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type of . In other words, Cover Can Improve Potato in cases where the amount of N is in- Yield and Quality creased to higher levels than needed, a negative effect could then be ob- served (Essah and Delgado, 2009). Samuel Y.C. Essah1,5, Jorge A. Delgado2, Merlin Dillon3, Further, when N is applied in better and Richard Sparks4 synchronization with the N demands of a given potato cultivar (and the N that is cycled is accounted for when ADDITIONAL INDEX WORDS. tuber size distribution, tuber external defects applying N), tuber yields could be in- creased (Essah and Delgado, 2009). UMMARY tuberosum S . There is the need to develop potato ( ) cropping Since cover crops have the potential systems with higher yields and quality. Field studies were conducted with cover crops grown under limited irrigation (<8 inches) to assess the effects of certain types to affect the N balance of the follow- of cover crops on potato tuber yield and quality. On a commercial farm operation ing crop (Delgado, 1998; Delgado before the 2006 and 2007 potato season, mustard (Brassica sp.), canola (Brassica et al., 2001, 2010), this could be one napus), and two of -sudangrass ( · S. sudanense) of the factors that could potentially were planted. A wet fallow ground treatment where no cover crop was planted was contribute to effects on tuber yields used as a control. Before the 2008 season, (Hordeum vulgare), barley plus and quality (Delgado et al., 2007; applied compost, sunflower (Helianthus annus), pea (Pisum sativum), and annual Essah and Delgado, 2009). ryegrass (Lolium multiflorum) cover crops were added. The results of these 2006– Cover crops can be good soil scav- 08 studies showed that cover crops have the potential to increase potato tuber yield engers of N and they can cycle signifi- and quality, as measured by tuber size (larger ) and appearance (e.g., tubers cant amounts of the recovered N with reduced defects such as cracks, knobs, and misshapes). In 2 of the 3 years, most of the cover crops, especially sorghum-sudangrass, increased yields and tuber to the following crop (Collins et al., quality. Positive results from sorghum-sudangrass suggest there is potential to 2007; Delgado et al., 2004, 2010; harvest hay from cover crops and still obtain tuber benefits. Seo et al., 2006; Varco et al., 1989). Vyn et al. (2000) conducted studies in and found that cover crops, here have been reports of cover potato tuber yields were slightly lower such as annual ryegrass, , oilseed crops increasing the yield of the following . radish (Raphanus sativus), or even red Tfollowing crops (Clark, 2007; Results from studies conducted clover, could serve as scavenger crops Dabney et al., 2010; Delgado et al., by Sincik et al. (2008) indicated that that can recover residual soil nitrate 2007). However, there is a need for potato following cover crops and potentially cycle it to the follow- additional research on the potential produced 36% to 38% higher tuber ing crop. benefits that cover crops may have on yields compared with potato follow- Delgado et al. (2007) reported the yields of the following potato crop. ing winter (Triticum aestivum) other benefits from summer cover crops There have been studies on the when zero N was applied. In other grown with limited irrigation and ob- effect of nitrogen (N) fertilizer inputs legume studies, Odland and Sheehan served a 12% to 30% increase in total and N cycling from cover crops on (1957) and Emmond and Ledingham yield and marketable tubers when po- yields. For example, Neeteson (1988) (1972) reported higher potato yields tato followed sorghum-sudangrass, reported higher potato yields at low following legumes than non-legumes with a greater increase in large tubers. N fertilizer rates following legumi- crops, but Murphy et al. (1967) found Cover crops that have been found to nous crops that have a lower carbon no yield benefits following legumes. provide soil disease