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Published online 20 September 2006
Published in Soil Sci Soc Am J 70:1951-1956 (2006)
DOI: 10.2136/sssaj2005.0288
© 2006 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Nutrient Management & Soil & Plant Analysis

Winter Cereal–Corn Double Crop Forage Production and Phosphorus Removal

Bradford D. Brown*

Univ. of Idaho, Parma Research and Extension Center, 29603 U of I Lane, Parma, ID 83660

* Corresponding author (bradb{at}uidaho.edu)


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Maximizing P removal with cropping can increase regulated P-based manuring rates or reduce soil test P in manure-enriched soils. The potential for increased P removal with winter forage–corn silage double cropping was evaluated in a 3-yr study at Parma, ID. Winter barley (Hordeum vulgare L.), and both winter and spring genotypes of wheat (Triticum aestivum L.) and triticale (xTriticosecale Wittmack) were fall planted at three seeding rates (112, 168, or 224 kg ha–1) and followed with silage corn (Zea mays L.). Corn alone and a noncropped treatment were included. Winter forages were harvested near boot stage. Seeding rates of 168 kg ha–1 were necessary for maximizing winter forage production but had little effect on P uptake. Winter forage production and P content were highly year dependent due largely to appreciable winterkill of spring wheat and winter barley in 1999. Winter forage P concentrations, unlike those for corn, decreased with successive harvests. Cumulative P uptake ranged as high as 65.7 kg ha–1 for winter triticale. Winter forages reduced corn yields in 2 of 3 yr and corn P uptake in 1 yr. Compared to corn alone, double cropping increased cumulative forage production from 8.4 to 15.9% and total P removal by 29.8 to 42.2%. Soil test P concentrations after 3 yr decreased more with double cropping than with corn alone. Half of the P decline was unrelated to P uptake and removal. Double cropping can increase total forage production, P removal, and hasten soil test P decline.

Abbreviations: CAFO, confined animal feeding operations • Olsen P, 0.5 M NaHCO3 extractable P • PRI, P removal index


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
SURFACE WATER quality concerns have led to P-based limitations on manuring rates from confined animal feeding operations (CAFO). For P-based manuring, the primary limitation to higher manuring rates, other than manure P concentration, is the amount removed by the cropping system. Land resources with many CAFO are limited and more manure P is generated than can be removed with single annual crops. Increasing on-farm forage production and reducing purchased forages could improve the P balance for whole farms (Wang et al., 2000; Rotz et al., 2002). Increasing crop P uptake is important for improving the P balance in western dairies (Spears et al., 2003). Greater P removal with cropping would (i) slow or avoid soil P enrichment, (ii) enable herd size to be maintained or expanded to an economic scale, (iii) preclude the need for increased land resources or capital improvements to extend manure distribution systems, or (iv) hasten soil test P decline in previously P-enriched soil and reduce environmental risks of runoff P.

Phosphorus removal with double and triple crop forage systems for the southern USA was reviewed (Newton et al., 2003; Pant et al., 2004), but information is limited for areas with shorter growing seasons. Double crop (winter cereal–corn) forage systems for the intermountain western USA have potential for increasing crop P removal over that removed with corn alone, as well as increasing forages otherwise used in the CAFO enterprise. Ideally, fall planted winter cereals produce additional forage during the cooler part of the year without limiting the corn growing season and sacrificing corn production. Winter cereals harvested at or near the boot stage, rather than soft dough, are less productive, but the earlier harvest allows corn to be planted at near normal planting dates. Furthermore, winter cereal P accumulation precedes biomass production. For irrigated wheat, no postanthesis P uptake was reported (Manske et al., 2001) and others indicated that maximum P uptake occurred by heading (Miller, 1939; Boatwright and Haas, 1961). Thus, a boot stage harvest does not sacrifice P uptake and removal nearly as much as it does biomass.

