Intercropping Tropical Vine Legumes and Maize for ... - PubAg - USDA

Intercropping Tropical Vine Legumes and Maize for Silage in Temperate Climates Heathcliffe Riday Kenneth A. Albrecht

ABSTRACT. Maize silage is used extensively in American dairy rations. Increasing protein content would enhance maize silage quality. This study examined nine forage legume species (Austrian winter pea, common bean, cowpea, lablab, scarlet runner bean, sesbania, sunn hemp, tropical kudzu, and velvet bean) grown in mixture with maize plants in Wisconsin, in the U.S. Plants were evaluated for growth throughout the growing season, harvest forage dry matter content, total dry matter yield, and forage mixture components. Of the forage legumes tested, common bean, lablab, scarlet runner bean, sunn hemp, and velvet bean were most successfully intercropped with maize. The common bean entry was the most aggressive forage legume, comprising 23% on a dry-matter basis of the final harvested forage mixture. The lablab entry, despite a slow start, became more productive during the late growing season and comprised 7.4% on a dry-matter basis of the final harvested forage mixture. Harvested forage moisture ranged from 299 g kg -1 to 364 g kg of dry matter. Ecept for the common bean mixture, whictf had a lower forage dry-matter yield, the mixtures did not differ from one another or the pure maize control for dry-matter accumulation per unit area. Similar to forage dry-matter yields, stover forage mixture fractions were not significantly different among entries, except for

• Heathcliffe Riday is affiliated with the U.S. Dairy Forage ResearchCenter (USDA-ARS), 1925 Linden Drive West, Madison, WI 53706 (E-mail: , riday@ wisc.edu ). Kenneth A. Albrecht is affiliated with the Agronomy Depailment, University of Wisconsin-Madison, 242 Moore Hall-Agronomy, 1575 Linden Drive, Madison, WI 53706 (E-mail: kaalbrec @facstaff.wisc.edu ). Address correspondence to: Heathcliffe Riday at the above address. Journal of Sustainable Agriculture, Vol. 32(3) 2008 Available online at http://www.haworthpress.com © 2008 by The Haworth Press. All rights reserved. doi:10. 1080/10440040802257280

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the common bean-maize mixture. Grain yields were inversely proportional to the amount of legume present. KEYWORDS. Maize silage. intercropping, tropical forage legumes, biomass, moisture, growth rate

INTRODUCTION A major proportion of U.S. Midwestern dairy cow rations is maize silage (Zea mays) (Grande et al., 2005). Some advantages of maize silage include increased dry matter yields per hectare (13 to20 Mg ha), high energy concentrations, ease of ensuing, and uniformity of silage (Allen et al., 2003). One weakness of maize silage is lower protein levels as compared with forage legumes. Because of this, maize silage is often fed with forage legumes high in protein, such as alfalfa. lntercropping maize and forage legumes offer an alternative means of increasing silage protein content. .. In temperate climates numerous studies have examined intércropping annual legumes such as soybean (Glycine max) with maize (Crookston and Hill, 1979; Herbert et at., 1984; Martin et al., 1990). The earliest maize-soybean mixture studies date back to the I 920s (Crookston and Hill, 1979; Hebert e(al., 1984). Various forage legumes, such as alfalfa (Medicago sativa), red clover (Trifoliuni pratense), kura clover (Trifoliu,n angibuum), and lupins (Lupinus), have also been used in combination with maize in temperate climates (Eberlein et al., 1992; Prithiviraj et al., 2000; Affeldt et al., 2004; and.Graber and Massengill, 2005). However, these temperate forage legumes are low growing (i.e., less than 1 meter in height) relative to maize plants. This situation forces the legumes to grow under the maize canopy, which intercepts 95% or more of photosynthetically active radiation in typical 75 cm maize row spacing and 75,000 plants per hctare maize densities (Nafziger, 2002). One wayj researchers have attempted to mitigate light competition in maize-forage intercropping systems is by using different row spacings (Crockston and Hill, 1979; Herbert et al., 1984; Redfearn et al., 1999; and Polthanee and Treld-ges, 2003). For example, one maize-soybean intercropping study found the most favorable soybean yields at wider maize row spacings (Mohta and De, 1980). Another means to Potentially optimize forage productioti in a temperate climate maize-legume