suppression of ver- (C):N ratio and a higher N cycling The authors of the present study sug- ticillium wilt ( dahliae)of (N mineralization) potential, such as gest that these effects of legumes or potato include barley, corn (Zea mays), red clover (Trifolium pratense) and non-legume cover crops on tuber yield rape (Brassica rapa), oat, ryegrass, alfalfa (Medicago sativa). Conversely, responses could have been in part due sudangrass (Sorghum sudanense), and Neeteson (1988) reported lower yields to potential responses of potato culti- wheat, with sudangrass showing the were observed for potato following oat vars to the increased availability of N. greatest potato yield response for (Avena sativa), which is a cover crop For example, Essah and Delgado marketable-size tubers (Davis et al., with higher C:N ratio and lower poten- (2009) found that excessive applica- 1994). The studies by Davis et al. tial to mineralize N. Neeteson (1988) tion of N fertilizer reduced potato (1994) clearly show that there are found that at optimal N fertilizer rates, tuber yields and tuber quality and that several other parameters that can im- this response was dependent on the pact tuber yield and quality, such as

1Department of Horticulture and Landscape Archi- tecture, Colorado State University, San Luis Valley Research Center, Center, CO 81125 Units 2USDA, Agricultural Research Service, Fort Collins, To convert U.S. to SI, To convert SI to U.S., CO 80526 multiply by U.S. unit SI unit multiply by 3 Colorado State University (former), Monte Vista, 0.3048 ft m 3.2808 CO 81144 2.54 inch(es) cm 0.3937 4USDA NRCS, Center, CO 81125 25.4 inch(es) mm 0.0394 5Corresponding author. E-mail: [email protected]. 28.3495 oz g 0.0353 edu. 2.2417 ton/acre MgÁha–1 0.4461

• April 2012 22(2) 185 RESEARCH REPORTS disease suppression, in addition to the previous years of 2006 and 2007. Ap- means were compared using Fisher’s effects of availability and cy- plied compost was at the rate of protected least significant differ- cling of N from the cover crop. 4tons/acre. ence (LSD)testatthe0.05levelof In most studies conducted on Potato plots were harvested for probability. cover crops and potato performance, the 2006, 2007, and 2008 treatments. the effect of the cover crop on tuber Each randomized complete-block was Results and discussion size distribution and on tuber quality set up so that each plot had four rows TUBER YIELD AND TUBER SIZE is not well documented. There re- with between row spacing of 33 inches, DISTRIBUTION. For 2006, ‘Rio Grande mains a need for studies on the effect with tubers planted at in-row Russet’ tubers responded to cover crop of different cover crops on potato total spacingof11to12inches.Thepotato treatments compared with a wet fal- tuber yield and also on potato tuber crop was planted between 10 and 15 low system (P < 0.05, Table 1). In size distribution and tuber quality. The May and harvested between 15 and 20 2006, yield increased and tuber size goal of the present study was to ana- Sept. each year by harvesting the two increased when potato followed ‘Sor- lyze the effects of several cover crops middle rows of each plot using an ex- dan 79’ sorghum-sudangrass with all on potato tuber yield, potato tuber perimental plot potato digger at the of the aboveground incorpo- size distribution, and tuber quality, as farmersfield,theweekbeforecom- rated, or even when the aboveground measured by tuber external and inter- mercial harvesting operations at the ‘Sordan 79’ biomass was harvested nal defects. field site started. For each plot, total for hay. Total tuber yields and yields tuber yield was measured and tubers of marketable-size (>4oz)tuberswere Materials and methods were sorted into various size distribu- increased with both ‘Sordan 79’ treat- The present study was conducted tion groups based on tuber weight ments. Larger tubers (>10 oz and 10– at the San Luis Valley in south-central (<4 oz, >4 oz, >10 oz, 4–10 oz, and 16 oz) were produced