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PRODUCTION PAPERS

Red Clover–Potato Cultivar Combinations for Improved Potato Yield

^a Prince Edward Island Dep. of Agric. and Forestry, P.O. Box 1600, Charlottetown, PE, Canada C1A 7N3
^b Agric. and Agri-Food Can., Crops and Livestock Res. Cent., 440 University Ave., Charlottetown, PE, Canada C1A 4N6

^* Corresponding author (avsturz{at}gov.pe.ca).

Received for publication May 30, 2002.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
One of the challenges to potato (Solanum tuberosum L.) production systems is to reduce N applications without incurring any marketable yield penalty. From previous studies, it was established that red clover (Trifolium pratense L.) can encourage the development of beneficial rhizobacterial communities that promote potato growth and development, in essence making agricultural soils as or more productive for specific quality attributes. In the present 2-yr study, we examined the influence of the red clover cultivars AC Charlie, AC Endure, AC Kingston, Atlas, Marino, and Prosper on the potato cultivars Kennebec, Russet Burbank, and Shepody, grown in the following season. We found that the preceding clover cultivar had no influence on either Kennebec or Russet Burbank. However, Shepody potato following AC Kingston showed a significant yield advantage (P = 0.05), in tonnes per hectare, over other clover cultivars (except Atlas) in the Size 2 category of tubers (tubers >51 mm in diam. and <280 g), the grade for which growers are characteristically paid the most. We encourage breeding programs to examine the ability of any given line to manipulate its root zone microflora with respect to its own needs and to those of subsequent crops. While the complexities of plant–soil–microbial interactions are great, the beneficial biological interactions that stimulate crop yields and improve plant health can be evaluated relatively simply, and general management strategies can be devised accordingly for any given set of crop combinations and growing environments.

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
IT IS COMMONLY HELD that the principal benefits of including a clover crop in a rotation sequence are the residual N left in the soil and the organic matter added (Bruulsema and Christie 1987; Christie et al., 1992). However, it is also recognized that field crop history (Glandorf et al., 1993; Leyns et al., 1990) and cultivar selection (Chanway et al., 1988) can stimulate specific beneficial bacterial populations in the root zone that may also lead to improvements in soil fertility, crop vigor, and yield.

Along the northeastern seaboard of Canada and the USA, potato is often grown in a 3-yr crop sequence of potato, barley (Hordeum vulgare L.) underseeded with red clover, and red clover (Bernard et al., 1993). Clover plowdown in the third year is preparatory to potato planting. Sturz and Christie (1995)(1999) showed that potato growth can benefit from specific rhizobacterial communities encouraged to develop in complementary rotational crops, such as clover.

In clover (Sturz and Christie, 1995; Sturz et al., 1997) and potato (Sturz, 1995), rhizobacteria are known to be able to promote or depress plant growth and development in their respective plant hosts. When plant–bacterial populations are complementary, the host and its resident rhizobacteria appear to benefit (Bakker and Schippers, 1987; Kloepper et al., 1980). However, so-called deleterious rhizobacteria may develop occasionally and suppress plant growth (Frederickson and Elliott, 1985; Schippers et al., 1987) in the absence of any direct phytopathogenic effects or physical soil properties. Such noncomplementary microflora can result in an inhibitory allelopathic growth effect. For example, in clover–maize (Zea mays L.) rotations, clover plowdown and the subsequent decomposition of clover plant tissue results in the release of resident endophytic bacteria back into the soil, inhibiting the rate of emergence and growth of any subsequently planted maize crop (Sturz and Christie, 1996).

By virtue of their adaptability and versatility, rhizobacteria are a key agent of change in soil agroecosystems. As beneficials, potato rhizobacteria appear able to exert a profound influence on potato crop health and yield characteristics, including tuber number, tuber size, and disease resistance (Sturz, 1995; Sturz and Matheson 1996).

To avoid colonization by harmful microorganisms in the root zone, plants have developed a number of strategies. They appear able to engineer the composition of the microbial community around their root systems through the exudation of specific carbohydrates, carboxylic and amino acids (Hawes et al., 1998; Grayston et al., 1998), to foster the development of beneficial rhizobacterial communities. Host–rhizobacterial relationships are so intimate that the composition of rhizomicrobial communities can be cultivar specific (Chanway et al., 1991; Siciliano et al., 1998).

Rhizobacteria can themselves elicit root exudation responses in host plants, so encouraging the plant host to sustain that specific rhizobacterial community in the root zone (Parmar and Dardarwal, 1999). In return, root zone bacteria can generate a wide array of secondary metabolites that can have a positive influence on plant growth (Patten and Glick, 1996), so enhancing the availability of minerals and nutrients (Murty and Ladha, 1988; Wang et al., 1993), improving N fixation ability (Ladha et al., 1997), decreasing susceptibility to frost damage (Xu et al., 1998), improving plant health through the biocontrol of phytopathogens (Weller, 1988), inducing systemic plant disease resistance (Van Loon et al., 1998), and facilitating plant establishment, growth, and development (Lazarovits and Nowak, 1997).

