These in-depth interviews allowed us to ask the same questions of each farmer so that comparisons between interviews could be made. In person interviews were conducted in the winter, between December 2019 – February 2020; three interviews were conducted in December 2020. All interviews were recorded with permission from the farmer and lasted about 2 hours. To develop interview questions for the semi-structured interviews , we established initial topics and thematic sections first. We consulted with two organic farmers to develop final interview questions. The final format of the semi-structured interviews was designed to encourage deep knowledge sharing. For example, the interview questions were structured such that questions revisited topics to allow interviewees to expand on and deepen their answer with each subsequent version of the question. Certain questions attempted to understand farmer perspectives from multiple angles and avoided scientific jargon or frameworks whenever possible. Most questions promoted open ended responses to elicit the full range of possible responses from farmers. We used an openended, qualitative approach that relies on in-depth and in-person interviews to study farmer knowledge . In the semi-structured interview, farmers were asked a range of questions that included: their personal background with farming and the history of their farm operation, their general farm management approaches, as well as soil management approaches specific to soil health and soil fertility, such as key nutrients in their consideration of soil fertility, and their thoughts on soil tests . A brief in-person survey that asked several key demographic questions was administered at the end of the semistructured interviews. Interviews were transcribed, reviewed for accuracy, cannabis growing system and uploaded to NVivo 12, a software tool used to categorize and organize themes systematically based on research questions .

Through structured analysis of the interview transcripts, key themes were identified and then a codebook was constructed to systematically categorize data related to soil health and soil fertility . We summarize these results in table form.To unpack differences between Fields A and Fields B across all farms, we applied a multi-step approach. We first conducted a preliminary, global comparison between Fields A and Fields B across all farms using a one-way analysis of variance to determine if Fields A were significantly different from Fields B for each indicator for soil fertility. Then, to develop a basis for further comparison of Fields A and Fields B, we considered potential links between management and soil fertility. To do so, we developed a gradient among the farms using a range of soil management practices detailed during the initial farm visit. These soil management practices were based on interview data from the initial farm visit, and were also emphasized by farmers as key practices linked to soil fertility. The practices used to inform the gradient included cover crop application, amount of tillage, crop rotation patterns, crop diversity, the use of integrated crop and livestock systems , and the amount of N-based fertilizer application. Cover crop frequency was determined using the average number of cover crop plantings per year, calculated as cover crop planting counts over the course of two growing years for each field site. Tillage encompassed the number of tillage passes a farmer performed per field site per season. To quantify crop rotation, a rotational complexity index was calculated for each site using the formula outlined by Socolar et al. . To calculate crop diversity, we focused on crop abundance, the total number of crops grown per year at the whole farm level was divided by the total acreage farmed.

To determine ICLS, an index was created based on the number and type of animals utilized . Lastly, we calculated the amount of additional N-based fertilizer applied to each field . In order to group, visualize, and further explore links with indicators for soil fertility, all soil management variables were standardized , and then used in a principal components analysis using the factoextra package in R . In short, these independent management variables were used to create a composite of several management variables. Principal components with eigenvalues greater than 1.0 were retained. To establish the gradient in management, we plotted all 13 farms using the first two principal components,and ordered the farms based on spatial relationships that arose from this visualization using the nearest neighbor analysis . To further explore links between management and soil fertility, we used the results from the PCA to formalize a gradient in management across all farms, and then used this gradient as the basis for comparison between Field A and Field B across all indicators for soil fertility. Using the ggplot and tidyverse packages , we displayed the difference in values between Field A and Field B for each indicator for soil fertility sampled at each farm using bar plots. We also included error bars to show the range of uncertainty in these indicators for soil fertility. Lastly, we further compared Field A and Field B for each farm using radar plots. To generate the radar plots, we first scaled each soil indicator from 0 to 1. Using Jenks natural breaks optimization, we then grouped each farm based on low, medium, and high N-based fertilizer application, as this soil management metric was the strongest coefficient loading from the first principal component . Using the fmsb package in R , we used an averaging approach for each level of N-based fertilizer application to create three radar plots that each compared Field A and Field B across the eight indicators for soil fertility.Farmer responses for describing key aspects of soil health were relatively similar and overlapped considerably in content and language . Specifically, farmers usually emphasized the importance of maintaining soil life and/or soil biology, promoting diversity, limiting soil compaction and minimizing disturbance to soil, and maintaining good soil structure and moisture.