in both ‘Sordan Colorado (lat. 3740#N, long. 1069#W, 10–16 oz). Size distribution groups 79’ treatments compared with the wet 2310 m altitude). Field studies were are very important because different fallow treatment. conducted under commercial grower markets demand different size groups. In 2006, when the size of the tubers operations from 2006 to 2008, using Also, in the fresh market industry larger following both sorghum-sudangrass the traditional best management prac- tubers attract premium . Addi- cultivars was compared with the size of tices recommended by Colorado State tionally, tuber external (growth cracks, the tubers following canola and mus- University (S.Y.C Essah, unpublished knobs, and misshapes) and internal tard, it was found that both sorghum- data). Cover crops and potato were (hollow heart and brown center) de- sudangrass cultivars contributed to grown under center-pivot irrigation fects were evaluated. Tuber internal higher total and marketable-size (>4 over a coarse-textured sandy soil with defects were evaluated by cutting into oz) tuber yields, as well as to the yield low soil organic matter (<1.5%). Each half all harvested tubers that were 8 oz of larger (>10 oz) tubers than the year, a randomizedcomplete-block de- or more in weight. canola and mustard cover crops. Al- sign with five replicated plots (35 ft Statistical analysis was conducted though canola, mustard, and wet fal- long by 12 ft wide) was established to using analysis of variance [ANOVA low total yield and marketable-size the cover crops. The cover crop (SAS version 9.2; SAS Institute, Cary, yields were not significantly different plots were established on a commercial NC)]. ANOVA was performed for among themselves, the canola cover field where the rest of the field was total tuber yield, tuber size distribu- crop contributed to larger tubers (>10 planted to sorghum-sudangrass, except tion groups, and tuber quality param- oz and 10–16 oz) than the wet fallow the randomized block area. Limited ir- eters. Differences among treatment and mustard. In summary, in 2006, rigation was applied each year to min- imize irrigation use cost. Three to five irrigation events were applied for a to- Table 1. Effects of preceding cover crop on tuber yield and tuber size distribution tal irrigation of 7 inches. of ‘Rio Grande Russet’ potato grown in 2006 at the San Luis Valley in south- central Colorado. Cover crops planted before the 2006 and 2007 ‘Rio Grande Russet’ Tuber yield (MgÁha–1)z potato planting included: 1) ‘Super <4 >4 >10 4–10 10–16 Sweet’ sorghum-sudangrass, 2) ‘Sordan Treatment Total oz oz oz oz oz 79’ sorghum-sudangrass, 3) ‘Sordan Wet fallowy 47.0 9.3 37.7 6.7 31.0 6.4 79’ with the tops removed for hay, 4) Sorghum-sudangrass 50.3 9.5 40.8 10.9 30.0 10.5 mustard, and 5) canola. A wet fallow Mustard 45.3 10.0 35.3 7.9 27.4 6.7 ground treatment was included as a ‘Sordan 79’ sorghum-sudangrass 51.3 8.3 43.1 15.5 27.6 14.3 control, where no cover crops were ‘Sordan 79’ sorghum-sudangrass 51.7 7.8 43.9 12.2 31.7 11.0 planted, but the same amount of ir- with hay removed rigation was applied as the treatments Canola 44.1 8.1 36.0 11.0 25.0 10.7 with cover crops. Additional cover crops LSDx 3.8 NS 4.0 2.7 2.4 2.6 that were added to the study to precede CV (%) 5.9 26.7 7.7 19.2 6.2 19.9 the 2008 ‘Russet Norkotah’ planting z<4 oz = small tubers that are not marketable in the fresh market, >4 oz = marketable tubers, >10 oz = large included: 1) barley, 2) barley plus ap- marketable size tubers, 4–10 oz = medium size marketable tubers, 10–16 oz = large marketable size tubers without plied compost, 3) sunflower, 4) pea, 5) the jumbos; 1 oz = 28.3495 g, 1 MgÁha–1 = 0.4461 ton/acre. yControl treatment (bare ground) with no cover crop planted. annual ryegrass, and the previous cover xLeast significant difference at P < 0.05 comparing means between cover crops and wet fallow (control); NS = no crops and fallow system used for the significant difference.

