2.1 Interviews and focus group discussions

The four fields sampled are owned by two female members of the Mesopotamia group, with each member owning two of the fields. The two women that own the sampled fields and six other female members of Mesopotamia were interviewed to determine their agricultural knowledge and management choices. The eight women varied in age and experience (Table 1), capturing a broad spectrum of views and knowledge. The semi-structured interviews used open questions to determine what knowledge female farmers had about the effects of fertilizers on crops and soil, where they obtained this information, and the degree to which and with whom they shared this knowledge. A structured questionnaire was used for the interviews to gather complementary and comparable information on the women's knowledge and views. There were two themes incorporated in the interviews: fertilizer use and information gathering and use. The questionnaire can be found in the Supplement of this article, Supplement S1. The interviews were conducted with the assistance of an interview guide, including an introduction, opening questions, key questions, and a summary (adapted from Woodhouse, 1998; Curry, 2015a).

Table 1List of interview participants, including approximate age, number of fields (size between 0.1 and 1.5 acre – 0.04 and 0.6 ha), and farming experience in years.

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In addition to the interviews, two focus group discussions (FGDs) were held with members of the Mesopotamia group. One focus group discussion was held with six female participants and another with 11 participants, 6 women and 5 men. A women's only discussion was held with the six women participating to go more in depth into the knowledge of women, given that the aim of our study is to focus on female farmers as a group in its own right. The focus group discussions were based on questions used in the interviews and the methodology proposed by Curry (2015b), Krueger and Casey (2002), and Johnson and Mayoux (1998), which may be found in the Supplement of this article (Supplement S2). The discussions were aimed at determining the extent of agricultural knowledge in the Mesopotamia group as well as their information sources and the relative importance of these to the farmers. Both focus group discussions had the same format and started with a short opening and introduction followed by an explanation of the goal and guidelines for the discussion. The opening was followed by a set of discussion questions and an exercise. The discussion ended with a short summary by the discussion leader. Due to the open platform and the presence of multiple participants, the focus group discussions provided more in-depth answers and clarification to support and complement the information from the interviews.

2.2 Laboratory analyses and data processing

The soil samples were analyzed to determine how soil nutrient contents were influenced by the management choices of the female farmers. Water extracts of the soil samples were created (ratio of 1:2.5) and used to determine pH and electrical conductivity (EC). These water extracts were then filtered, and available P, K, S, Ca, and Mg were measured using a Perkin Elmer Optima 8000 ICP-OES Spectrometer. Available ${\mathrm{NH}}_{\mathrm{4}}^{+}$, ${\mathrm{NO}}_{\mathrm{3}}^{-}$, ${\mathrm{PO}}_{\mathrm{4}}^{\mathrm{3}-}$, and ${\mathrm{SO}}_{\mathrm{4}}^{\mathrm{2}-}$ in the extracts were determined on a Skalar SA-40 continuous-flow analyzer. Total organic and inorganic C in the extracts was measured using a Shimadzu TOC/TN analyzer.

Filtered BaCl₂ extracts were used for the determination of exchangeable Fe, Mn, Mg, Ca, Al, and K with ICP-OES (Schwertfeger and Hendershot, 2009). Extracts were prepared using 100 mL of BaCl₂, 0.125 M, and 4 g of a sieved and milled soil sample (< 2 mm). The cation exchange capacity (CEC) was calculated as the sum of the values for exchangeable Ca, Mg, K, and Na (in cmol_c kg⁻¹).

Total C and N were determined with 50 mg of soil (< 2 mm, milled) by using a Elementar Vario EL cube CNS analyzer. Total P, K, Ca, S, and Mg were determined by measuring HNO₃∕HCl extracts with ICP-OES; extracts were prepared with 250 mg of soil (< 2 mm, milled), 6 mL of HCl 37 %, and 2 mL of HNO₃ and underwent microwave destruction (60 min; T_max of 220 ^∘C; P_max of 75 bar). Total elemental composition of the soil samples was also determined using XRF analysis, using the Thermo Scientific XRF Analyzer Niton (setting: mining Cu∕Zn; Standard: NIST 2709a PP 180–649; 160 s).

Variance within each field and between fields with different management practices was determined using an analysis of variance (ANOVA) test. ANOVA was used in the case of normal data distribution, and the Kruskal–Wallis test was used with non-normal data distribution (Burt et al., 2009). The strength and direction of the relationship between different parameters was determined using a correlation coefficient, Pearson's r. All statistical analysis was done in MATLAB, version R2014b. The measured results and calculated variances were supported by the results of the interviews and focus group discussions.