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intercropping system is to utilize more aggressive tropical forage legumes, which grow taller than temperate forage legumes and which have the ability to climb other plants to reach sunlight. In many tropical areas there is a long cultural tradition of intercropping maize with vine legumes, especially on smaller farms (Piper and Morse, 1922; Schaaffliausen, 1963; Solomon and Flores, 1994; Maasdorp and Titerton, 1997; Polthanee and Trelo-ges, 2003). Traditionally indigenous groups in Central America have intercropped maize and scarlet runner beans (Phaseolus coccineus) (Solomon and Flores, 1994). Sometimes common bean (Phaseolus vulgarius) and squash are included in such intercropping schemes (Almador, 1980; Solomon and Flores, 1994). In these traditional Mesoamerican planting arrangements, seed is planted in hills, allowing light to reach all species. Such polycultures work well when crops are hand harvested. However, hill planting schemes are less conducive for use in intensive mechanized agriculture. Nevertheless, many examples of mechanized maize-vine legume intercropping in the tropics have been documented. In Brazil, lablab (Lablab purpureus) and maize have been intercropped (Schaaffhausen, 1963). In Zimbabwe and South Africa, velvet bean (Mucuna pruriens) is intercropped with maize to produce dairy feed (Maasdorp and Titterton, 1997; Maasdorp et al., 2000). In the early 20di century, there are reports from the southern U.S. of maize-velvet bean intercropping as well (Piper, 1918; Eilittä and Sollenberger, 2000). However, no studies have examined tropical vine legumes grown with maize in temperate climates. One problem in transferring tropical maize-legume intercropping systems to temperate climates is the shorter growing season. In many existent tropical maize-legume intercropping systems the maize is harvested first for grain s'ith the legume component harvested later (Schaaffhausen, 1963; Solomon and. Flores, 1994). For example, when lablab is intercropped with maize, the maizegrain is harvested first, freeing lablab from competition, thereby allowing the lablab to grow and entangl the haie stubble. Later ihis'maize 1 'iubble-legu'rne mixture is harvested for silage. Suchstems would be similar to perennial legume grain cropping systems used ii - temperate areas where small-seeded legumes are established with a small grain', with the,'g'ral harvested in autumn and the small seeded-legume becoming t mature stand the following spring Another potential problem of introducing tropical legumes to temperate growing areas is their adaptability to tethperate envionmental towing conditions, such as cooler soil and air temperatués during the growing season and longer summer day lengths.

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The objective of this study was to test various tropical vine legumes (common bean, cowpea, lablab, scarlet runner bean, tropical kudzu, and velvet bean) and tall-growing legumes (Austrian winter èa, lathco flatpea, sesbania, and sunn hemp) and determine competitive ability in mixture with commercial maize hybrids for silage in a temperate growing environment. Successful annual legume species would need to establish rapidly and be competitive enough to grow through a developing maize canopy, but without outcompeting the maize plants. To ascertain differences among legume species in the maize-legume mixtures, the following were measured: species mixture component fractions, biomass yield, harvest forage moisture, and plant height throughout the growing season.

MATERIALS AND METHODS Species The following eight tropical forage legume species were used in this study: common bean (cv. 'Genuine Maize Bean ! ), cowpea (cv. 'Catjang', cv. 'Ironclay', and cv. 'Reseeding Type'), lablab (probably cv. 'Rongai'), lathco flatpea, sesbania, scarlet runner bean (probably cv. 'Scarlet Emperor'), sunn hemp (cv. 'Tropical Sun'), tropical kudzu, and velvet bean (unknown [tiger striped brown-white seed], unknown [white seed], and cv. 'Georgia Bush' [white seed]) (Table 1). Austrian winter pea was included to represent a lower-growing cover crop species.

Experimental Design and Planting Fifteen entries were included in the experimnt; 14 were maize-legume mixtures, and F was a pure, maize control. Three replicates of each entry were grown in a randomized , complete block design at the Agricultural Research Station at Arlington, WI (43°18'N, 89°21'W) in a Piano silt loam (fine-silty, mixed, superactive, mesic typic argiudolls) and at the U.S. Dairy Forage Research Center Dairy at Prairie du Sac, WI (43°19'N, 89°44'W) in Richwood silt loam (fine-silty, mixed, superactive, mesic typic argiudolls) for a total of 84 plots. At Arlington, on 4 May 2004, Dekalb 'DKC 50-20' round-up ready maize (100 RM) was planted at 75,000 plants per hectare, in 75 cm rows. At Prairie du Sac, on 5 May 2004, Coltenberg 'K46666 RR' round-up ready maize (96 RM) was planted at 75,000 plants per hectare, in 75 cm rows. Maize was planted using standard mechanical planting equipment. Legumes were planted at

