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© 2008 Plant Management Network.
Accepted for publication 11 September 2008. Published 3 November 2008.

Assessing Alternative Forage Production Systems for Organic Dairies in New England

John M. Jemison, Jr., Water Quality and Soils Specialist, University of Maine Cooperative Extension, Orono, ME

Corresponding author: John Jemison. jemison@maine.edu

Jemison, J. M. Jr. 2008. Assessing alternative forage production systems for organic dairies in New England. Online. Forage and Grazinglands doi:10.1094/FG-2008-1103-02-RS.

Abstract

Organic dairy farmers need high yielding, quality forages with low weed pressure. A four-year study was conducted in Maine to evaluate yield, quality and weed biomass of spring and winter small grains double cropped with brown midrib sorghum-sudan grass (SS). Double crops included spring barley/SS, winter barley/SS (WB/SS), winter triticale/SS (WT/SS), and winter wheat/SS (WW/SS). These were generally compared to organic open-pollinated corn silage grown adjacent to the study. Forage quality measures included crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), total digestible nutrients (TDN), and non-fiber carbohydrates (NFC). Corn was cultivated four times (two tine and two row cultivations); double crops received essentially no cultivation. Yield of WT/SS and WW/SS (10,710 and 9,695 lb/acre) was significantly higher than WB/SS or SB/SS (8590 and 7372 lb/acre) and were similar to corn silage (10,505 lb/acre). Double crop weed biomass was four times less (1 to 4% of DM yield) than corn (11.8% DM yield). Low manure N efficiency likely affected forage quality particularly CP, TDN, and NFC values. Significant nutrient yield differences (> 1200 lb/acre) were found between double crops, but corn NFC yield was almost twice that of any double crop. Supplementing high energy feeds can help balance double crop rations.

Introduction

Organic dairy production is one of the strongest growth areas of New England agriculture. As of 2007, northern New England had over 285 certified organic dairies, and more farms are transitioning to organic production methods. The first New England farms to convert to organic production methods were principally grass-based operations. As larger farms with more complicated cropping systems become certified, producing quality forages is increasingly challenging (3). Small grain cereals grown for silage have been a staple feed source for Canadian dairies (8), and they have been shown to be productive in Maine as well (T. Griffin, Tufts University, personal communication). When grown alone or as a double crop with warm season grasses or corn, growers need information to maximize forage yield and quality.

Weeds threaten the long-term sustainability of organic forage systems (5). Swanton and Weise (17) discussed the need for more systems-based research in organic forage production. Organic producers must rely on a variety of cropping systems and cultural weed control practices to manage weeds (5,15). Double crop systems that produce well during cool and warm periods should help growers maximize production in short season climates like New England while potentially reducing weed seed buildup, protecting the soil from erosion, and providing an early-season grazing source.

Feed is the single largest expense for organic dairies, with costs reported to be double the cost of conventional feed (9). Organic growers must maximize on-farm production of both energy and protein. While corn will be a part of many organic growers’ strategies, there is very little information available on the feed quality of alternative cropping systems, particularly those produced organically. Information on the yield, feed quality, and weed suppressive capacity of alternative cropping systems will help growers predict acreage needed, select specific cereals to grow, determine the need for cultivation, and predict herd response to these feeds. The objectives of this study were to: (i) assess yield and quality of spring barley and three winter grains double cropped with SS; (ii) assess effect of double crop strategies on weed biomass; and (iii) generally compare these systems to organic open pollinated silage corn.

Field Study Evaluating Double Crop Forage Systems

This study was conducted from 2004-2007 at the University of Maine Witter Center-Rogers Farm. Four double crop systems were evaluated in this work: SB/SS, WB/SS, WW/SS, and WT/SS. All small grains were planted with a grain drill at 125 lb/acre (desired goal to achieve approximately 25 to 30 plants/ft², a high rate recommended for organic growers to control weeds) to a 1.5-inch depth. Sorghum sudan grass was planted with a grain drill at 70 lb/acre to a one-inch depth as is recommended for organic production in Maine. Initially corn was included within the study design to directly compare yield, forage quality, and weed biomass with the double crop systems. However, in the first season, crows destroyed the corn planted within the study. Organic OP corn from an adjacent study evaluating intensity and frequency of corn cultivation methods was used for comparisons of yield, forage quality, and weed biomass. In 2005, the cultivation study was repeated, and it was again used for the source of comparative corn. In the final two years of the study, corn was planted next to the trial and weeds were controlled using the best methods found in the cultivation study. Replicate samples were collected from those plots in 2006 and 2007. We used OP corn in this work because our previous research has shown similar yields to hybrid corn of similar maturity in Maine and Vermont, and growers may save seed to reduce their production costs. Because corn was not grown within the study area, direct statistical comparisons between corn and double crop measures were not made, but the yield, quality, and weed biomass is included for general comparative purposes. Corn was planted at 26,000 seeds/acre; this is the recommended seeding rate for OP corn silage. Varieties used, planting and harvest dates for corn, and the double crop comparisons are presented in Table 1.