186 • April 2012 22(2) the sorghum-sudangrass cultivar con- Table 2. Effects of preceding cover crop on tuber yield and tuber size distribution tributed to higher yields and larger of ‘Rio Grande Russet’ potato grown in 2007 at the San Luis Valley in south- tubers and the canola contributed to central Colorado. larger tubers than potato following a Tuber yield (MgÁha–1)z wet fallow system. <4 >4 >10 4–10 10–16 In 2007, among treatments there Treatment Total oz oz oz oz oz were no significant differences (P < y 0.05) in total and marketable-size (>4 Wet fallow 48.6 13.6 35.0 6.2 28.8 6.2 oz) tuber yields, and there were no Sorghum-sudangrass 50.1 11.4 38.7 5.0 33.8 5.0 significant differences in terms of tu- Mustard 44.6 10.3 34.3 4.0 30.3 4.0 ber size (>10 oz, 4–10 oz, 10–16 oz) ‘Sordan 79’ sorghum-sudangrass 47.4 12.2 35.1 4.1 31.0 3.8 (Table 2). Although there were no ‘Sordan 79’ sorghum-sudangrass 48.0 11.7 36.3 5.9 30.5 5.5 significant differences in the produc- with hay removed Canola 48.9 12.9 36.0 3.8 32.2 3.8 tion of large tubers, there was a differ- x ence in the production of economic LSD NS 1.7 NS NS NS NS size tubers with wet fallow resulting in CV (%) 5.8 10.8 9.6 32.9 10.4 38.7 z<4 oz = small tubers that are not marketable in the fresh market, >4 oz = marketable tubers, >10 oz = large the highest production of small tubers marketable size tubers, 4–10 oz = medium size marketable tubers, 10–16 oz = large marketable size tubers without (<4 oz) when compared with tubers the jumbos; 1 oz = 28.3495 g, 1 MgÁha–1 = 0.4461 ton/acre. following ‘Super Sweet’ sorghum- yControl treatment (bare ground) with no cover crop planted. xLeast significant difference at P < 0.05 comparing means between cover crops and wet fallow (control); NS = no sudangrass, mustard, or ‘Sordan 79’ significant difference. sorghum-sudangrass with all above- ground biomass harvested for hay. In summary, in 2007, the wet fallow Table 3. Effects of preceding cover crop on tuber yield and tuber size distribution resulted in greater production of small of ‘Russet Norkotah’ potato grown in 2008 at the San Luis Valley in south- tubers; however, these small tubers are central Colorado. not marketable and have low commer- Tuber yield (MgÁha–1)z cial value (P < 0.05, Table 2). <4 >4 >10 4–10 10–16 In 2008, ‘Russet Norkotah’ tu- Treatment Total oz oz oz oz oz ber production and tuber size groups Wet fallow y 50.1 13.1 37 1.8 35.2 1.8 responded to cover crop treatments Barley 58.8 14.7 44.1 3.8 b 40.2 3.1 compared with a wet fallow system Barley and compost applied 46.5 8.4 38.1 4.9 33.2 4.5 (P < 0.05, Table 3). In this year, both Sunflower 52 10.7 41.3 6.2 35.1 6.2 sorghum-sudangrass cultivars had a ‘Sordan 79’ sorghum-sudangrass 57.9 17.3 40.6 2.1 38.5 2.1 positive impact on tuber production ‘Sordan 79’ sorghum-sudangrass 63 15.6 47.5 5.1 42.4 4.3 and tuber size. ‘Sordan 79’ increased with hay removed total tuber yield and quality compared Sorghum-sudangrass 48.6 11.1 37.5 4.5 33.1 4.1 with wet fallow. Total yield produc- Canola 503 11.8 38.5 4.2 34.3 4.2 tion was higher following the ‘Sordan Mustard 47 9.1 37.9 2.8 35.1 2.5 79’ with all aboveground biomass Pea 55.6 14.8 40.8 5.2 35.5 5.2 incorporated or harvested for hay treat- Ryegrass 57.2 11.8 45.4 6.3 39.1 6.3 ments than following a wet fallow sys- LSDx 6.0 2.2 5.8 1.5 5.7 1.2 tem. Marketable-size tuber yields (>4 CV (%) 8.8 13.0 11.1 27.9 12.2 22.9 oz) and yields of larger tubers (>10 oz z<4 oz = small tubers that are not marketable in the fresh market, >4 oz = marketable tubers, >10 oz = large and 10–16 oz) following ‘Sordan 79’ marketable size tubers, 4–10 oz = medium size marketable tubers, 10–16 oz = large marketable size tubers without with all aboveground biomass har- the jumbos; 1 oz = 28.3495 g, 1 MgÁha–1 = 0.4461 ton/acre. vested for hay were higher than when yControl treatment (bare ground) with no cover crop planted. xLeast significant difference at P < 0.05 comparing means between cover crops and wet fallow (control). following wet fallow. Additionally, when production followed the ‘Super Sweet’, there was also an increase in tubers (>10 oz and 10–16 oz) com- however, barley and compost had re- the quantity of larger tubers (>10 oz pared with a wet fallow system. duced total and marketable tuber pro- and 10–16 oz) compared with when When potato followed a ryegrass ductionwhencomparedwithbarley following a wet fallow system. or