3.1 Interviews

While the interviews started with investigating the typical daily activities, these turned out to vary too much from person to person and season to season to provide a meaningful clustering. The interviews did show that a range of agricultural management practices are known and practiced within the Mesopotamia group. Specifically, the agricultural management practices that the women spoke of during the interviews were crop rotation, fallow periods, fertilization with manure, compost and mineral fertilizer, intercropping, and mulching. Of the interviewees, two knew no other methods aside fertilization for improving the soil, three named mulching, four mentioned fallow periods, and four mentioned crop rotation. Three of the women found that they were limited in choice of management practice due to their socioeconomic circumstances. For example, for these women, fallow periods are not an option, as their lands are simply too small. A certain yield is needed for sufficient income generation, and leaving the land or a portion of it fallow would mean a significant reduction in income. A lack of fallow periods combined with intense agriculture puts pressure on the land, which can lead to increased erosion and may result in diminished soil nutrient content and yield (KNBS/AWSC, 2014).

Fertilizer use is mostly in the form of locally produced or homemade compost (four of eight interviewees) or the use of unprocessed cow manure (two of eight interviewees). The other two interviewees used either mineral fertilizer or cow manure with occasional application of mineral fertilizer. All interviewees named fertilizer as something that the soil needs for growing crops, but none really knew what fertilizer does for the soil in technical terms. The women indicated that their knowledge regarding the effects of fertilizer is limited to visible effects only. One explained that she fertilizes when the plants wilt slightly and the leaves start to yellow specifically. Six of the interviewees explained that they add extra fertilizer when their yields go down or when the plants grow less vigorously than usual, but two of these also mentioned other possible ways to increase production, like crop rotation or fallow periods. The agricultural information sources named during the interviews were relatives, including parents, grandparents, or husbands; training by NGOs or extension workers; elementary school; and observing others. Information from relatives was most common, being named by five of the interviewees, followed by training by NGOs or extension workers, named by three interviewees. As a point of interest, one of the interviewees got her information from her grandmother, who was also interviewed and who got her information from training by NGOs and extension workers. The agricultural knowledge women accumulate over their lifetime thus travels in small family and social circles.

To support the soil analysis, the two farmers, I2 and I7 (Table 1), whose fields were sampled, were interviewed more extensively than the other interviewees. Both farmers have at least 8 years of experience and principally grow kale. Both farmers use manure from cows and chicken mixed with organic waste. The farmer using only manure, I7, applies manure by plowing it into the soil at time of planting and then applies manure again every 4–12 weeks as she feels necessary. The farmer practicing intercropping, I2, applies manure as a topdressing at planting and approximately 8 weeks after planting. The cowpeas are broadcast on the field, and a number of the plants are removed after 2 weeks to make room for the kale to grow. Both farmers plow using a handheld tool, reaching a depth of approximately 20 cm. Farmer I7 weeds and plows her field every 10 d, whereas farmer I2 weeds every 14 d and plows her fields only every 26 weeks. In the fields of farmer I7, kale was grown in both fields in the previous growing season. The fields of the intercropping farmer were left fallow for 6 months before planting the current crops; in one of the fields maize was grown before the fallow period. Both farmers I2 and I7 use occasional fallow periods lasting between 3 and 6 months. Farmer I2 using intercropping started this practice in 2013 and has been using it ever since. Farmer I7, using manure application only, has been applying this practice for at least 5 years.

Both farmers had training by different NGOs and extension officers and incorporated this into their agricultural management, which led them to decide to use different practices. Farmer I2 indicated, however, that knowledge is often quickly forgotten due to a combined lack of use by the farmers and a lack of follow-up visits from the NGOs and extension officers. This was reflected by her own adaptation of the intercropping technique. She indicated that she relies on observation of her crops and experience to determine if fertilizer is required. As her crops continue to grow well, she did not feel the need to change her practices by plowing the cowpeas into the soil, which they call green manuring, or changing her fertilization practices. The farmer only using manure, I7, learned about the use of manure and creating compost from an NGO. She indicated that using manure is better than leaving the land fallow, as her crops continue to do well. The details of the sampled fields in terms of crops and management practices are provided in Table 2.

Table 2Details on the two farmers whose fields were sampled, with a description of their crops and agricultural management practice.

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3.2 Focus group discussions

During the women-only FGD we learned that most of the women work in the urban gardens as a way of generating income to provide for themselves and their children. At least half of the women participating in the FGD are widows, and agriculture is their sole form of income. They feel that their gender puts them at a disadvantage, as they feel that there is a lack of mutual understanding between the men and women of the group and that the men have a tendency to refuse to share resources with them. They believe that it would help if there would be at least one woman on the groups' board and that this would lead to more equal distribution of resources among the group members, such as fertilizers received from a local NGO. There are some limitations on the women's activity due to cultural restrictions, but not all of them are still actively followed. One limitation explicitly named during the women-only FGD still followed is the prohibition for women to plant and own trees. Banana trees, for example, can bring in higher profits than some other crops.

Much of the information from the interviews was confirmed in the focus group discussions. The exceptions were as follows. Although the types of fertilizers named during the FGD were mostly the same as those in the interviews, during the mixed FGD more of those responding appear to be using a form of mineral fertilizer. This discrepancy may be due to the inclusion of men in this FGD. It also became apparent during the mixed FGD that the farmers have knowledge of the way to work intercropping in a manner that can add N to the soil, in contrast to what was revealed from the interviews, but that they have a different name for this method: green manuring. During both FGDs and the interviews it was revealed that the management of the farms is largely reactionary. Decisions regarding using one of the various methods to restore soil fertility are undertaken only when the crops seem to do less well than previous crops.

