Some Unique Benefits with Sudangrass for Improved U.S. #1 Yields and Size of Russet Burbank Potato

American Journal of Potato Research, Nov/Dec 2004 by Davis, J R, Huisman, O C, Westermann, D T, Everson, D O, Et al

ABSTRACT

Three studies provided additional knowledge of beneficial effects of sudangrass for yield and quality increases of the Russet Burbank potato. Two of these studies showed significant increases of both U.S. #1 and smooth tubers >280 g following green manures of Sudangrass. These sudangrass (HS-33) effects did not differ from a sorghum-sudan hybrid (Trudan-8). When a Sudangrass green manure was compared with a fallow treatment, results of the first study showed mean yield increases of 36% for U.S. #1 tubers >280 g and yields of a second study by 34% for U.S. #1 tubers. This same sudangrass treatment outperformed green manures of either Austrian winter pea, barley, or sweet corn by increased U.S. #1 yields that ranged from 27% to 61%. By several lines of evidence, these benefits were found to extend beyond the effect of Verticillium suppression. Soil N was significantly increased following green manures of sudangrass, and these increases were in turn negatively correlated with wilt incidence and positively correlated with yields of both U.S. #1 tubers and tubers >280 g. Additional benefits also included significant increases of tuber grade percentages for marketable tubers and of smooth tubers >280 g. Benefits from sudangrass green manures beyond the effects of Verticillium suppression became further evident following a greenhouse study that involved field soil and sudangrass that had been grown in the same field. This study corroborated both field experiments by showing increased yields with green manures of sudangrass that approximated 5.5 t ha^sup -1^ dry wt. As with the field studies, these yield benefits also extended beyond the effects of Verticillium suppression and were closely associated with significant increases of Fusarium equiseti, F. oxysporum, and F. solani. Throughout all studies, sudangrass green manures significantly increased microbial activities with increased populations of Fusarium spp. and increased concentrations in soil of mineralizable N, organic P, K, Mn, along with the percent soil organic matter - all factors that could have contributed to significant increases of yield and quality.

Accepted for publication 7 June 2004.

ADDITIONAL KEY WORDS: Fusarium spp., green manures, Verticulium dahliae

RESUMEN

Se obtuvo informaci�n adicional sobre los efectos ben�ficos del sorgo para el incremento de rendimientos y calidad de papa Russet Burbank por medio de tres estudios. Dos de ellos mostraron un significativo incremento de U.S. #1 y tub�rcules uniformes >280g despu�s de haber recibido sorgo como abono verde. Los efectos del sorgo (HS-33) no mostraron diferencias con el sorgo h�brido (Tridan-8). Cuando se compar� el abono verde de sorgo con un tratamiento de barbecho, los resultados del primer estudio mostraron un promedio de incremento del rendimiento de 36% para tub�rculos U.S. #1 >280g y los del segundo estudio 34% para tub�rculos U.S. #1. El mismo tratamiento de sorgo, super� a los abonos verdes de alverjilla, cebada y ma�z dulce con rendimientos de U.S. #1 que variaron entre 27 y 61%. Junto con estas evidencias, los beneficios logrados fueron adem�s un efecto de supresion de Verticillium. El N del suelo se increment� significativamente despu�s de un abonamiento verde con sorgo y este incremento estuvo negativamente correlacionado con la incidencia de marchitez y positivamente con el rendimiento tanto de U.S. #1 como de tub�rculos >280g. Los beneficios adicionales tambi�n incluyen un incremento significativo del porcentaje de tub�rculos de grado comerciable y de tub�rculos uniformes >280g. Adem�s de los efectos de supresi�n de Verticillium, los efectos del abono verde con sorgo se hicieron evidentes despu�s de un estudio de invernadero que incluy� el uso de tierra de chacra y de sorgo que hab�a crecido en el mismo suelo. Este estudio corrobor� ambos experimentos de campo, mostrando un incremento de rendimiento de aproximadamente 5.5 t ha^sup -1^ de peso seco con el uso de sorgo como abono verde. Como en el caso de los estudios de campo, estos beneficios en el rendimiento tambi�n se extendieron m�s all� de los efectos de supresi�n de Verticillium y estuvieron estrechamente asociados con un incremento significativo de Fusarium equiseti, F. oxysporum y F. solani. A lo largo de todos los estudios, el uso de sorgo como abono verde increment� significativamente las actividades microbianas, con un aumento en la poblaci�n de Fusarium spp. e incremento de las concentraciones de N mineralizable, P,K y Mn org�nicos, junto con el porcentaje de materia org�nica en el suelo, factures todos que podr�an contribuir a un aumento de rendimiento y calidad.