Crop production practices may differ for maximizing boot stage winter cereal forage production and P removal from winter cereals grazed or produced for grain. The restrictions associated with double cropping can limit crop management options such as winter cereal planting dates. Whereas winter cereals produced in the U.S. Great Plains for grazing are planted earlier than normal to maximize fall forage (Lyon et al., 2001), late summer planted winter cereals may not be an option in a double cropping system where full season corn hybrids require late summer harvest dates to maximize their silage yield potential. Higher winter cereal seeding rates are used for fall grazing or early spring forage production than for grain (Hanaway et al., 1983; Watson et al., 1993; Holman et al., 2005). Information is needed on appropriate seeding rates for boot stage dry matter production and boot stage P uptake.

Winter cereals may differ in their potential for boot stage forage and P removal. Rye (Secale cereale L.) typically grows under cooler temperatures than winter wheat or winter barley, and can produce more vegetative biomass from late fall through early spring (Hanaway et al., 1983; Watson et al., 1993; Moyer and Coffey, 2000). The most common winter cereal currently used for boot stage forage in the intermountain western USA is triticale, the wheat x rye cross. There are few reports of winter cereals compared for both boot stage forage dry matter and P removal potential.

Spring cereal genotypes are fall planted in some areas where winters are mild enough that plants are not lost to low winter temperatures. We have observed fall planted spring genotypes that headed earlier than winter genotypes. Winter triticale genotypes required more growing degree days than spring genotypes to reach maximum main stem elongation and dry matter accumulation (Royo and Blanco, 1999). Earlier plant development and harvest could result in higher early spring biomass production, if not more time for subsequent seedbed preparation or a longer growing season for corn silage.

The general objective of this study was to evaluate the winter cereal–silage corn double crop system for its potential to increase both forage production and P removal over that with corn alone as a single crop. The specific objectives were to compare fall planted winter and spring cereals for their boot stage forage and P removal potential, and evaluate seeding rates for their importance in both forage yield and P removal.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
A 3-yr, irrigated double-crop (small grain boot stage harvest followed by silage corn) forage study was conducted at the University of Idaho Parma Research and Extension Center in a Greenleaf-Owyhee silt loam (fine-silty, mixed, superactive, mesic Xeric Calciargid). The double cropping involved three winter (barley, wheat, and triticale) and two spring (wheat and triticale) cereals all fall planted at three seeding rates (112, 168, or 224 kg ha–1) and followed in the spring with silage corn. Two nonplanted fall treatments were also included, one used for a single crop of silage corn and the other fallowed in both winter and summer for the duration of the study. Treatments were repeated every year in the same plot so that cumulative treatment effects on soil test P after 3 yr could be determined. Treatments were arranged in a randomized complete block design with four replications. Individual plots were 1.5 by 9.1 m. The previous crop was alfalfa (Medicago sativa L.).

Soil samples were collected (0–30 cm depth) before establishment of the trial to characterize the site's fertility. Initial 0.5 M NaHCO3–extractable P (Olsen et al., 1954), hereafter referred to as Olsen P, measured 19.8 mg kg–1. Other soil measures included saturated paste pH of 7.3, 1.0 dS m–1 electrical conductivity, 11.5 g kg–1organic matter, and 30 g kg–1 calcium carbonate equivalent. Other nutrients were adequate based on University of Idaho fertilizer recommendations for irrigated winter wheat (Brown, 1986) or were applied. The study area received a uniform application of 180 kg P ha–1 (as 0–19.3–0) on 21 Oct. 1998 to raise the initial Olsen P soil test to above 30 mg P kg–1. The soil was then disked to a depth of 15 cm and harrowed for a seedbed. Subsequent tillage (disking, rototilling) was confined as much as possible within each plot using implements that fit the plot width.