Preliminary greenhouse studies have demonstrated that one mechanism by which such growth promotional effects occur is through the stimulation of root endophyte bacteria from specific clover cultivars that are capable of improving growth in succeeding potato cultivars (Sturz and Christie, 1998). For example, the potato cultivar Russet Burbank performed best with root zone bacteria sourced from the red clover cultivar Marino while Shepody performed best with bacteria from ‘Altaswede’ root zones (Sturz and Christie, 1999). These findings suggested that the development of beneficial microfloral communities within the roots and in the surrounding root zone soils of potato crops can be used to reduce genotype x environment interactions and increase stability in growth characteristics over years and locations.

One of the challenges to contemporary potato production systems is to maximize any such beneficial microbial allelopathies in successive crop rotations, with a view to reducing current N requirements without incurring any yield penalty and, where possible, improving marketable yield. Current concerns surrounding contamination of ground and surface water by fertilizers have emerged as a significant human health and environmental issue for agriculture, especially in North America (Agric. and Agri-Food Can., 1997; Royal Commission on Agric., 1997). The present study examined the feasibility of enhancing the fertility of field soils by selecting complementary cultivars in crop rotations that foster the development of beneficial microbial root zone communities, resulting in agricultural soils as or more productive for specific quality attributes, with a reduced reliance on conventional levels of artificial N amendment.

We provide further information to show how cultivar-specific red clover–potato selections promote yield benefits, improve product quality, and stabilize marketable yields in potato field production.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
The experiment was performed at the Harrington Research Farm, Prince Edward Island (PE), Canada, from 1997 to 2000. Seedbed preparation was in May of each year when the soil was moldboard-plowed to a depth of approximately 20 cm, disced at least once to 15-cm depth, and harrowed to 15-cm depth. The soil at Harrington is an Orthic Humo-Ferric Podzol (Orthic Podzol in FAO classification) Charlottetown fine sandy loam, developed on acidic glacial till parent material. The particle size distribution of the Ap horizon (0–30 cm) was as follows: 8% clay ( <2 µm), 30% silt (2–50 µm), 40% fine sand (50–250 µm), and 22% medium and coarse sand.

Potato was planted in the third year of a three-crop sequence following barley (‘Chapais’) and red clover. Six clover cultivars (AC Charlie, AC Endure, AC Kingston, Atlas, Marino, and Prosper) were seeded in a randomized complete block design with four replications. Clover plots were 6 by 10 m. In the following spring, the clover plots were plowed, and potato was planted in single rows within each red clover plot (split plot). Three cultivars of potato were tested, namely Kennebec, Russet Burbank, and Shepody. Seed potato (cut-seed pieces, 42–56 g) was sown in single rows, 7.6 m long with 0.9 m between rows and a 3-m headland between replications to reduce the possibility of transferring material from one replication to another, during tillage operations. In-row seed piece spacings were 25 cm for Kennebec and Shepody and 38 cm for Russet Burbank. Potassium (K₂O) and P (P₂O₅) fertilizers were applied at 168 kg ha^-1 as recommended. All plots received 112 kg ha^-1 N fertilizer. This is the recommended rate for Kennebec and Shepody following clover whereas that for Russet Burbank is 151 kg ha^-1. The usual recommended rates of N are 157 kg ha^-1 for Kennebec and Shepody and 196 kg ha^-1 for Russet Burbank. All rows were machine-planted on 18 May and 1 June in 1999 and 2000, respectively. Recommended cultural practices were used (Bernard et al., 1993). Sencor was applied as a pre-emergence herbicide. Application of recommended insecticides and fungicides provided good control of all insect pests and potato late blight (causal agent: Phytophthora infestans).

Plots were harvested on 14 and 20 October in 1999 and 2000, respectively. Russet Burbank and Shepody tubers are grown for the processing french fry market and were graded according to the following size categories where: 1 is 51 mm diam., 2 is 51 mm diam. and <280 g, and 3 >280 g. (Size Categories 2 and 3 are the marketable grades.) Tubers from Kennebec were mechanically sized for the tablestock market and according to the Canadian Agricultural Standard Act for round type tubers, small is 38 to 57 mm, Canada no. 1 size is 57 to 89 mm, large size is 89 to 114 mm, and culls are <38 mm or >114 mm.