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Arlington on 18 May 2004 and Prairie du Sac on 19 May 2004. After inoculating legume seeds with the appropriate rhizobium species, legume seeds were hand planted into 5 cm furrows and covered. Legume planting densities varied based on seed size and recommendations (Table 1). Each mixture plot consisted of two legume rows planted between two maize rows, with a legume row spaced 15 cm from one maize row and the legume rows spaced 45 cm from one another (Figure 1). Plots were 4 m long and had a maize row border on either side. The maize control plots were the same as the maize-legume mixture plots without the legume component. Measurements and Harvest During the first 3 weeks after legume planting, seedling emergence was scored as presence or absence of emerged legume seedlings in a plot. FIGURE 1. Maize-legume intercropping plot layout planted at two Wisconsin locations in 2004.

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Weekly height measurements of each plot were taken throughout the growing season by averaging 5 height measurements per plot per week. Plots were harvested 20 September 2004 at Arlington and 22 September 2004 at Prairie du Sac. Two whole plant maize-legume mixture subsampIes were taken from each plot, one from each of the two maize-legume rows in each plot (Figure 1). Each whole plant subsample was obtained by handharvesting all plants in a I m length of maize row. A small pure legume subsample was taken from each plot and weighed wet. After subsampling, whole plots were hand harvested, chopped using a wood chipper, and weighed wet. Two chopped subsamples per plot were taken and weighed wet. All plot subsamples including whole plant maizelegume, pure legume, and chopped maize-legume, were dried at 60°C in a forced-air dryer and weighed dry. Dried whole plant maize-legume subsamples were hand separated into legume stem, legume leaf, legume pod, maize stover, and maize grain components. Each component was weighed.

Data Analysis The PROC GLM feature of SAS statistical soft ware package was used to estimate entry effects and least significant differences (SAS, 1999). For analysis purposes, entries and locations were treated as fixed effects and replications as random effects. Pearson correlation coefficients were calculated using PROC CORR in SAS.

RESULTS Germination and Pre-Canopy Closure Differences in germination speed weie observed after legume planting. The most rapid rd species to emerge were Aiistnan winter pea cowpea lablab, and sunn hemj'(Table' I). Many of the rapidly emerging species' had 100% sëèdling emergence one week after planting. The slowest emerging species were Iathco flat pea, sesbania, and velvet bean (Table 1). Most of these species did not reach 100% emergence until the fourth week after legume planting. 'During the early growing season we noted that the lathco flatpea, sesbania, and tropical kudzu entries failed to thrive; throughout the growing season none of these species grew taller than 30 cm. Of the three velvet bean entries grown in this study, we noted that the two white seeded entries had

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FIGURE 2. Maize and legume plant heights (cm) averaged over two Wisconsin locations in 2004. 300 250 200 150 100 50 0

1-May-04

3-Jun-04 6-Jul-04 8-Aug-04 10-Sep-04 Time (days)

- - - Common Bean - - Lablab Sunn Hemp -. -. Velvet Bean

S. Runner Bean Pure Maize

poor field germination. In contrast, the tiger-striped brown-white seeded entry had good germination. After seedlings had emerged in May we observed that the scarlet runner beans and common beans grew most rapidly through mid-July (Figure 2). Post-Canopy Closure The maize canopy closed in mid-July after the maize plants had grown 2 m tall, which dramatically slowed the legume growth (Figure 2). Under the canopy a dark moist environment existed, which produced legume plants with more elongated stems typical of plants in such light deficient conditions. Legume entries that had not reached approximately one meter in height by this time point failed to produce significant biomass by harvest time (Table 1). The non-trailing entries such as 'Catjang' cowpea and 'Georgia Bush' velvet bean especially suffered under the canopy and were unable to reach the light. Sunn hemp, a non-trailing legume, on the other hand, grew tall enough to reach the light. Although the two trailing cowpea entries 'iron clay' and 'Reseeding' appeared very healthy, their