Table 1. Crop planting and harvest chronology from 2004-2007.

* Abbreviations: SB = spring barley;
WB = winter barley;
WW = winter wheat;
WT = winter triticale;
SS = brown midrib sorghum sudan grass.

Varieties: spring barley = Benefit;
winter barley variety = McGreggor;
winter triticale variety = TriCal 336;
winter wheat variety = Caledonia;
BMR sorghum sudan = Bovine Bounty;
corn = Wapsae Valley open pollinated.

Cropping sequence. To initiate the trial, the study area was planted to spring barley in May 2004 (Table 1). Following harvest, manure was applied and incorporated prior to planting SS. To allow maximum production, SS was harvested just before frost in October 2004. To ensure that winter grains were planted at the recommended time, the experiment was continued in a different organically certified field with similar soil type (well drained Melrose fine sandy loam) and fertility. The winter grains were double cropped with SS the following summer. To continue the second year of the spring grain double crop component, oats were planted with the winter grains with the expectation that they would winter kill. The following April (2005), manure was spread over the dead oat residue and incorporated prior to planting spring barley. The experiment continued to be rotated between these two fields in a similar manner for the remainder of the study.

Harvest and analysis. Yield, forage quality measures including crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), total digestible nutrients (TDN), and non-fiber carbohydrates (NFC), and weed biomass were measured for all double crop systems and corn silage. Forage quality yield (quality parameter multiplied by dry matter yield) was determined for the various forage quality measures to provide estimates of double crop and corn nutrient yield. Small grains yield estimates were taken at the soft dough stage to maximize silage yield and energy content. Two 5.2-ft² plots were cut at the ground surface from each 300-ft² plot, combined, dried, weighed, and ground for analysis. The SS plots were harvested to maximize quality at approximately 40 inches in height (12). Samples were processed similarly to the small grains. Corn silage yields were collected by cutting two 16.4-ft rows per plot. Eight whole plants were chopped with a chipper-shredder; a subsample was collected, dried, weighed, and ground for feed quality analysis. To evaluate forage quality of the various double crop systems, a weighted average forage quality yield was calculated for small grains and SS.

Weed management. The principle weeds in the study areas were lambsquarters (Chenopodium album), red root pigweed (Amaranthus retroflexus), and shepherd’s purse (Capsella bursa-pastoris), green and yellow foxtail (Setaria sp.), barnyard grass (Echinocloa crus-galli), and some quackgrass (Agropyrons repens). The corn weed management plan included two tine cultivations (one tine cultivation within a week of planting and a second one at first leaf stage) and two row cultivations at the third and sixth leaf stage. Spring barley was tine cultivated once in 2004 when the crop was two to three inches tall. No further cultivations were made in the double crop systems. We estimated weed biomass at crop harvest by measuring the weeds collected in the two 5.2-ft² small grain and SS harvest samples from each plot. The same methods were used as with the corn. Following separation of weeds from crop biomass, plants were dried at 150°F, weighed, and weed biomass was expressed as a percentage of the total crop yield. Weighted average weed biomass was calculated for each double crop system.

Nutrient management. Crops were fertilized using solid dairy manure where N content ranged from 7 to 10 lb total N, 0.3 to 2.2 lb of NH₄-N, and 5.6 to 9 lb organic N per ton. Manure P₂O₅ and K₂O ranged from 4.2 to 6 and 7.8 to 15 lb/ton, respectively. Manure application rate, total and estimated available N, are presented in Table 2. Estimates of available N from manure applied to corn were based on 90% of the NH₄-N + 35% of the organic N being available (13). Manure N availability for small grains and SS was more difficult to predict. While estimates for manure N availability in full season small grains have been as high as 40% (D. Beegle, Penn State University, personal communication), there is little information on manure N availability for small grain silage or SS. We estimated our available manure N to be between 25 to 40% of the total N content of the manure. Our intent was to model practices of typical Maine organic dairy farms and attempt to meet the N demand of each crop with manure. In the first two years, solid dairy manure was sourced directly from the manure pit; in the latter two, manure was stockpiled at the farm during the late winter and applied and incorporated prior to planting. This may explain the low manure NH₄-N content.

Table 2. Manure application and estimated availability to subsequent crop.

 ^w SS = brown midrib sorghum sudan grass.

 ^x corn manure N availability calculated by taking 35% of organic N + NH₄-N.

 ^y winter and spring grain manure N availability estimated to be 25% of total N.

 ^z SS manure N availability estimated at 25% total N.

