or water use data were reported to help explain the DM differences. Two years of foxtail millet data from South Dakota (Twidwell et al., 1992) showed no consistent response to precipitation, with yields averaging 4050 kg ha–1 over a range of growing season precipitation of 80 to 200 mm. Three years of pearl millet (Pennisetum glaucum L.) forage production at Bushland, TX (Unger, 2001) showed average DM production of 3670 kg ha–1 and average WUE of 13 kg ha–1 mm–1. No water use/DM production functions were found in the literature for foxtail millet.

Triticale results from a cross between wheat and rye (Secale cereal L.). Presently, the majority of triticale grown in the USA is harvested as forage for livestock feed (Stallknecht et al., 1996). There are no reports of water use/DM production functions for winter triticale. One such function can be constructed from data reported by Unger (2001):

Formula
This relationship is useful only in the ET range over which data are reported (237 mm < ET < 412 mm) and may have a questionable slope and intercept due to being based on only three data points. Further evidence of winter triticale's DM response to available water is found in DM yield response functions to precipitation that can be determined from a number of published DM and growing season precipitation (GSP, mm) data sets:

Formula

Formula

Formula

Formula

Formula

Formula

Both agricultural producers and lenders would like to have a means of assessing the risk level that might be incurred in moving from conventional wheat–fallow production systems to more intensively cropped no-till forage systems. Part of that risk assessment involves quantifying the effects of highly variable available water conditions on DM production of potential forage species. Therefore, the objectives of this study were to (i) quantify the relationship between crop water use and DM yield for corn, foxtail millet, and winter triticale under dryland conditions, and (ii) determine the range and distribution of expected DM yields in the central Great Plains based on historical precipitation records.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
This study was conducted at the USDA Central Great Plains Research Station, 6.4 km east of Akron, CO (40°09' N, 103°09' W, 1384 m). The soil type was a Weld silt loam (fine, smectitic, mesic Aridic Argiustoll). In 1990, several rotations were established to investigate the possibility of cropping more frequently than every other year, as done with the traditional winter wheat–fallow system. A description of the plot area, tillage systems, and experimental design are given in Bowman and Halvorson (1997) and Anderson et al. (1999). Briefly, rotation treatments were established in a randomized complete block design with three replications. All phases of each rotation were present every year. Individual plot size was 9.1 by 30.5 m, with east–west row direction.

The current study analyzes data beginning with the 1998 crop year when a rotation was introduced that used only crops for forage production (corn followed by foxtail millet followed by winter triticale) with no fallow period. Crops grown before the initiation of this forage system evaluation were corn before the millet phase, winter triticale before the corn phase, and 11-mo fallow before the triticale phase. The corn hybrids were all 99-d relative maturity hybrids planted at recommended dryland rates. The rotation used contact and residual herbicides for all weed control. Specific details regarding hybrids and varieties, planting and harvest dates, and seeding and fertilization rates are given in Table 1. Twelve corn plants were harvested from a single row of each plot (approximate harvest sample area of 3.7 m2) at late dough (R4) or early dent (R5) for DM determination. Both millet and winter triticale were harvested when fully headed but before anthesis from a harvest sample area of either 4.1 or 2.9 m2. Samples were oven-dried at 60°C to constant weight.


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  		Table 1. Planting, harvesting, and fertilizing details for corn–millet–winter triticale forage system, Akron, CO, 1998 to 2004.

 
Crop water use was calculated by the water balance method using soil water measurements at planting and harvest, and assuming runoff and deep percolation were negligible. The soil water measurements in the 0.0- to 0.3-m layer were made by time-domain reflectometry. Soil water measurements at 0.45-, 0.75-, 1.05-, 1.35-, and 1.65-m depths were made with a neutron probe. The neutron probe was calibrated against gravimetric soil water samples taken in the plot area. Gravimetric soil water was converted to volumetric water by multiplying by the soil bulk density for each depth. Two measurement sites were located near the center of each plot and data from the two sites were averaged to give one reading of soil water content at each sampling depth per plot.

Available water per sampling depth was calculated as:

Formula
where volumetric water = m3 water m–3 soil from neutron probe or time-domain reflectometry, lower limit=lowest volumetric water observed under these crops in the plot area (Ritchie, 1981; Ratliff et al., 1983), and layer thickness = 300 mm.

The specific values of lower limits used are given in Table 2. Daily precipitation was recorded as the average of measurements made at two diagonally opposite corners of the 7.8-ha plot area.


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  		Table 2. Lower limits of volumetric soil water used to calculate available soil water for foxtail millet, winter triticale, and corn on a Weld silt loam, Akron, CO.