Several farmers also touched on the importance of using crops as indicators for monitoring soil health and the importance of limiting pests and disease. Discussion of the importance of promoting soil life, soil biology, and microbial and fungal activity had the highest count among farmers with ten mentions across the 13 farmers interviewed. Next to this topic, minimizing tillage and soil disturbance was the second most discussed with six of 13 farmers highlighting this key aspect of soil health. The importance of crop health as an indicator for soil health also surfaced for five out of 13 farmers. In addition to discussing soil health more broadly, farmers also provided in-depth responses to a series of questions related to soil fertility—such as key nutrients of interest on their farm, details about their fertility program, and the usefulness of soil tests in their farm operation— summarized in Table 2. When asked to elaborate on the extent to which they considered key nutrients, a handful of farmers readily listed several nutrients, including nitrogen, phosphorous, potassium , and other general macronutrients as well as one micronutrient . Among these farmers that responded with a list of key nutrients, some talked about having their nutrients “lined up” as part of their fertility program. This approach involved keeping nutrients “in balance,” such as for example, monitoring pH to ensure magnesium levels did not impact calcium availability to plants. These farmers also emphasized that though nitrogen represented a key nutrient and was important to consider in their farm operation, flood table tracking soil nitrogen levels was less important than other aspects of soil management, such as promoting soil biological processes, maintaining adequate soil moisture and aeration, or planting cover crops regularly. As one farmer put it, “if you add nutrients to the soil, and the biology is not right, the plants will not be able to absorb it.” Or, as another farmer emphasized, “It’s not about adding more [nitrogen]… I try to cover crop more too.” A third farmer emphasized, that “I don’t use any fertilizers because I honestly don’t believe in adding retroactively to fix a plant from the top down.” This same farmer relied on planting a cover crop once per year in each field, and discing that cover crop into the ground to ensure his crops were provided with adequate nitrogen for the following two seasons. While most farmers readily listed key nutrients, several farmers shifted conversation away from focusing on nutrients. One farmer responded, “I’m not really a nutrient guy.” This same farmer added that he considered [soil fertility] a soil biology issue as much as a chemistry issue.” The general sentiment among these farmers emphasized that soil fertility was not about measuring and “lining up” nutrients, but about taking a more holistic approach.

This approach focused on facilitating conditions in the soil and on-farm that promoted a soil-plant-microbe environment ideal for crop health and vigor. For example, the same farmer quoted above mentioned the importance of establishing and maintaining crop root systems, emphasizing that “if the root systems of a crop are not well established, that’s not something I can overcome just by dumping more nitrogen on the plants.”Another farmer similarly emphasized that they simply created the conditions for plants to “thrive,” and “have pretty much just stepped back and let our system do what it does; specifically, we feed our chickens whey-soaked wheat berries and then we rotate our chickens on the field prior to planting. And we cover crop.” A third farmer also maintained that their base fertility program—a combination of planting a cover crop two seasons per year, an ICLS chicken rotation program, minimal liquid N-based fertilizer addition, and occasionally compost application—all worked together to “synergize with biology in the soil.” This synergy in the soil created by management practices—rather than focusing on nutrient levels—guided this farmer’s approach to building and assessing soil fertility on-farm. Another farmer called this approach “place-based” farming. This particular farmer elaborated on this concept, saying “I think the best style of farming is one where you come up with a routine [meaning like a fertility program] that uses resources you have: cover crops, waste materials beneficial to crops, animals” in order to build organic matter, which “seems to buffer some of the problems” that this farmer encountered on their farm. Similar to other farmers, this farmer asserted that adding more nitrogen-based fertilizer did not lead to better soil fertility or increase yields, in their direct experience. Regardless of whether farmers listed key nutrients, a majority of farmers voiced that nitrogen was not a big concern for them on their farm. This sentiment was shared among most farmers in part because they felt the amount of nitrogen additions from fertilizers they added were insignificant compared to nitrogen additions by conventional farms. Farmers also emphasized that the amount of nitrogen they were adding was not enough to cause environmental harm; relatedly, a few farmers noted the absurdity and added economic burden of the recent nitrogen management plan requirements—specifically among organic farms with very low N-based fertilizer application. The majority of farmers also expressed that their use of cover crops and the small amount of N-based fertilizer additions as part of their soil fertility program ensured on-farm nitrogen demands were met for their crops. Across all farmers interviewed, cover cropping served as the baseline and heart of each fertility program, and was considered more effective than additional N-based fertilizers at maintaining and building soil fertility. Farmers used a range of cover crop species and often applied a mix of cover crops, including vetches and other legumes like red clover and cowpea , grains and cereals like oats . Farmers cited several reasons for the effectiveness of cover cropping, such as increased organic matter content, more established root systems, greater microbial activity, better aeration and crumble in their soils, greater number of earthworms and arthropods, improved drainage in their soils, and more bio-available N. Whereas farmers agreed that “more is not better” with regards to N-based fertilizers, farmers did agree that allocating more fields for planting cover crops over the course of the year was beneficial in terms of soil fertility. However, as one farmer pointed out, while cover crops provide the best basis for an effective soil fertility program, this approach is not always economically viable or physically possible.Several farmers expressed concern because they often must allocate more fields to cover crops than cash crops in any given season, which means that their farm operation requires more land to be able to produce the same amount of vegetables than if they had all their fields in cash crops.