While mineral fertilizers seem to be used more than inferred from the interviews, the participants of the FGDs show a preference for organic types of fertilizer. According to the Mesopotamia farmers, vegetables grown with organic fertilizers taste better and keep longer, whereas mineral fertilizer is reported to damage the soil.

When asked about the sources of agricultural information the participants of the mixed FGD named five different sources. All ranked family as the first and most important source, followed by training and demonstrations. Observation and visiting others was ranked third. Media and exhibitions were ranked fourth and fifth, respectively, and the farmers indicated that this is because of their lack of access to media and the expenses involved in visiting exhibitions. This may indicate that accessibility remains a problem for these farmers, even though there are more and closer sources of information on agricultural management in the urban environment.

3.3 Soil analysis

Intercropping is done by four of the women in the Mesopotamia group, mainly with cowpeas. Theoretically intercropping should improve soil nutrient content, specifically soil N content. However, the intercropping technique is not always applied in a way that would accomplish this: the cowpeas are harvested and not plowed into the soil. Plowing the cowpeas into the soil is needed for the nutrients accumulated to become available to other crops (Okalebo, 2009). The women also use intercropping to prevent soil erosion, while the main crop, often kale, is still growing. Intercropping also provides a source of income while the farmer waits for the kale to mature, as cowpeas mature faster.

The sampled soil was analyzed for its nutrient content and overall fell within the ranking “high” by FAO standards (FAO, 2006). Table 3 provides the average values of the main soil parameters for all four sampled fields as well as those parameters separated per management practice. The pH of the soil in the sampled fields ranged from neutral to very slightly alkaline, with an overall average of 7.3 (Table 3). The CEC was high overall, with an average value of 34.0 cmol_c kg⁻¹, likely as a consequence of the high clay content of the soil (Table 3). Similarly, with an average of 36.6 g kg⁻¹, the total soil carbon was also high. The laboratory analyses showed relatively high amounts of water-soluble and exchangeable cations; however there is a significant difference in nutrient content depending on the management practice.

Table 3Average pH; total C and N (g kg⁻¹); exchangeable Mg, Ca, K, and Na (mg kg⁻¹); CEC (cmol_c kg⁻¹); and water-soluble ions ${\mathrm{NO}}_{\mathrm{3}}^{-}$, NH⁴⁺, ${\mathrm{PO}}_{\mathrm{4}}^{-}$, and ${\mathrm{SO}}_{\mathrm{4}}^{\mathrm{2}-}$ (mg kg⁻¹) in the soil of Nyalanda field site overall for fields with manure application only and for fields with intercropping and manure application. Standard deviations in parenthesis (0–15 cm depth and four fields, with 12 samples per field; n=48).

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In the case of manure application combined with intercropping, the pH was neutral, whereas in the case of only manure application, the pH leaned towards being very slightly alkaline (FAO, 2006). The CEC was nearly 10 cmol_c kg⁻¹ higher in fields under only manuring than in the fields where there is also intercropping. Similarly, total soil carbon is nearly 20 g kg⁻¹ higher in the fields where only manure was applied in comparison with the fields where there was also intercropping (Table 1; Fig. 2a). There was no significant difference in soil organic carbon content between the intercropped and the manured fields (Fig. 2c). The contents of the macronutrients N, P, K, Ca, and Mg were almost all higher under the field management type manure application only, as compared to manuring combined with intercropping (Figs. 1 and 2).

Figure 1a, b, and c show the amounts of water-soluble and exchangeable Mg, Ca, and K as part of the total amount of the cation present in the soil, clearly demonstrating that the levels are higher under the practice of applying manure only. Figure 1d, e, and f show the proportion of the total amount of Mg, Ca, and K in the soil that is water-soluble or exchangeable. It is notable that under the practice of manure application combined with intercropping, the average exchangeable fraction for Mg and Ca and the average water-soluble fraction for Ca were higher even though the absolute amounts are higher under manuring only (Fig. 1). The Kruskal–Wallis and ANOVA tests showed that all the described differences between the fields and between the management practices were significant for these characteristics at a confidence interval of 95 %.

Figure 1(a, b, c) Bars length show the total, exchangeable, and plant available ∕ water-soluble amount of Mg, Ca, and K (in mg kg⁻¹) soil under management practices of manure and intercropping and manure. (d, e, f) Total, exchangeable, and plant available ∕ water-soluble Mg, Ca, and K in the soil as percentage of the sum.

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Figure 2Boxplots showing the differences between (a) total C (g kg⁻¹ soil), (b) C∕N ratio, (c) total organic C in the extracts (mg L⁻¹), (d) total N (g kg⁻¹ soil), (e) cation exchange capacity (CEC in cmol_c kg⁻¹), and (f) mineral N (mg kg⁻¹ soil) for the agricultural management practices of manure and intercropping and manure.

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