sunflower cover crop, more large alone. Potato following a barley or - size tubers (>10 oz and 10–16 oz) Mustard did not improve the pro- grass cover crop had higher total and were produced compared with when duction of larger (>10 oz) tubers when marketable-size (>4 oz) tuber yields it followed a barley cover crop. Potato compared with wet fallow or barley. than when following wet fallow. The following ‘Sordan 79’ with all above- Mustard did not improve total tuber barley and ryegrass cover crops also ground biomass harvested for hay, yields or marketable yields, and total contributed to the production of lar- or the pea cover crop, had increased and marketable tuber yields with mus- ger tubers (>10 oz and 10–16 oz) com- large size tubers (10–16 oz) when tard were lower than with barley. paredwiththewetfallowsystem.Potato compared with potato following bar- TUBER EXTERNAL AND INTERNAL following a barley cover crop that re- ley. The barley and compost treatment DEFECTS. For 2006, ‘Rio Grande Rus- ceived compost, or canola, sunflower, had increases of large tubers (10–16 set’ responded to cover crop treat- or pea cover crops also produced larger oz)whencomparedwithbarleyalone; ments with improved tuber quality,

• April 2012 22(2) 187 RESEARCH REPORTS represented by a reduced percentage lower percentage of external defects losses in profit. It is important to note of tuber external defects (P < 0.05, than the barley. that the use of canola, mustard, and Table 4). In 2006, the treatment with In these studies, no hollow heart ‘Sordan 79’ reduced external defects the higher percentage of external defects or brown center (internal defects) were in the tubers that followed, compared was the wet fallow treatment; with over observed in any of the tubers harvested. with tubers that followed the use of 3% of the tubers produced, following SUMMARY. Field studies were con- barley. Across these three field studies, this treatment, having external defects. ducted under commercial farm opera- the mustard did not provide as great ‘SuperSweet’sorghum-sudangrass,mus- tions to assess the effects of different of an advantage over the wet fallow. tard, ‘Sordan 79’ sorghum-sudangrass cover crops on the yields and quality The results presented in this arti- with all aboveground biomass harvested of the potato tubers that followed, as cle are in agreement with the Delgado for hay, and canola all had reduced measured by tuber size and appearance et al. (2007) finding that sorghum- percentage of external defects such as (e.g., reduced percentage of cracks, sudangrass can contribute to higher cracks, knobs, and misshapes, when knobs, and misshapes). These studies yields and larger tubers. Additionally, compared with the wet fallow treat- were conducted from 2006 to 2008, the present study shows that there are ment. Most of the cover crops had and on average cover crops provided several other cover crops in addition reduced external defects by 50%, bring- a significant advantage over wet fal- to sorghum-sudangrass that can pro- ing the percentage down to 1.5% or low, contributing to increased yields, vide tuber production and quality lower. Mustard had nearly no exter- larger tubers, and better tuber qual- advantages. nal defects, with 0.3%. ity (tubers with less external defects) Looking at the tuber responses For 2007, the external defects (P < 0.05, Table 5). In two of the as far as production (yields), size, data were not presented since there three studies, the sorghum-sudangrass and quality (tuber defects), during were minimal external defects at the showed an advantage in increasing 2006, positive effects were achieved site (across all treatments <0.5%). Only tuber yields and quality, providing when potato followed either sorghum- ‘Super Sweet’ and ‘Sordan 79’ sor- the farmer with additional income sudangrass cultivar. Even when the ghum-sudangrass showed any external compared with a wet fallow system aboveground biomass for ‘Sordan 79’ defects, which were <0.5%. All other (P < 0.05, Table 5). Only for two of was removed for hay, there was still a treatments had zero external defects. the three studies did we report tuber positive response in potato tuber pro- For 2008, ‘Russet Norkotah’ also external defects, since in one study duction and quality. The results suggest responded to cover crop treatments the percentage of external defects for that both the belowground material compared with