Experimental design and statistical analysis. The double crop systems were laid out in a randomized complete block design with four replications. All data collected for the double crop systems (dry matter yields, various measures of forage quality, forage quality yield, and weed biomass) were analyzed using the PROC GLM routine in SAS statistical software (SAS Institute Inc., Cary, NC). Factors analyzed included cropping system and season (year) and cropping system by season interaction. Means were separated using Fisher’s LSD.

Cropping System Yields

Double crop dry matter (DM) yields were strongly influenced by the environmental conditions found during the study period (Table 3). Despite a cool wet spring that caused delayed spring barley planting in 2005, warmer than average temperatures and timely rains created excellent growing conditions for winter grains, SS, and corn. In contrast, the 2004 and 2007 seasons were some of the least favorable for SS and corn as monthly average temperatures were below long-term averages. In these seasons, the WT/SS and WW/SS double crops yielded 1900 and 1150 lb DM/acre more than corn. Annual environmental variations and the complete loss of winter barley in 2006 led to a significant cropping system by year interaction. The complete loss of winter barley, the significant damage to winter wheat, and to some extent, triticale by an extended period of ice cover in 2006 shows some of the risks of growing winter grains in northern New England. The potential benefit of winter barley compared to winter wheat or triticale is that it reaches soft dough as much as two weeks before triticale or wheat, and produces high quality forage (Tables 1 and 4). Earlier harvest potentially allows earlier SS planting, and improves the chance of taking two cuts. However, the risk of winter kill is the highest among the winter grains evaluated here. Also, despite the earlier planting, SS yield was not influenced by the additional two weeks of growth when planted after winter barley. Of the three winter grain double crop systems, the three-year average yield of WT/SS was between 1000 and 3300 lb/acre higher than any other double crop combination. The WT/SS double crop produced yields similar to silage corn, and the improved winter hardiness likely made this the most favorable winter grain in a cool, wet, short-season production area like Maine. However, with an average yield of 9695 lb/acre, WW/SS yielded similarly to WT/SS. A potential advantage of winter wheat is the option to harvest mature grain for the organic flour market.

Table 3. Monthly average temperatures, T (given in °F), and total monthly precipitation, ppt (given in inches), during 2004-2007 in Maine 2 W-Rogers Farm, Old Town, ME.

Source: www.ncdc.noaa.gov.

In general, SS yields were influenced by accumulated heat units and timely moisture. It was possible to harvest SS twice within the growing season in two of three years following winter small grains and once following spring barley. Dry matter yields of SS were consistently about half of the total double crop yield (Fig. 1). The risk of growing a warm season grass like SS is the need for heat for productivity and dry weather for forage harvest. We found significantly lower production in 2004 and 2007.

Fig. 1. Double crop and silage corn mean dry matter yields.

The highest double crop DM yields presented here are in some cases half that of small grain yields reported in previous research (6,8). The low NH₄-N content of the manure used in this study (Table 2), and the relatively low protein content of both the double crop combinations and corn suggest that N availability likely limited yield and affected forage quality. The higher soft dough stage cereal yields reported by Juskiw et al. (8) and Acosta et al. (1) may have been aided by the fact that they used spring fertilizer N in a conventional production system. Like most warm season grasses, SS responds well to available N, and yield also appeared to be limited by N. If available, an application of liquid manure in the spring could improve N availability to winter grains, but there is a risk of increasing soil P to unacceptable levels. Using the P removal estimates developed by Ketterings et al. (10), less than 60 lb P₂O₅ were removed by our average SS yields. In this work, over 100 lb P₂O₅ per acre were applied; if done on a farm scale, two applications of manure per year at these rates would likely increase soil P. Steps taken to maximize NH₄-N availability to the crop (rapid incorporation of manure and no stacking solid manure on site over winter), or appropriate use of green manure crops in combination with manure may serve to boost organic double crop production yields (14).

Weed Biomass

Weed biomass in this study was affected differentially by cropping system and year. The winter-killed small grains allowed space for weeds, particularly in 2006. Since triticale had the least winter kill, it had the lowest three year average weed biomass at 1.7% of dry matter yield compared to 3.8% for winter barley. Given the size of triticale, it appeared to be more competitive with weeds than winter barley or winter wheat. Narrow row spacing, high seeding rate, and altered timing of crop planting to miss the major flush of annual weeds all combined to keep weed pressure low in these double crop systems. Conversely, weed biomass varied from 4.5 to 24.5% of total production over the four years in intensively cultivated corn. Timely cultivation is essential in field corn. Wet soils prevented timely cultivation particularly in 2004 and 2005. The best corn weed control (4.5 and 5.8% of DM yield) was found in 2006 and 2007; soil moisture was optimum for cultivation in those years. Given the cool wet springs found in northern New England, effective weed control with organic corn production is a challenge. Double crop systems offer organic growers the chance to reduce weed pressure and may slow the buildup of weeds, particularly in seasons with difficult environmental conditions.