 
Dry matter, water use, and WUE were evaluated for crop species differences by analysis of variance, with years considered as a random variable (Gomez and Gomez, 1984). The relationships between crop water use and DM yield were analyzed by linear regression. Statistical analysis was performed using Statistix 8 software (Analytical Software, 2003). Both linear and quadratic regression models were tested. Linear regression slopes and intercepts were compared for significant differences using the Statistix 8 Comparison of Regression Lines procedure.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Precipitation was highly variable from year to year, and from growing season to growing season within a year for the three crops (Table 3), resulting in a significant year by crop interaction effect for water use (p < 0.01), DM (p < 0.01), and WUE (p < 0.01). Consequently, the data are presented and discussed by year.


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  		Table 3. Precipitation at Akron, CO (1998–2004 and 93-yr average).

 
Corn water use ranged from 146 (2002) to 316 mm (2001), averaging 256 mm (SE = 25 mm) (Fig. 1 ). Millet water use ranged from 70 (2002) to 266 mm (2003), averaging 186 mm (SE = 28 mm). Winter triticale water use ranged from 86 (2000) to 330 mm (2003), averaging 205 mm (SE = 36 mm). Differences in water use between crops were significant in 6 of 7 yr (p < 0.05), with corn having the greatest water use in 5 of those 6 yr.


Figure 1
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  		Fig. 1. Crop water use for corn, foxtail millet, and winter triticale grown for forage at Akron, CO, 1998 to 2004. (p = probability that the null hypothesis of no difference in water use due to crop species is true.)

 
Corn DM ranged from 0 (2002) to 6132 kg ha–1 (2001), averaging 2930 kg ha–1 (SE = 767 kg ha–1) (Fig. 2 ). Millet DM ranged from 0 (2002) to 5638 kg ha–1 (2003), averaging 3155 kg ha–1 (SE = 844 kg ha–1). This was 28% lower than the 3-yr average foxtail millet DM of 4382 kg ha–1 reported by Weichenthal et al. (1998) for the Nebraska panhandle, but only 9% lower than the 3-yr average of 3479 kg ha–1 reported by Peterson et al. (2001) for an opportunity cropping system in northeastern Colorado. Persistent dry conditions in 2002 resulted in withering and failure to produce any harvestable corn or millet forage. Winter triticale DM ranged from 731 (2000) to 10 632 kg ha–1 (2003), averaging 3916 kg ha–1 (SE = 1322 kg ha–1). This value is nearly the same as the 3-yr average triticale DM yield of 3913 kg ha–1 reported by Peterson et al. (2001) measured in a triticale–corn–forage soybean rotation in northeast Colorado. Dry weight of all three crops in the current study was greatly affected by growing season precipitation. For example, the maximum winter triticale DM was observed in 2003 when growing season precipitation was 143% of normal. At the other extreme, no corn DM was harvested in 2002 when growing season precipitation was only 56% of normal. The average DM was not significantly different (p < 0.05) in 4 of 7 yr among the three crops.


Figure 2
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  		Fig. 2. Harvest dry matter for corn, foxtail millet, and winter triticale grown for forage at Akron, CO, 1998 to 2004. (p = probability that the null hypothesis of no difference in dry weight due to crop species is true.)

 
Corn WUE ranged from 0.0 to 19.4 kg ha–1 mm–1, averaging 10.5 kg ha–1 mm–1 (SE = 2.5 kg ha–1 mm–1) (Fig. 3 ). This is approximately the same as the 9.3 kg ha–1 mm–1 of rainfed corn in northern Texas reported by Howell et al. (1995). Millet WUE ranged from 0.0 to 22.0 kg ha–1 mm–1, averaging 14.3 kg ha–1 mm–1 (SE = 3.5 kg ha–1 mm–1). Winter triticale WUE ranged from 8.5 to 32.2 kg ha–1 mm–1, averaging 16.5 kg ha–1 mm–1 (SE = 2.9 kg ha–1 mm–1). This value is not greatly different from the 4-yr average WUE of 14 kg ha–1 mm–1 (for triticale forage) and 18 kg ha–1 mm–1 (for total triticale plant material) reported by Unger (2001) in northern Texas. In the current study, WUE was significantly different among crops only in 2002 and 2003, and in both of those years triticale had the highest WUE. The average WUE was not significantly different (p < 0.05) in 5 of 7 yr among the three crops.


Figure 3
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  		Fig. 3. Dry matter water use efficiency for corn, foxtail millet, and winter triticale grown for forage at Akron, CO, 1998 to 2004. (p = probability that the null hypothesis of no difference in water use efficiency due to crop species is true.)

