Interseeding cover crops into maize: Characterization of species performance under Mediterranean conditions

Highlights

• The crop diversification technique of cover crop interseeding was tested in a Mediterranean region.

• Nine species were interseeded into irrigated maize and compared to autumn cover crops.

• Ryegrass, common vetch, yellow sweetclover and barrel medic were the most suitable species.

• Maize grain yield and quality were not affected by interseeded crops.

• Interseeded crops lengthened cover crop benefits compared to autumn cover crops.

Abstract

Cover crop (CC) benefits and adoption in crop rotations may be limited by the short planting window after the cash crop. Interseeding or relay intercropping of CC is a technique that could overcome short planting windows constraints and allow CC establishment and growth. However, in Mediterranean regions this technique has been poorly implemented.

Field experiments were established in Central Spain during two consecutive growing seasons to assess the performance of different species as interseeded crops into irrigated maize (Zea mays L.). The treatments included annual ryegrass (Lolium multiflorum L.) and eight legumes: burr medic (Medicago polymorpha L.), barrel medic (Medicago truncatula L.), yellow sweetclover (Melilotus officinalis L.), berseem clover (Trifolium alexandrinum L.), balansa clover (Trifolium michelanium L.), red clover (Trifolium pratense L.), Persian clover (Trifolium resupinatum L.), and common vetch (Vicia sativa L.). A bare soil was included as control treatment. After the maize harvest, the four species with the best performance were planted as autumn cover crops in adjacent plots. The ground cover was studied throughout the experimental period, and biomass and N content for each species were determined in the autumn and in the following spring prior to the cover crop termination. The soil inorganic N content was determined in spring.

Barrel medic, yellow sweetclover, common vetch and annual ryegrass were the species with the best performance in terms of soil coverage during the summer. Red clover and Persian clover had good establishment in one out of two years. None of the interseeded species impaired maize grain yield or quality. Interseeded species achieved better soil coverage and increased the biomass accrued at autumn compared to cover crops sown in October. Therefore, interseeded species ensured longer ground coverage, increasing the potential for soil quality improvement or weed suppression. Moreover, the higher biomass achieved by interseeded species ensured the survival of yellow sweetclover, which was winter killed when planted in the autumn. Interseeded cover crops enhanced the potential of N leaching reduction compared to autumn cover crops.

This experiment confirms the suitability of different species interseeded in summer into irrigated maize in Mediterranean regions, and highlights the extra benefits of this practice in annual rotations.

Introduction

The use of cover crops (CCs) is a recognized practice that increases diversity and offers environmental benefits such as soil and water quality improvement, nutrient recycling and weed suppression in the agroecosystem (Schipanski et al., 2014; Gabriel et al., 2012). In annual rotations, CCs are mostly planted in autumn, replacing bare fallows, and terminated in spring (García-González et al., 2018), but the limited time window for planting was pointed out as one major reason for low CC adoption (CTIC (Conservation Technology Information Center), 2017; Roesch-McNally et al., 2018). In general, early planting (August–September) has been recommended to achieve greater biomass, N uptake and soil coverage during the growing period (Baraibar et al., 2018; Lawson et al., 2015; Teasdale et al., 2004). Due to the greater vegetative development, the planting date may be responsible for CC survival itself, since late planting can increase the winter kill risk, especially in legumes (Brandsæter et al., 2008; Teasdale et al., 2004) and therefore jeopardize the diversity in CC mixtures (Murrell et al., 2017). In addition, early planting dates may enhance weed suppression (Lawson et al., 2015) or ensure the CC termination efficacy in spring (Mirsky et al., 2009). Nevertheless, an early planting date choice is not always possible for the farmer. On the one hand, it depends on the previous cash crop, such as grain maize, that in some cases is harvested late. On the other hand, inclement weather may be responsible for the planting delay. Under semi-arid conditions, it is common to match the planting date with an autumnal rain, but this rain event may be delayed (Gabriel and Quemada, 2011).To overcome this problem, CCs could be established earlier in the rotation with relay intercropping (Bybee-Finley and Ryan, 2018; Hively and Cox, 2001), i.e., CC planting within the rows of the cash crop in an early vegetative stage. The relay intercropping or interseeding (IS) has been evaluated mainly in temperate climate regions. In most of these studies, IS species performance (Caswell et al., 2019; Curran et al., 2018) and the impact on the cash crop yield (Abdin et al., 1998; Noland et al., 2018) were assessed. A longer growing period can extend CC ecosystem services, and in years with high biomass production open the opportunity to harvest the CC or to terminate the CC in autumn for pasture (Gardner and Faulkner, 1991).

In Mediterranean systems, we could not find any study focus on IS of CC even if a short planting window was identified as a limitation for CC growth in years with unfavorable conditions for establishment (Gabriel and Quemada, 2011; García-Gonzalez et al., 2018; Salmerón et al., 2011). The strategies studied to increase temporal diversity in annual rotations have mainly focused on simultaneous cereal/legume intercrops (Hauggaard-Nielsen et al., 2009; Mariotti et al., 2015; Tosti et al., 2016), and the studies of IS crops have focused on winter cereals as main crops (Amossé et al., 2014; Vrignon-Brenas et al., 2016).

This study hypothesized that interseeded cover crops in irrigated maize vs. cover crops planted in autumn extend the cover crop window, lengthening their benefits in time, and offering new possibilities for annual rotation design. Our primary objective was to identify species with good performance as interseeded cover crops in irrigated maize under semiarid Mediterranean conditions. Moreover, interseeded crop performance was compared with autumn cover crops planted in October, in terms of ground coverage, biomass accumulation and soil inorganic N content.