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smaller plant size did not make them appear worthwhile for use in an intercropping system. At the time of canopy-closure, powdery mildew killed the Austrian winter peas and infected many scarlet runner bean plants. Additionally, scarlet runner bean growth was stunted, due to infestation with potato leafhoppers (Enipoascafabae). Leafhopper and powdery mildew damage were much more prevalent at the Arlington field location. A few velvet bean vines had an unidentified stem rot, which killed the stem above the point of infection. The lablab and common bean, in contrast, displayed no signs of chlorosis or disease. When maize plants reached their maximum height of 3 m and initiated pollen shed around July only five legume entries of interest remained: lablab, common bean ('Genuine Corn Bean'), scarlet runner bean, sunn hemp, and tiger-striped seeded velvet bean (Figure 2). The most aggressive legume was the common bean, which was not far behind maize growth; the common bean was so aggressive that we observed broken maize stalks above the maize ears by August 5. The scarlet runner bean, on the other hand, which initially was the fastest growing legume, began to flower shortly after mid-July, which slowed its plant growth (Figure 2). The early flowering did, however, produce large scarlet runner bean pods by August 161h By mid August the common bean had grown so profusely that the vines created a matted living surface about 1 .5 m off the ground, and maize stalk breakage above this point due to vine weight was common. By August 26' the common beans reached full flower. It was around this time point that we observed an acceleration in lablab growth (Figure 2). The accelerated lablab growth became more apparent by early September as the maize plants began to dry down and shrink (Figure 2). The maize dry-down opened up the maize canopy allowing the legumes more light. The species that had not yet flowered, particularly the lablab and velvet bean, benefited from the increased light (Figure 2). A few flowers were observed on sunn hemp and velvet bean by September 1. By September 10, even a few velvet bean pods were observed. No flowers were ever observed on the lablab plants. At harvest time in the later part of September the common bean-maize plots looked vines overtaking had completely covered maize plants in many plots. Many of the maize-lablab plots also looked impressive. Of the scarlet runner bean plots undamaged by mold and leafhoppers, the remaining plants had overgrown their maize companion.

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Harvested Material After visually assessing the plots, we determined that the lablab, common bean, scarlet runner bean, sunn hemp, and velvet bean (tiger-striped seed) entries had sufficient legume material to be significantly different from the pure maize control. Therefore, we only harvested and further analyzed these plots. Because we envisioned this intercropped material for use as silage, we were concerned that the high moisture of the legumes would shift the overall chopped forage out of the recommended 350 g kg' dry matter content (DM) maize silage range (Allen et al, 2003). Therefore, the plots were harvested at about 3/4 milk line as opposed to the recommended 1/2 milk line (Allen et al., 2003). All mixtures, except the common bean (299 g kg' DM), were not significantly different from the recommended 350 g kg -1 DM target for maize silage (Table 2). Legune DM ranged from 130 g kg to 178 g kg with lablab having the lowest DM and sunn hemp having the highest legume DM (Table 2). The maize in the different mixtures had a large range of DM levels from 375 g kg' with sunn hemp to 540 g kg with common bean. The mixtures with the most aggressive legumes had maize companions with the highest DM. Plot observations during harvest revealed more dead maize material (i.e., brokn stalks and leaves) in plots that had the most aggressive legumes. In extreme cases the actively growing legumes had completely buried the maize, which in turn were completely dead. There werg no differences among plots for total dry matter yield, except the common bean-maize mixture, which had a slightly lower - TABLE 2. Maize-legume intercropped silage mixture

• dry matter content (g kg -1 ) measured at two Wisconsin, USA locations in 2004 at harvest Mixture

Total -

Component

g kg-1 Maize Legume gkg'

Common Bean Lablab S. Runner Bean Sunn Hemp Velvet Bean Pure Maize LSD (0.05)

299 540 145 356 421 130 345 382 133 363 375 178 361 384 151 364 364 29 119 21

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TABLE 3. Maize-legume intercropped silage mixture dry matter yield (Mg ha-1 ), maize component (stover and grain) g kg -1 , and legume component (leaves, stems, pods) g kg measured at two Wisconsin locations in 2004 at harvest Mixture

Total Yield Maize Mg ha Stover Grain

Legumes Total Stems Leaves Pods g kg-1

Common Bean Lablab S. Runner Bean Sunn Hemp Velvet Bean Pure Maize LSD (0.05)

20.9 426 340 23.0 442 485 24.3 443 496 23.4 445 517 23.2 449 522 23.6 464 536 2.0 29 47

234 65 74 37 61 20 29 15 38 20

73 97 35 0 25 15 10 2 22 0

97 27

24 29

yield than the other entries (Table 3). Despite the similarity in dry-matter yield per unit area, there were significant differences in dry-matter mixture constituents. Common bean-maize mixtures had the highest legume proportion at 234 g kg', followed by lablab, scarlet runner bean, velvet bean, and sunn hemp mixtures (Table 3). Increased legume content in the mixtures was inversely proportional to decreased grain yields (r = —0.99; p