 
Water use efficiency was greatly affected by precipitation amount and distribution in each year. Because each crop is grown in a different time period of each year, direct comparisons of WUE between crops in a given year may not be informative about relative crop WUE. The relationship between DM and WUE (Fig. 4 ) allows for a more direct comparison of WUE between crops. Slopes of WUE vs. DM for millet and corn are not different from each other (p = 0.23), but are both different from winter triticale (p < 0.05). Winter triticale exhibited greater WUE under conditions that produced low DM (<3000 kg ha–1). Extending the regression line for corn slightly beyond its greatest DM data point indicates that corn and winter triticale used water with similar efficiency at yields of about 7000 kg ha–1. Millet and winter triticale used water with similar efficiency at yields of about 3500 kg ha–1. These differences in WUE are most likely due to the generally cooler conditions that winter triticale grew under compared with millet and corn which grew during the warmer summer months.


Figure 4
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  		Fig. 4. Water use efficiency vs. dry matter yield for foxtail millet, winter triticale, and corn at Akron, CO, 1998 to 2004.

 
Dry weights of all three crops increased linearly with increasing water use (Fig. 5 ). Only the winter triticale data set showed improved fit with a quadratic model, primarily because of the very high yield (10 632 kg ha–1) observed in 2003 (Fig. 2) with a water use of 330 mm. Because of the commonly observed linear relationship between water use and DM, and the single triticale data point indicating a quadratic response, we chose to analyze only differences in linear responses between the three crops. Additional data will need to be collected at water use values >350 mm to confirm a quadratic DM response to water use for winter triticale.


Figure 5
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  		Fig. 5. Harvest dry matter vs. water use with fitted linear regression responses for corn, foxtail millet, and winter triticale grown for forage at Akron, CO, 1998 to 2004.

 
The slopes of the three linear regression lines shown in Fig. 5 were not different from one another (p = 0.67). The water use (x axis) offset shown in Fig. 5 was significantly greater for corn (p < 0.01) than for millet or winter triticale (135 mm vs. 78 or 86 mm), probably the result of wider row spacing in corn leading to more soil surface exposed and increased evaporation following precipitation. The linear regression fit the observed data better for millet (r2 = 0.84) and winter triticale (r2 = 0.82) than for corn (r2 = 0.61).

The regression slope of 24.2 kg ha–1 mm–1 for corn in the current study is similar to those we generated and discussed earlier in this paper for data from southern Italy (23.0 kg ha–1 mm–1) (d'Andria et al., 1997) and from Texas and Colorado (26.2 kg ha–1 mm–1) (Howell et al., 1995; Kasele et al., 1994). As discussed earlier, the large positive offset for the generated Italian production function may be due to the researchers' nonreporting of precipitation events <10 mm over a 24-h period. The production function generated from the Texas and Colorado data produced greater DM yields at similar water use values than the production function generated in this study. This may be the result of the greater plant populations and fertilizer applications and longer-season hybrid used in the irrigated Texas study. The current corn production function was nearly identical to the one reported by Nielsen (2004) for corn in northeastern Colorado from 1992 to 1997 [DM = 22.4 x (ET – 129)]. This is not surprising considering that the data for that relationship came from a study with similar soil type, plant population, corn hybrid, and fertility (although years of observation were different).

The regression slope for winter triticale (33.0 kg ha–1 mm–1) was similar to the slope for several of the regressions of DM on GSP we generated earlier in the paper from previously published data sets from Cyprus (32.0 kg ha–1 mm–1), Saskatchewan (34.4 kg ha–1 mm–1), and Alberta (36.1 kg ha–1 mm–1), but much greater slope than the generated production function slope from Texas of 12.7 kg ha–1 mm–1. As mentioned earlier, that constructed regression was based on only three data points over a small ET range of 237 to 421 mm, so the slope may not be an accurate reflection of the true winter triticale DM response to water use. The production function for winter triticale given in Fig. 5 estimates a DM yield of 10 360 kg ha–1 for 400 mm ET, much greater than the 6575 kg ha–1 estimated by the Texas production function at that level of ET. The reasons for the lower winter triticale yields in the Texas study compared with the current study are not readily apparent.