Forage Quality Content and Yield of Corn Silage and Double Crop Combinations

Forage quality measurements for the spring and winter grain double crop combinations and corn are presented in Table 4. For most forage quality measures, there were significant cropping system by year interactions. The seasonal environmental variability likely influenced production of starch and other plant components that influence forage quality. There was no significant difference in the protein concentration of winter and spring double crop systems (Table 4). All were slightly higher than corn. Protein concentrations of the small grain silages in this study were similar to those reported by Juskiw et al. (8). It is widely recognized that plant protein decreases and fiber content increases with advancing stage of development. Growers should make small grain harvest decisions based on what forage component they need the most (energy or protein) (17). The protein yield was influenced by dry matter yield as the WT/SS double crop produced 70 lb protein yield/acre more than winter barley and 50 lb/acre more than WW/SS and SB/SS (Fig. 2). Of the double crop systems evaluated, the 10 to 15% lower NDF and 8 to 11% lower ADF values for WB/SS indicated significantly higher quality forage than the other double crop systems and indicate an increased likelihood of greater forage intake and potentially higher milk production (7).

Table 4. Double crop forage quality analysis averaged across seasons.

* SB/SS = spring barley/sorghum sudan grass double crop;

  WB/SS = winter barley/sorghum sudan grass double crop;

  WT/SS = winter triticale/sorghum sudan grass double crop;

  WW/SS = winter wheat/sorghum sudan grass double crop.

Fig. 2. Cropping system forage quality yield.

The NDF and ADF values for WB/SS were roughly equivalent to that of corn. However, the lower yield of WB/SS and the higher risk of winter kill make the higher forage quality benefit of this double crop risky. The WW/SS system had between 2 and 4.2% higher nonfiber carbohydrate (NFC) content than the other double crop combinations. A higher energy forage could be important for an organic grower with limited corn availability. However, WW/SS was only significantly higher than WB/SS for total digestible nutrients (TDN). Given the high DM yield of WW/SS and WT/SS, the TDN and NFC yields were between 400 and 600 lb/acre greater than those for the WB/SS and SB/SS systems (Fig. 2).

Forage quality and yield measures were also made for the OP silage corn. Corn protein and corn protein yield were roughly similar to the double crop systems. The difference between any double crop systems and corn was the high NFC yield; corn had nearly twice the NFC yield compared to any double crop combination (Fig. 2). For this reason, corn will likely remain an important component in organic dairy rations.

The protein content of the SS component of the double crop systems averaged around 10.6% (data not presented). Ketterings et al. (11) found between 6.1 and 10.2% crude protein in plots receiving no additional N at the six locations over three years, and only one site had a history of manure. They further reported an economic optimum N (EON) rate of between 122 and 171 lb/acre in a two cut system, and Bayaert and Roy (2) reported an EON of 74 to 95 lb N per acre in a three cut system. If the estimates of manure-N availability presented in this work of 30 to 60 lb N per acre are accurate, N very likely limited SS yield. However, it is difficult to compare organic and conventional production systems, and the planting times in those studies were weeks earlier than those used here. However, the low SS yields and protein content found in these studies illustrate some of the difficulties that organic growers frequently have meeting crop N needs using only manure. Use of plowed down cover crops may also help boost N availability. Organic growers that use the best methods of manure storage, application, and timely incorporation may improve forage protein and overall competitiveness (14).

While the WB/SS system appeared to have the highest intake potential of the double crop systems evaluated, the high NFC and TDN yield and improved potential for winter survival likely make the WT/SS double crop the best option for organic dairy producers looking for quality forages with low weed pressure. No single double crop combination excelled in all measures of forage quality or forage quality yield. For example, WT/SS had high NDF and ADF values (low forage intake potential), but the high TDN yield indicated that the system can produce a high TDN ration, almost as high as corn. However, the NFC yield of all the double crop systems was approximately half that found for silage corn. Unless another energy source were available (for example grain corn or another high starch feed source), it would be difficult for most producers to completely replace corn silage with any of these double crop systems and maintain milk production. However, weeds can also lower forage quality. Generally by harvest, weeds in a corn silage system are mature with a high fiber content which could lower forage energy and reduce quality. Weeds in a double crop system would be comparatively younger and possibly more palatable at each harvest. This could be particularly important in years like 2004 when the weed biomass made up a quarter of the total corn silage biomass.

Conclusions

The double crop systems evaluated in these studies offer organic dairy producers a means to produce forages that yield similarly to organically produced OP corn and provide an effective, ecological approach to manage weeds. Fall grains provide an opportunity to break summer annual weed seed buildup, and the weeds that do germinate are harvested well before they become overly fibrous and unpalatable. The double crop forage quality is generally not as high as that of corn, particularly forage energy. Growers who select these systems should balance the double crop forage with other higher energy feeds to maximize milk production.

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