There have been reports of cover crops increasing the yield of the following crops (Clark, 2007; Dabney et al., 2010; Delgado et al., 2007). However, there is a need for additional research on the potential benefits that cover crops may have on the yields of the following potato crop.
There have been studies on the effect of nitrogen (N) fertilizer inputs and N cycling from cover crops on yields. For example, Neeteson (1988) reported higher potato yields at low N fertilizer rates following leguminous crops that have a lower carbon (C):N ratio and a higher N cycling (N mineralization) potential, such as red clover (Trifolium pratense) and alfalfa (Medicago sativa). Conversely, Neeteson (1988) reported lower yields were observed for potato following oat (Avena sativa), which is a cover crop with higher C:N ratio and lower potential to mineralize N. Neeteson (1988) found that at optimal N fertilizer rates, potato tuber yields were slightly lower following legumes.
Results from studies conducted by Sincik et al. (2008) indicated that potato following legume cover crops produced ≈36% to 38% higher tuber yields compared with potato following winter wheat (Triticum aestivum) when zero N was applied. In other legume studies, Odland and Sheehan (1957) and Emmond and Ledingham (1972) reported higher potato yields following legumes than non-legumes crops, but Murphy et al. (1967) found no yield benefits following legumes. The authors of the present study suggest that these effects of legumes or non-legume cover crops on tuber yield responses could have been in part due to potential responses of potato cultivars to the increased availability of N. For example, Essah and Delgado (2009) found that excessive application of N fertilizer reduced potato tuber yields and tuber quality and that this response was dependent on the type of potato cultivar. In other words, in cases where the amount of N is increased to higher levels than needed, a negative effect could then be observed (Essah and Delgado, 2009). Further, when N is applied in better synchronization with the N demands of a given potato cultivar (and the N that is cycled is accounted for when applying N), tuber yields could be increased (Essah and Delgado, 2009). Since cover crops have the potential to affect the N balance of the following crop (Delgado, 1998; Delgado et al., 2001, 2010), this could be one of the factors that could potentially contribute to effects on tuber yields and quality (Delgado et al., 2007; Essah and Delgado, 2009).
Cover crops can be good soil scavengers of N and they can cycle significant amounts of the recovered N to the following crop (Collins et al., 2007; Delgado et al., 2004, 2010; Seo et al., 2006; Varco et al., 1989). Vyn et al. (2000) conducted studies in Canada and found that cover crops, such as annual ryegrass, oat, oilseed radish (Raphanus sativus), or even red clover, could serve as scavenger crops that can recover residual soil nitrate and potentially cycle it to the following crop.
Delgado et al. (2007) reported other benefits from summer cover crops grown with limited irrigation and observed a 12% to 30% increase in total yield and marketable tubers when potato followed sorghum-sudangrass, with a greater increase in large tubers. Cover crops that have been found to provide soil disease suppression of verticillium wilt (Verticillium dahliae) of potato include barley, corn (Zea mays), rape (Brassica rapa), oat, ryegrass, sudangrass (Sorghum sudanense), and wheat, with sudangrass showing the greatest potato yield response for marketable-size tubers (Davis et al., 1994). The studies by Davis et al. (1994) clearly show that there are several other parameters that can impact tuber yield and quality, such as disease suppression, in addition to the effects of nutrient availability and cycling of N from the cover crop.
In most studies conducted on cover crops and potato performance, the effect of the cover crop on tuber size distribution and on tuber quality is not well documented. There remains a need for studies on the effect of different cover crops on potato total tuber yield and also on potato tuber size distribution and tuber quality. The goal of the present study was to analyze the effects of several cover crops on potato tuber yield, potato tuber size distribution, and tuber quality, as measured by tuber external and internal defects.
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