Fall planted forages included ‘Trical 815’ winter triticale, ‘Trical 2700’ spring triticale, ‘Stephens’ soft white winter wheat, ‘Penawawa’ soft white spring wheat, and ‘Hoody’ winter barley. Seed beds for winter forages involved disking corn stubble and culti-packing. Planting dates for winter forages were 21 Oct. 1998, 27 Sept. 1999, and 3 Oct. 2000. Winter cereals were drill planted in seven rows spaced 16.4 cm apart. Residual nitrate N (0–30 cm) before planting winter forages measured 34 and 48 mg kg–1 in fall 1998 and fall 1999, but was not measured in fall 2000. Nitrogen fertilizer as urea was top-dressed 16 Apr. 1999, 24 Apr. 2000, and 23 Mar. 2001 at rates of 112 kg N ha–1 in 1999 and 2000 and 224 kg N ha–1 in 2001. Winter forage winter survival was measured 19 Mar. 1999 from plant counts in 0.45 m2. All winter forages were furrow irrigated as needed. Winter forage biomass was measured 20 May 1999, 27 Apr. 2000, and 11 May 2001. The cereals were at the early to late boot stage, Feekes 10.1–10.2 (Large, 1954). Total biomass fresh weight in plot centers was harvested from 4.64 m2 using a 60-cm-wide flail chop forage harvester (Swift Machine and Welding, Ltd., Swift Current, SK) and weighed. Subsamples (3.7 L) of the harvested biomass were weighed, dried at 60°C, and reweighed for the moisture content determination. All remaining forage was removed from the plot area.

Winter forage and subsequent corn plot width was dictated by planting equipment and available field space, and there was limited (winter forages) or no (corn) border between harvested plots. Minimal 30- to 35-cm borders on each side of the winter forage harvest strip were less than desirable borders from plot edges, but edge effects extending into harvest strips were not visible. Wheat genotypes were about 25 cm shorter at harvest than other winter forages (data not shown) and their relative performance may be biased. The edge effects, especially from noncropped adjoining plots, likely contributed to the winter forage yield, P uptake, and P concentration data variability, but this did not preclude showing significant year, forage, and year x forage treatment effects.

A corn hybrid (‘Pioneer 3395IR’ in 1999 and ‘Cropland 676RR’ in 2000 and 2001) was planted within 1 to 7 d after cereal forage harvest using a conventional planter with double disk openers. The row spacing was 75 cm and target plant populations were 86 000 plants ha–1 in 1999 and 2000 and 94 000 ha–1 in 2001. Corn was planted into the winter cereal stubble without tillage on 20 May the first year and poor stands resulted from some treatments. Therefore, the corn plant population after the winter forage treatments was measured each year from 11.6 m2. Corn vigor ratings (scale 1 = poor, 4 = good) were visually estimated only in 1999 when there were obvious differences. Given the difficulty establishing no-till corn in 1999, winter forage stubble in 2000 and 2001 was rototilled to 7.6 cm and the soil culti-packed before planting 3 May 2000 and 14 May 2001. Roundup Ready corn was planted in the last 2 yr to assist in the control of the winter cereal regrowth. Terbufos insecticide, S-[[(1,1-dimethylethyl)thio]methyl] O,O-diethylphosphorodithioate was applied in the seed row at the rate of 350 g ha–1 in 2000 only. Glyphosate, N-(phosphonomethyl)glycine in the form of its isopropylamine salt, at 1.12 kg ha–1 was applied postemergence in 2000 and 2001 for weed control. Fertilizer N for corn was applied as urea side-dressed 29 June 1999 (224 kg N ha–1), 30 May (134 kg N ha–1), and 21 June 2000 (168 kg N ha–1). Urea was preplant broadcast and incorporated 14 May 2001 (224 kg N ha–1). Corn was irrigated in furrows located equidistant between the rows.

Corn harvest dates were 21 September, 19 September, and 5 September in 1999, 2000, and 2001, respectively. Total biomass was harvested by hand from 11.6 m2 (the two 75-cm beds comprising the plot) and weighed. There were no borders for corn plots as the entire width of the plot was harvested. Edge effects from most neighboring treatments were considered minimal in that corn growth after the first year did not differ among winter forage treatments. As with winter forages, edge effects were likely appreciable when corn with no border was located next to noncropped plots and the associated variability may have contributed to the lack of treatment significance in some years.

Four corn plants were flail chopped and subsamples (3.7 L) weighed, dried, and reweighed for the moisture determination. The subsamples of fall and summer forages were ground to pass a 1-mm screen before chemical analysis. The total P concentrations were determined by ICP using a macro-element screen (Anderson, 1996).