a wet fallow system. In all treatments was less than 0.5%. and the aboveground litter left behind this year, the treatment with the high- For the two studies with measurable after harvesting the cover crop for hay est rate of external defects was the wet external defects above 2% for some are playing an important role, poten- fallow treatment, with close to 2% de- treatments, the cover crops were ben- tially contributing to soil biological and fects (Table 4). On average, all of the eficial and reduced the percentage of biogeochemical factors that may be cover crops reduced the percentage of tuber external defects compared with providing the mechanism for the po- external defects by 50%, with only the wet fallow. For these two studies, tato physiological response. 1% or less of the tubers showing ex- cover crops reduced external defects Additionally, several cover crops ternal defects. ‘Sordan 79’ sorghum- on average by 50% over the wet fallow, such as the ryegrass and ‘Sordan 79’ sudangrass and mustard resulted in a helping to minimize the potential for with all the aboveground biomass har- vested for hay also showed the potential to produce the same marketable-size Table 4. Effects of preceding cover crop on tuber external defects of ‘Rio Grande yields with larger tubers and better Russet’ and ‘Russet Norkotah’ potato grown in 2006 and 2008, respectively, at tuber quality (tubers with less external the San Luis Valley, south-central Colorado. defects) than the barley cover crop. Tuber external defects (%)z Delgado et al. (2007) found a corre- Treatment 2006 2008 lation between tuber yields and the nutrient content of the preceding cover Wet fallowy 3.1 1.8 crop. Davis et al. (2010) found that the Barley — 0.9 preceding cover crops affected soil bi- Barley and compost applied — 0.9 ology, contributing to yield responses. Sunflower — 0.6 The underlying mechanisms that are ‘Sordan 79’ sorghum-sudangrass 2.3 0.2 causing these physiological responses ‘Sordan 79’ sorghum-sudangrass 1.7 0.8 by the potato crop are unknown and with hay removed are beyond the scope of this article. Sorghum-sudangrass 1.4 0.9 However, the responses of potato fol- Canola 1.1 0.7 lowing a grain cover crop, a leguminous Mustard 0.3 0.2 crop,orevenagraincovercropwith Pea — 1.0 compost, all of which are presented in Ryegrass — 0.9 this article, suggest that the mecha- LSDx 0.8 0.5 nisms are very complex. Additional re- CV (%) 43.6 52.2 search in this area will be needed to zIncludes growth cracks, knobs, and misshapes. yControl treatment (bare ground) with no cover crop planted. model some of these physiological re- xLeast significant difference at P < 0.05 comparing means between cover crops and wet fallow (control). sponses and to better understand the

188 • April 2012 22(2) Table 5. Summary of the general trend with respect to the effects of preceding cover crop, ‘Sordan 79’ sorghum-sudangrass with aboveground biomass removed for hay treatment, the barley and compost applied treatment, and the wet fallow (bare ground) on ‘Rio Grande Russet’ (2006 and 2007) and ‘Russet Norkotah’ (2008) potato grown at the San Luis Valley in south-central Colorado. Trendz Treatment 2006 2007 2008 2008 2008 Wet fallowy baseline baseline baseline YP: YQ: D[ =P: YQ: [D[ Barley — — [P: [Q: YD baseline [P: =Q: =D= Barley and compost applied — — =P: [Q: YD YP: [Q: =D baseline Sunflower — — =P: [Q: YD =P: [Q: =D =P: [Q: =D ‘Sordan 79’ sorghum-sudangrass =P: [Q: =D =P: =Q: =Dz [P: =Q: YD =P: YQ: YD [P: YQ: YD ‘Sordan 79’ sorghum-sudangrass [P: [Q: YD =P: =Q: =Dz [P: [Q: YD =P: [Q: =D [P: =Q: =D with hay removed Sorghum-sudangrass =P: [Q: YD =P: =Q: =Dz =P: [Q: YD YP: =Q: =D =P: =Q: =D Canola =P: [Q: YD =P: =Q: =Dz =P: [Q: YD YP: =Q: =D =P: =Q: =D Mustard =P: =Q: YD =P: =Q: =Dz =P: =Q: YD YP: =Q: YD =P: YQ: YD Pea — — =P: [Q: YD =P: [Q: =D [P: =Q: =D Ryegrass — — [P: [Q: YD =P: [Q: =D [P: [Q: =D zP = production; an arrow pointing upwards for production ([P) indicates total tuber and/or marketable tuber production was increased. Q = tuber quality as determined by size; an arrow pointing upwards for tuber quality ([Q) indicates that larger tubers were produced [>10 oz and/or 10–16 oz (1 oz = 28.3495 g)]. D = external defects; an arrow pointing downward for external defects (YD) indicates that the external defects were reduced. Dz = there were no external defects in the whole study that were measureable (<0.5% external defects