**1. Introduction**

Winter malting barley (*Hordeum vulgare* L.) is an emerging crop in the Northeastern United States [1,2]. Although it has the potential to be a profitable crop in the region, achieving the high-quality grains needed for malting purposes is challenging because of the Northeast's humid environment and seasonal temperature extremes [3]. However, if the barley meets the malting quality standards, there is a price premium compared with feed grain [4] and the potential for additional local markets in the regional malting and brewing industry [5,6].

A successful malting barley crop must grow well, produce good yields of high-quality grain, and be harvested and stored correctly to maintain quality [7]. To be acceptable for malting, the barley grains should be large, low in protein, free of or very low in carcinogenic deoxynivalenol (DON) toxin [8], and sprout well during the malting process [9]. Farmers can successfully grow malting barley by combining three methods: (1) choosing a site-appropriate variety that will overwinter, resist locally common diseases, and remain upright after heading [10,11]; (2) correctly timing their harvest to avoid partial sprouting in the field and using forced air dryers if weather does not permit dry-down in the field [2,12]; and (3) using growing practices that have been shown to promote good malting quality [1,13].

Grain size is quantified by three metrics: test weight, percent plump, and percent thin. High test weight and high percent plump indicate that the kernels are large and

**Citation:** Siller, A.; Darby, H.; Smychkovich, A.; Hashemi, M. Winter Malting Barley Growth, Yield, and Quality following Leguminous Cover Crops in the Northeast United States. *Nitrogen* **2021**, *2*, 415–427. https://doi.org/10.3390/ nitrogen2040028

Academic Editor: Jacynthe Dessureault-Rompré

Received: 1 September 2021 Accepted: 5 October 2021 Published: 8 October 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

relatively uniform, while high percent thin means that the kernels are small with little energy for the malting process [7]. For the grains to sprout well during malting, they should have greater than 95% germinative energy and they must have a falling number greater than 250 s, indicating that they have not pre-sprouted in the field or during storage. Deoxynivalenol (DON) content must be below 0.5 mg kg−<sup>1</sup> while protein should be below 125 g kg−<sup>1</sup> [10,12]. While regional weather variability may prevent farmers from achieving malt-quality harvests in every year [2], the growing body of research into winter malting barley production can minimize this production risk for growers.

Previous research has produced varietal recommendations for malting barley growing in the Northeast [10,11] as well as recommendations for planting dates and fertilization rates [13,14]. However, winter malting barley is still a relatively new and minor crop in the Northeast [15] and most scientific reports are related to the drier areas of western North America.

In addition to selecting appropriate varieties and awareness of agronomic recommendations, it is essential that farmers understand how malting barley interacts with other crops in their rotations [16] and how other growing practices could influence crop rotation decisions. Since nitrogen can affect many aspects of barley malting quality, nitrogen cycling is of particular interest when considering how to integrate malting barley into a larger crop rotation. High levels of nitrogen fertilization can increase malting barley yields and grain size [17,18] but can also lead to excessive protein content [13,17–20], lower nitrogen use efficiency [13,17,19,21], and lower falling number [13]. While leguminous crops can contribute substantial amounts of nitrogen to subsequent crops, it is unknown whether nitrogen from legumes would have the same effects on winter malting barley as soluble nitrogen sources.

Since barley has the potential for producing a large number of tillers in the spring, the final yield does not respond linearly to increased planting density [22,23]. However, higher seeding rates may counteract the effect of excess nitrogen since higher seeding rates can reduce protein concentration and grain size [20,24]. The impact of crop rotation patterns may also be more noticeable in the fall when the plants are small [23] and different seeding rates may be differentially productive following a nitrogen-producing legume than a summer fallow.

Sunn hemp (*Crotalaria juncea* L.) and crimson clover (*Trifolium incarnatum* L.) are grown in the Northeast as summer forages or cover crops and can fit well into short growing periods before winter barley planting in the fall [25,26]. Farther north in eastern North America, Darby et al. [23] reported that barley yield was lower following sunn hemp but its malting quality was not affected, while crimson clover did not impact barley growth relative to summer fallow. In western North America, winter malting barley has also performed well following peas (*Pisum sativum* L.) and canola (*Brassica napus* L.) [16,17] but these crops are not commonly grown in the Northeast, and local rotation recommendations are needed. Whether grown as forages or cover crops, sunn hemp and crimson clover can have many impacts on agricultural productivity and ecosystem services. They can protect the soil from erosion [27], contribute organic matter to the soil [26], reduce insect pest damage [28,29], provide income if harvested as a forage [26,27], and add plant-available nitrogen to the soil [27,30].

In many rotations, the nitrogen contribution from sunn hemp or crimson clover would be beneficial to the following crop, but this may not be the case for winter malting barley if nitrogen from the preceding crop leads to excessive grain protein or otherwise reduces malting quality. Alternatively, if nitrogen from leguminous cover crops does not negatively affect malting barley, this would suggest that farmers can plant winter malting barley with minimal concern about excess nitrogen contributions from preceding crops.

The current experiment examines how integrating legumes into winter malting barley cultivation can affect grain yield and quality, and whether the barley seeding rate changes these effects. This knowledge will complement previous varietal assessment and agronomic

management recommendations to help farmers improve their profitability and integrate winter malting barley into their overall farm systems.