Soil samples (0–30 cm, composite of 8 cores plot–1) from all treatments, including all seeding rates, were collected after the first (fall 1999) and last (fall 2001) corn harvest. Samples were air dried, ground to pass a 2-mm screen, and Olsen P was determined colorimetrically (Murphy and Riley, 1962). A P Removal Index (PRI) was calculated for a cropping system's efficiency in lowering soil test P (0–30cm). The final Olsen P for each plot of a cropped treatment was subtracted from the overall mean for the noncropped treatment (21.8 mg kg–1) and the difference divided by the cumulative P removed from the same plot. The PRI indicates the P required to change Olsen P 1 mg kg–1 beyond what it would be without cropping while adjusting for the natural decline in Olsen P.

With the exception of winter forage winterkill and corn vigor, winter forage, corn, and double crop data were combined and analyzed across years. Olsen P data were analyzed across the first and last corn silage harvest years. The analyses of variance were performed using SAS version 8.01 (SAS Institute, 2001). A protected LSD was calculated for main effects significant at the 0.05 probability level.


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
Winter Forages
Small grain winter forages differed in dry matter yield in some years (Tables 1 and 3). Winterkill reduced winter barley stands 23% and spring wheat stands 45% in 1999 (Tables 2 and 4) resulting in considerably less forage production than with spring and winter triticale or winter wheat. There was no winterkill observed in 2000 and 2001, and forage production did not differ as widely as in 1999. Forage yield for winter barley rebounded in the second year, in the absence of winterkill, yielding more than all other forages. Spring wheat forage yield also rebounded the second year and did not differ significantly from the two triticales and exceeded the yield for winter wheat. Rebounding spring wheat and winter barley yields in 2000 are possibly related to the poorer yields or stands in 1999. Spring genotypes in the absence of winterkill were as productive as winter genotypes of the same specie. Winter wheat was consistently lower yielding than either winter or spring triticale (P < 0.10).


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  		Table 1. Multiple year analysis of variance for winter forage, corn, and their combination (double crop).

 

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  		Table 3. Mean winter grown forage dry matter yield, P concentration, and P uptake by year and by winter or spring cereal.

 

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  		Table 2. Single year analysis of variance for winter forage winterkill and spring corn vigor in 1999 and the P removal index in 2001.

 

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  		Table 4. Previous winter grown forage winterkill and subsequent corn plant population per plot and vigor in 1999.

 
Triticale forage production, unaffected by winterkill, declined during the 3-yr study. All winter forage yields declined from 2000 to 2001 when production across all winter forages averaged only 80% as much as in 2000. Cumulative growing degree days (base 0°C) from planting to harvest were 14.2% fewer in 2001 than in 2000 (1255 vs. 1463), and the lowest of all years.

Three-year mean winter forage yields were 5.39, 5.86, and 5.97 Mg ha–1 for the 112, 168, and 224 kg ha–1 seeding rates, respectively. Seeding rates higher than 112 kg ha–1 were required to maximize forage yield (P < 0.01). Forage yields from the lowest seeding rate ranged from 88 to 94% of those with 168 kg seed ha–1. Forage yields for the two highest seeding rates did not differ. There were no significant interactions for yield involving seeding rates.

Mean winter forage P concentrations declined from the first year high of 3.91 g kg–1 in 1999, to 3.15 g kg–1 in 2000, and to 2.48 g kg–1 in 2001 (Tables 1 and 3). Declining forage P concentrations were attributed to reduced available soil P with crop removal. Higher winter barley and spring wheat P concentrations in 1999 relative to 2000 may also be due to reduced plant populations and less competition for available P.

Forage P concentrations among forages differed in some years, but they were not consistent (Table 3). For example, spring triticale P concentrations were lower than those of winter barley in 1999, but higher than winter barley in 2000. Spring wheat was lower in P concentration than winter barley in 1999, lower than the triticales and winter wheat in 2000, but did not differ from other winter forages in 2001. Winter wheat tended to have higher P concentrations than spring wheat but differed significantly only in 2000. Lower P concentrations in spring genotypes relative to winter genotypes of the same species is consistent with more advanced plant development of spring genotypes at sampling. Seeding rates did not significantly affect winter forage P concentrations.