INTRODUCTION

Among cropping practices, green manures can be highly effective for both the control of Verticillium wilt caused by Verticillium dahliae, and the improvement of yield and quality of potato (Davis et al. 1996; Huisinan et al. 1995). Green manure crops that have provided disease suppression include barley, com, rape, oats, rye, sudangrass, and wheat (Davis et al. 1996, 1999a, 1999b), but of these crops, sudangrass has to date provided the greatest yield response of U.S. #1 tubers and tubers >280 g with potato. Although the benefits of sudangrass on Verticillium wilt suppression cannot be directly explained by a reduction in soil populations of V. dahliae, these benefits can be explained by a reduction in number of root infections by V. dahliae (Davis et al. 1996).

Benefits from sudangrass, however, may extend beyond disease suppression (Davis et al. 1996). When a green manure crop of either oats or sudangrass was grown and incorporated for 2 years prior to a potato crop, the incidence of Verticillium wilt did not differ between these two green manures. Yet, tuber yields following sudangrass were significantly higher when compared to oats. This occurred even though the amount of green residue incorporated with the oats was greater than with sudangrass. A similar relationship between corn and Sudangrass also occurred. Even though wilt incidence and V. dahliae colonization did not differ between green manure treatments of corn and sudangrass, there was still a significant increase of tuber size of smooth tubers >280 g by 22% with sudangrass. The purpose of this study was to further investigate the effect of sudangrass on yield and quality of potato and its relationship to V. dahliae.

MATERIALS AND METHODS

Field studies were conducted at the University of Idaho Research and Extension Center, Aberdeen, ID, on a Declo loam soil with a pH of 8.0 to 8.2. Prior to 1992, the cropping histories of both fields included potatoes and small grains for >30 years.

Biomass Field Study with Sudangrass (Roots vs Foliage)-Experiment 1

Green manure treatments were arranged and grown for two consecutive years (1992 and 1993) in a 4 x 4 Latin square design on plots that were 5.5 x 15.2 m in size. Main plot treatments were split with a split-plot factorial design consisting of two sudangrass (Sorghum vulgare Pers. var. sudanense [Piper] Hitche.) varieties: HS-33 (CalWest Seeds, Woodland, CA) and Trudan-8 (Northrup King, Minneapolis, MN). Main plot treatments were (1) a weed-free fallow; (2) foliage of sudangrass that was removed and roots incorporated; (3) a fallow to which sudangrass cuttings were added; and (4) foliage and roots incorporated. Green manures were planted during last week of May each year and were incorporated by plow or rotovator in mid-August.

In both years, prior to incorporation of green manures, samples were collected from 1 m^sup 2^ of the buffer regions of each plot to provide an estimate of foliage residue to be incorporated into soil. These foliage samples were oven-dried at approximately 49 C for 2 wk before making weight determinations. The mean dry weights of sudangrass ha^sup -1^ for HS-33 and Trudan-8 were 11 and 12 tons, respectively, in 1992 and 5 tons ha^sup -1^ in 1993 for both HS-33 and Trudan-8. Weed control in plots was provided with applications of 2,4-D (water soluble amine) at 0.56 kg ha^sup -1^ in mid-June. Broadcast fertilizer applications of ammonium nitrate, phosphate, and triple superphosphate were based on soil assays taken prior to planting of both green manures and potatoes in the spring of each year (University of Idaho Soils Lab, Moscow, ID).

Certified, uncut seed (single drop) of cv Russet Burbank and cut seed (59 � 6 g) of cv Russet Norkotah were planted with an assist-feed planter in 3-row plots in 10.7-m row lengths during the first week of May 1994. Row width was 0.9 m and seed was spaced 30 cm apart in rows.

No systemic insecticides were applied, and all irrigations were applied with solid-set sprinklers. In general, cultural practices were as recommended by the University of Idaho for potato production (Anonymous 1986; Bishop et al. 1982; Kleinkopf et al. 1981; Ohms 1962; Westermann et al. 1994). Foliar sprays of either mancozeb at 1.8 kg ha^sup -1^ or chlorothalonil at 1.25 kg ha^sup -1^ were applied at weekly intervals between mid-July and 1 September to protect, against foliar diseases (early blight and black dot) that can reduce yield (Anonymous 1986; Mohan et al. 1992).