in all treatments). No change from the baseline is indicated by =. Arrows reflect effects at P < 0.05. An arrow pointing downward for P or Q indicates a downward production and quality, respectively. An = sign means no change. Table shows the general trends of the effects of cover crop treatments, the ‘Sordan 79’ sorghum- sudangrass with aboveground biomass removed for hay treatment, the barley and compost applied treatment, and the wet fallow (control) treatment. yControl treatment (bare ground) with no cover crop planted. soil–plant interface in cover crop– higher yields and better-quality tubers. in nitrogen management for water qual- potato systems. There is the need for additional research ity. Soil and Water Conservation Soc., on the soil–plant–microbiological in- Ankeny, IA. Conclusion teractions. This is a complex system; Davis, J.R., O.C. Huisman, D.O. Everson, The purpose of the 2006–08 stud- for example, Manter et al. (2010) re- P. Nolte, L.H. Sorensen, and A.T. ies was to evaluate the effects of certain ported that soil microbes inside the Schneider. 2010. Ecological relationships types of cover crops on tuber yield, as were correlated with tuber yields. More of suppression of potato well as to obtain new, additional in- information is needed to understand by green manures. Amer. J. Potato Res. formation on the effects of cover crops how we can manage systems to con- 87:315–326. on tuber size distribution and exter- tinue to achieve greater production Davis, J.R., J.J. Pavek, D.L. Corsini, L.H. nal defects. The results suggest that and higher-quality tubers, and the Sorensen, A.T. Schneider, D.O. Everson, although there is not yet a clear under- potential economic benefits for farms D.T. Westermann, and O.C. Huisman. standing of the mechanism (possible that may result. It is clear from this 1994. Influence of continuous cropping mechanisms could include but are not study that the tested cover crops are of several potato clones on the epidemi- necessarily limited to , sup- generating a positive, or in some in- ology of verticillium wilt of potato. Phy- pression of diseases, biogeochemistry stances, a negative effect on potato topathology 84:207–214. pathways and availability of macro and tuber yields and quality, and addi- Delgado, J.A. 1998. Sequential NLEAP micro , and the physiological tional research is needed to under- simulations to examine effect of early and responses by the potato at the root, stand the underlying mechanisms of late planted winter cover crops on nitro- tuber and aboveground), cover crops these effects. gen dynamics. J. Soil Water Conserv. 53: can potentially improve potato tuber 241–244. yields and quality and minimize exter- Delgado, J.A., S.J. Del Grosso, and S.M. nal tuber defects. Additionally, positive Literature cited Ogle. 2010. 15N Isotopic crop residue results from the sorghum-sudangrass Clark, A. (ed.). 2007. Managing cover exchange studies suggest that IPCC crop suggest that there is even potential crops profitably. 3rd ed. Sustainable Ag- methodologies to assess N2O-N emis- to use cover crops for hay production riculture Network, Beltsville, MD. sions should be reevaluated. Nutr. Cycl. while still keeping the tuber quality Collins, H.P., J.A. Delgado, A.K. Alva, Agroecosyst. 86:383–390. benefits of these crops. and R.F. Follett. 2007. Use of nitrogen- Delgado, J.A., M.A. Dillon, R.T. Again, although the mechanism 15 isotopic techniques to estimate nitro- Sparks, and R.F. Follett. 2004. Tracing behind these effects is not yet certain, gen cycling from a mustard cover crop to thefateof15N in a small-grain potato we propose that cover crops may im- potatoes. Agron. J. 99:27–35. rotation to improve accountability of pact soil biology and biogeochemical Dabney, S.M., J.A. Delgado, J.J. Meisinger, N budgets. J. Soil Water Conserv. 59: processes that impact the soil–root– H.H. Schomberg, M.A. Liebig, T. Kaspar, 271–276. plant system. The unique responses J. Mitchell, and W. Reeves. 2010. Using Delgado, J.A., M.A. Dillon, R.T. Sparks, presented in this article raise the ques- cover crops and cropping systems for ni- and S.Y.C. Essah. 2007. A decade of tion of how the potato plant receives a trogen management, p. 231–281. In: J.A. advances in cover crops. J. Soil Water signal to physiologically respond with Delgado and R.F. Follett (eds.). Advances Conserv. 62:110A–117A.

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