#### **2. Materials and Methods**

Experimental Site: A two-year field experiment was performed at the University of Massachusetts Agricultural Experiment Station Farm in South Deerfield, MA (42◦ N, 73◦ W) on fine Hadley loam soil. In both years, the experimental crops were grown after summer corn silage (*Zea Mays* L.) and winter fallow. The top 15 cm of soil was analyzed before cover cropping each year and the fields were amended with lime, sulfur, and potassium as recommended by the University of Massachusetts Soil and Plant Nutrient Testing Laboratory (Amherst, MA) for barley production. The experiment site was prepared using disk tillage immediately before the first planting date. Extreme weather events did not appear to influence the experiment in either year (Table 1).

**Table 1.** Weather Data for the experimental site in 2015 and 2016.


\* Average weather data from Amherst, MA—eight miles from South Deerfield. Averages are based on the years 2001–2020.

Experimental Layout: Four replications of each treatment were planted in a randomized complete block design, with cover crop species and barley seeding rate as fixed main effects. The 12 treatments consisted of balanced combinations of three barley seeding rates (300, 350, and 400 seeds m−2) and four summer cover crop species, including sunn hemp (SH), crimson clover (CC), sunn hemp and crimson clover (SH + CC), and summer fallow with no cover crop (NC).

Field Management and Assessments: Summer cover crops were planted on 19 July 2015 and 11 August 2016. The cover crops were planted at the following rates. SH: 33.6 kg ha−<sup>1</sup> sunn hemp, CC: 20.2 kg ha−<sup>1</sup> crimson clover, SH + CC: 16.8 kg ha−<sup>1</sup> sunn hemp and 16.8 kg ha−<sup>1</sup> crimson clover. Cover crop aboveground biomass was sampled from two 0.5 m2 sections on 8 September 2015 and 15 September 2016. Cover crop nitrogen content was calculated from crude protein using near-infrared spectroscopy (NIR) (Inframatic 8600, Perten Instruments). Cover crop biomass analysis included weeds growing with cover crops. Cover crops were flail mowed and terminated using a rototiller on 15 September 2015 and 16 September 2016.

Wintmalt, a 2-row malting barley, was planted on 25 September 2015 and 30 September 2016. Wintmalt is the common winter barley grown in New England. Cover crops and barley seeds were planted two cm deep, using a custom-made plot-size cone seed drill with 17.8 cm between rows.

Barley stands were counted on 16 October 2015 and October 2016. However, stand count data from 2016 was lost and the reported barley stand counts are based solely on data from 2015. Fall soil nitrate was measured immediately following the first hard frost on 20 October 2015 and 17 November 2016. Winter survival was not assessed in the spring of 2016 and was measured on 28 April 2017 using a 0–10 scale with 10 as complete survival and 0 as totally winter killed. Soil samples were collected to assess spring soil nitrate using five 6-inch-deep cores per plot, air dried, and soil nitrate content was determined using a LaChat QuickChem 8500 Series 2 Flow Injection Analysis System [31]. An amount of 28 kg ha−<sup>1</sup> nitrogen was applied as calcium ammonium nitrate on 15 April in both 2016 and 2017.

Foliar disease was estimated on 10 July 2017 as a percentage of leaf surface area infected using the disease guides in the American Phytopathological Society's ''A Manual of Assessment Keys for Plant Disease" [32]. Due to rapid drought-induced foliar desiccation, foliar diseases were not measured in 2016. Heading date was declared when half of the tillers had emerged heads and is reported as Julian date. Plant height was measured on 24 June 2016 and 10 July 2017 while lodging was assessed on 12 July 2016 and 10 July 2017. Lodging was visually evaluated on a 0–10 scale with 0 as no lodging and 10 as completely lodged.

Harvest and Laboratory Analyses: Barley was harvested on 19 July 2016 and 17 July 2017 using an ALMACO SPC20 plot combine. A subsample of the grain was dried in a forced air oven at 38 ◦C to preserve kernel integrity. Germinative energy, test weight, and 1000-kernel weight were determined using ASBC methods Barley–3A, Barley–2B, and Barley–2 [9]. 2017 grain samples could not be analyzed immediately following grain harvest and the samples had to be stored in a walk-in cooler for several years before analysis. As a result, germinative energy was considerably lower for these samples and, although their inclusion would not change the statistical results, they are not included in our results and analysis. Malting quality was assessed at the E.E. Cummings Crop Testing Laboratory at the University of Vermont (Burlington, VT). Crude protein content as a proportion of dry matter was measured with a Perten Inframatic 8600 Flour Analyzer, and falling number was assessed using the AACC Method 56–81B [33] on a Perten FN 1500 Falling Number Machine. DON content was evaluated in the subsamples using the NEOGEN Corp. Veratox DIN 2/3 Quantitative Test with a limit of detection of 0.1 mg kg<sup>−</sup>1.

Statistical Analysis: Data were analyzed using the permlmer and lmer functions in the predictmeans [34] and lme4 [35] packages of R statistical software [36]. Permutation tests were used to assess the impact of the main fixed effects of *cover crop type* and *barley seeding rate* as well as their interaction at a significance level of *p* ≤ 0.05. This non-parametric method was used to account for non-normal distribution of residuals and heterogeneous variance in many response variables. Bonferroni adjusted *t*-tests were used to make pairwise comparisons between all *cover crop type* treatments and orthogonal polynomial regression was used to assess the continuous effect of *barley seeding rate*. Because variance between groups was homogeneous, pooled standard deviations were used to calculate pairwise *t*-tests for *fall soil nitrate* and *barley grain falling number* while non-pooled standard deviations were used in the analysis of *cover crop biomass* and *cover crop nitrogen content* to account for heterogeneous variance. The random variables of *year* and *block* were combined into one random variable and data from both years were combined and analyzed collectively as eight replications.