Phosphorus uptake differed among forages depending on the year, but mean winter forage P uptake over the 3 yr was greatest for winter triticale (Table 3). Winter forage P uptake by winter barley and especially the fall planted spring wheat was reduced in 1999 due to winterkill. With no winterkill, winter forages differed less in P uptake, and P uptake in 2001 did not differ among forages. Uptake of P in winter barley with no winterkill was comparable to triticale and as high or higher than winter wheat. Winter forage seeding rates did not affect P uptake.

Triticale and winter wheat P uptake declined with each subsequent winter forage harvest, the decline ranging from 46% for winter wheat to 54% for winter triticale (Table 2). Mean P uptake across all winter forages declined 38% from 2000 (20.7 kg P ha–1) to 2001 (12.8 kg P ha–1). Declining P uptake resulted from both less biomass and declining forage P concentrations.

It is not clear why dry matter production declined in the final year of the study, other than the fewer GDD in 2001 and the declining available P. Forage P concentrations in the last year are above those previously cited (1.5–2.0 g kg–1) as necessary for the production of grain (Dow, 1980), but those critical ranges may not be appropriate for dry matter production at preanthesis growth stages. Whole plant P critical ranges for field grown boot stage forage production are not widely reported. Whole plant winter wheat dry matter yields were linearly related to whole plant P concentrations above 4 mg kg–1 in some reports (Sharpley, 1985; Bolland, 1991) but the growth stages were not given. The dependence of the critical P concentration for grain yield in whole tops is highly dependent on the growth stage when collected (Bolland and Paynter, 1994). Additional study of the critical P concentration necessary for maximizing winter cereal boot stage forage production is needed.

Silage Corn
Previous winter forages affected corn silage yields more in some years than others (P < 0.001, Tables 1 and 5). Corn silage dry matter yields decreased in 1999 when corn was no-till planted into stubble of winter forages unaffected by winterkill (winter triticale, winter wheat, and spring triticale) where corn stands were reduced 25 to 32% (Table 4). Corn vigor also decreased in 1999 following winter forages (Table 4), in part due to regrowth of harvested forages. Consequently, corn silage dry matter yields were greater in 1999 following fall planted forages partially lost from winterkill. Corn yields were not affected by previous winter forages in 2000 but in 2001 corn yield was lower following all winter forages. Winter forage seeding rate did not affect corn yield in any year.


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  		Table 5. Mean silage corn dry matter yield, P concentration, and P uptake as affected by years and winter grown forages.

 
In contrast to winter forages, corn forage P concentrations and P uptake did not decline with successive harvests (Table 5). In fact, corn forage P concentrations and P uptake were greatest in 2001, the final year of the study. Winter forages did not affect corn forage P concentrations but higher silage yields caused greater P uptake (P < 0.08) for corn no-till planted in 1999 into winter forages with the least stubble.

Double crop (winter forage and silage corn) dry matter yield did not consistently differ in all years from corn alone (Tables 1 and 6), but over 3 yr was higher by 8.4 to 15.9% (Table 5). Double crop yield over 3 yr for spring wheat and corn was higher than for winter wheat and corn, but did not differ from other double crop combinations. Double cropped forages were appreciably more effective in P removal than corn alone, increasing P uptake by 29.8 to 42.2%. Double crop P uptake did not consistently differ among winter forage–corn combinations, but over 3 yr was higher for the winter triticale–corn combination than for spring wheat and corn, winter wheat and corn, and winter barley and corn.


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  		Table 6. Mean double crop dry matter yield, P uptake, Olsen P after the first and last full crop cycle, and the P removal index as affected by double crop treatments.

 
Unlike corn alone, double cropping over 3 yr essentially removed as much P as was initially applied. To put these results in perspective for P removal based manuring, a difference in three year P uptake of 40 kg ha–1 with double cropping, the minimum difference in this study, would enable >26 Mg ha–1 higher dry manuring rates over the period, assuming a manure P content on a dry matter basis of 1.5 g P kg–1. Manuring rates (or animal units the land resource would accommodate) in a P removal limited system could be increased from 30 to 42% with double cropping over that with corn alone depending on the winter forage used.