Using these regression relationships to estimate the distribution of expected DM production from the historical precipitation record requires some estimate of soil water use by the three crops. Planting and harvest observed soil water readings averaged over 1998 to 2004 are shown in Fig. 6 . Corn and millet show strong water extraction in the 0.0- to 0.9-m soil layer and slight water extraction in the 0.9- to 1.2-m layer. Ending soil water contents under winter triticale were nearly the same as beginning soil water contents, so it is difficult to infer rooting depth. Winter triticale appears to be making all of its growth from precipitation that falls during the growing season (including the overwinter period), and not from soil water stored before planting. There was no measurable recharge between millet harvest in late August and winter triticale planting in late September. Because of the cropping intensity of winter triticale following millet, there was no appreciable soil water recharge at soil depths below 0.9 m.


Figure 6
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  		Fig. 6. Volumetric water content at planting and harvest for corn, foxtail millet, and winter triticale grown for forage at Akron, CO, 1998 to 2004. Values on right side of figure are probability (p) that the null hypothesis of no difference between planting and harvest volumetric water contents is true.

 
From the average soil water content data shown in Fig. 6, we determined average seasonal soil water use of 70 mm for corn, 66 mm for millet, and 8 mm for winter triticale. These soil water use amounts were added to the growing season precipitation record from 1965 to 2004 at Akron, CO to provide a range and distribution of water use values to use with the production functions shown in Fig. 5. The period of precipitation was 14 May to 26 August for corn, 25 June to 26 August for millet, and 24 September to June 17 for winter triticale. The calculated water use values for millet and winter triticale all fall within the range of values used to establish the production functions, except for the upper 5% of the millet values and the upper 8% of the winter triticale values. There were quite a few years in the historical precipitation record that were wetter during the corn growing season than during the data collection years of this study, such that 23% of the calculated water use values were beyond the range of the data used to establish the production function for corn. Therefore, the estimated DM histograms (Fig. 7 ) result from some extrapolation of the production functions beyond the water- use values used to generate them.


Figure 7
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  		Fig. 7. Frequency distributions of estimated dry matter production for corn, foxtail millet, and winter triticale at Akron, CO based on growing season precipitation (1965–2004) and water use/dry matter production functions.

 
Estimated corn DM production ranged from 1052 to 9270 kg ha–1 (mean 3820 kg ha–1). Dry matter production of 2000 to 4000 kg ha–1 would occur 43% of the time (Fig. 7). Estimated millet DM production ranged from 422 to 6465 kg ha–1 (mean 3283 kg ha–1). Dry matter production was also most frequently estimated to occur in the 2000 to 4000 kg ha–1 range (53% of the time). Winter triticale DM production was estimated to occur over a broader range (527–12 623 kg ha–1), and averaged greater than corn and millet (mean 5367 kg ha–1). Winter triticale DM production was most frequently estimated to occur in the 4000 to 6000 kg ha–1 range (39% of the time). Dry matter production of at least 4000 kg ha–1 would be expected to occur in 45, 30, and 75% of years for corn, millet, and winter triticale, respectively. Based on this analysis, there may be less downside risk in producing a profitable forage crop with winter triticale than with corn or millet.

Precipitation use efficiency for this all-forage cropping system can be calculated by taking the total production of DM by the three crop species (23 334 kg ha–1) over the 7 yr of the study and dividing by the total precipitation that fell over that period (2696 mm). Doing so gives a precipitation use efficiency of 8.7 kg ha–1 mm–1. This value is lower than precipitation use efficiency values calculated by Nielsen et al. (2005a) for data from Unger (2001) for continuous forage triticale and continuous forage wheat (about 14 kg ha–1 mm–1) in northern Texas. This is most likely due to the corn and millet crop failures during the 2002 drought and the frequently lower WUE of corn comprising 33% of our cropping system area each year. Our precipitation use efficiency of 8.7 kg ha–1 mm–1 was greater than precipitation use efficiency for grain-based systems at this location, which ranged from 2.8 to 5.9 kg ha–1 mm–1 (Nielsen et al., 2005a) because of the lower photosynthetic energy requirements of forage production vs. grain production (Penning de Vries, 1975).


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Corn, foxtail millet, and winter triticale DM increased linearly with water use, responding similarly to increases in water use. Because of a larger water use offset for the corn water- use/DM production function compared with millet and winter triticale production functions, corn produced less DM for a given water use than millet and winter triticale. Using the production functions determined in this study with historical precipitation records gave estimated average corn, millet, and winter triticale DM yields of 3820, 3283, and 5367 kg ha–1, respectively. Winter triticale has a greater probability of achieving a DM yield of at least 4000 kg ha–1 than either corn or millet. Precipitation use efficiency of this corn–millet–winter triticale dryland forage system was greater than that reported for grain-based dryland systems. Additional work should be done to determine the productivity and benefits of including a broadleaf species such as forage pea, kenaf, or forage soybean into dryland forage production systems that use grasses.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 





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