Data collected included total yield, number of tubers per size class, and yield per size class. Tubers were evaluated for potato tuber diseases, including potato common scab [causal agent: Streptomyces scabies (Thaxt.) Waksm. & Henrici], wilt (causal agent: Fusarium oxysporum Schl.), and potato black scurf (causal agent: Rhizoctonia solani Kühn); foliar diseases, including late blight and early blight (causal agent: Alternaria solani Sorauer); and the physiological disorder hollow heart. Diseases were rated according to indices developed by National Institute of Agricultural Botany (1985).

Interactions between years were nonsignificant, so data from the 2-yr study were pooled and analyzed using Genstat (Payne, 1993). Tuber count data were examined for normal distribution, and data transformation was found not to be necessary. Data were analyzed as split plots, with red clover cultivars as whole plots and potato cultivars as subplots. When a significant treatment effect was found and there was no interaction, the test of least significant difference (LSD, P = 0.05) was used to separate means.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Red clover cultivar had no significant effect on the potato cultivars Kennebec and Russet Burbank. There were no significant differences in the level of plant disease present in any of the treatment plots or in the physiological disorder hollow heart (data not shown). Shepody potato in the plots following AC Kingston red clover had the highest number of tubers in Class Sizes 1 and 2 and the highest numbers of tubers per plot and per plant (Table 1). However, differences were significant only for Class Size 1 and total tubers per plot and per plant. Total numbers of tubers per plot were significantly higher (P = 0.05) following cultivars Prosper and AC Kingston.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
Crop rotations designed to maximize beneficial soil microbial populations in the root zone have the potential to promote and moderate potato growth. Thus, we found that, of the red clover cultivars tested, AC Kingston was best in combination with cultivar Shepody under the climatic conditions and production practices prevailing in Prince Edward Island. Shepody is one of the main potato cultivars used for the processing market (french fries) in the early part of the season (September through January). One of the main disadvantages of Shepody compared with other varieties is the low number of tubers produced per plant. Growers are paid principally for potatoes in the Size 2 and 3 categories, and are given an extra pay bonus for the percentage of tubers in the Size 3 category, but receive little or nothing for Size 1 tubers. Clearly, it would benefit growers to use systems of production that could maximize the yields of potato in profitable size categories.

From previous studies, Arsenault et al. (2001) showed that number of tubers per plant, N application, and the in-row seed piece spacing of a cultivar will, for the greater part, determine tuber size and yield (Arsenault et al., 2001). Russet Burbank can produce 10 to 15 tubers per plant and is usually planted at seed spacing of 38 cm to maximize the yield of processing size tubers. In contrast, Shepody normally has five to eight tubers per plant and is therefore planted at a closer in-row seed piece spacing (25 cm) to maximize the yield of optimum processing size categories of tuber. Potato in the Size 1 class has the potential to become Size 2 and 3 tubers under suitable conditions. From our knowledge of this system, planting Shepody following AC Kingston (or Atlas) at a wider spacing should increase the number and yield of Size 2 and 3 tubers. An additional and general benefit of the red clover rotation appeared to be a 38 kg ha^-1 reduction in the recommended rate of applied N, without any apparent yield penalty. Thus, we found that yields, in all cases, were consistent with those achieved in neighboring fields and comparable to those for potato grown under conventional rates of N during the same 2-yr period.

Consequently, it appears that crop rotation selection criteria that also consider the beneficial effects of rhizobacterial communities in cultivar-complementary rotations can be used when considering the long-term consequences of those crop sequences. We encourage breeding programs to examine the ability of any given line to manipulate its root zone microflora with respect to its own needs and to those of subsequent crops, with a view to engineering communities of beneficial rhizobacteria for complementary crops in rotation combinations.

Sturz (1995) reported that potato tuberization was influenced by release of bacteria following the breakdown of the mother tuber. The present study provides further evidence that the preceding red clover variety can also have an effect on the yield performance of the following potato cultivar, and this we attribute to rhizobacteria shared between red clover and potato cultivars (Sturz et al., 1998). Because the complexities of plant–soil–microbial interactions are great, it appears unlikely that a complete understanding of all the relationships involved will ever be achieved, even under production monoculture. Even so, those beneficial biological interactions that stimulate crop yields and improve plant health can be evaluated relatively simply, and general management strategies can be devised for any given set of crop combinations and growing environments.

	ACKNOWLEDGMENTS

 
The authors wish to thank Brian Matheson, Bill MacMicken, and Ambrose Malone for their technical help during this study.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Sturz, A. V. Articles by Christie, B. R. Search for Related Content PubMed Articles by Sturz, A. V. Articles by Christie, B. R. Agricola Articles by Sturz, A. V. Articles by Christie, B. R. Related Collections Allelopathy Crop Ecology Crop Growth and Development Crop Rotation Systems Clover Potato