These double crop P removal estimates may be conservative for highly enriched soils with much higher initial Olsen P. For highly enriched soils, winter forage P concentrations would probably not decline as rapidly as they did in this study. Winter forage P concentrations would also likely be greater than those reported for the last year of this study, and possibly higher throughout the study. The mean National Research Council P concentration listed for heading stage triticale silage is 3.3 g kg–1 (NRC, 2001).

Longer season silage corn hybrids might possibly be used as a single crop of corn silage, as they could be planted earlier and harvested later by a few days. However, longer season hybrids, even if as productive as double cropping in total forage, would likely still lag in total P uptake due to lower forage P concentrations. Increasing corn silage yield using longer season hybrids in a double crop system would likely come at the expense of the winter forage contribution to total P uptake.

Double cropping would not involve additional equipment for most enterprises already producing swathed and chopped forages. Irrigation requirements would increase somewhat; for winter forage establishment possibly, but primarily to support spring vegetative growth. Winter forages in most dairies in the region are irrigated with storage lagoon water so they provide additional opportunity for emptying lagoons. For P removal based and limited manuring, annual N requirements would increase for this double crop system. Economic comparisons of double cropping with corn alone are confounded in that additional production costs with double cropping must needs be compared also to the economics of manuring alternatives in limited land resource enterprises; additional land purchase, fewer animals, greater transport of manure.

Soil Test Phosphorus
Olsen P declined during the study in both cropped and noncropped treatments (Tables 1 and 6), and differed for noncropped, single, and double cropped treatments (P < 0.0001). Olsen P after the last corn harvest was lower for all double cropped treatments than the Olsen P for corn alone, which was lower than the Olsen P for the noncropped treatment. Olsen P was unaffected by winter forage seeding rates and did not differ significantly among winter forage–corn combinations, ranging narrowly from 11.7 to 12.2 mg kg–1.

The decline due specifically to cropping is the difference in Olsen P for the cropped and noncropped treatments. The Olsen P difference between double cropped and noncropped treatments in fall 2001 after the final harvest was about 10 mg P kg–1. Considering that Olsen P in the noncropped treatment also declined about 10 mg kg–1 over the same period, it appears from this study that crop P removal and natural sorption processes were equally responsible for the Olsen P decline in the double crop treatment. Olsen P decline from appreciably higher initial soil test concentrations than in this trial may exceed those reported here (Eghball et al., 2003). Conversely, we used an inorganic fertilizer P source in this study to raise initial available P, and the decline in soil test P may be greater with fertilizer P than with manure P sources (Laboski and Lamb, 2003).

The PRI for cropping system treatments differed significantly (P < 0.0001). The PRI ranged narrowly from 18.1 to 19.5 for double crop combinations (averaged across seeding rates), all of which differed significantly (P < 0.05) from the PRI for single crop corn (30.4). The reason for this difference is not clear. The PRI could differ for corn if more of the total P removed was from deeper than 30 cm relative to winter forages. Soil temperatures below 30 cm would certainly be cooler with root activity and P uptake more limited for winter forage than for corn. Planting configurations (narrow vs. wider row spacings) may also be involved. Olsen P was not measured beyond 30 cm in this study. The results suggest that winter forages, despite taking up less P than corn, play an inordinate role in lowering Olsen P from the first 30 cm and reducing the soil P most subject to runoff. This finding merits further study.

In summary, double cropping winter forages and silage corn increased total forage production in most years, appreciably increased P removal, and reduced Olsen P in the first 30 cm over that with corn alone. Winter forage–corn combinations did not always differ in production or P uptake, but winter triticale and corn resulted in the greatest P uptake and removal over 3 yr. Seeding rates of 168 kg ha–1 were frequently necessary for maximum boot stage forage production, but seeding rates did not appreciably affect P uptake.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
This is a publication of the Idaho Agricultural Experiment Station.

Received for publication September 1, 2005.


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





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