Running Title: Factors Influencing AYMT

Running title: Factors influencing AYMT

Factors influencing the agronomic performance of the Adapted Yam Minisett Technique in Nigeria – planting date and gender of the farmer

Stephen Morse (Corresponding author).

Centre for Environment and Sustainability (CES)

University of Surrey

Guildford, Surrey GU2 7XH

UK

Tel: +44(0)1483 686079

Fax: +44(0)1483 686671

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Nora McNamara

West Park

Artane

Dublin 5

Ireland

Tel/Fax +353 1 8187475

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Summary

This paper describes the results of three year’s data from farmers using the Adaptive Yam Minisett Technique (AYMT) to produce seed yams in Nigeria. A total of 30 sites were established each year between 2013 and 2015 in the Idah area (Kogi State) of Nigeria and 58 plots in the Amoke area (Benue State) in 2015. Each site had yam setts (80 to 100g) untreated and treated with a pesticide ‘dip’ prior to planting and farmers (male and female) were free to select the variety and manage the sites as they wished. In line with previous research the results suggest that treatment does increase the weight of tubers produced by a sett but not necessarily the number of tubers. Varietal differences were also observed. For the first time the results suggest that the time of planting does have a significant impact on seed tuber weight, with later planting leading to small tubers. Also, the gender of the farmer had an impact on some of the agronomic variables, with male owners of the site generally producing more and larger tubers per sett planted and sprouted than female owners. Various mechanisms for the latter are discussed in the paper.

Keywords: Yam, Dioscorea rotundata, clean seed, planting date, gender

Introduction

Yam (Dioscorea species; family, Dioscoreaceae) consists of over 600 species of which D. rotundata Poir (guinea yam, white yam), D. alata L. (water yam), D.cayenensis Lam. (yellow yam), D dumetorum Kunth (bitter yam) and D. esculenta Lour (lesser yam) are edible and cultivated on the largest scale. Yams are perennial species that produce underground ‘stem’ tubers that have meristematic tissue in loci (‘eyes’) close to the tuber surface and under the right conditions these can sprout. It is the yam tuber that is consumed following processing and cooking. This paper focuses on D. rotundata (white yam) and hence forth will be referred to as 'yam'. The yam tuber is rich in carbohydrate (75 to 85% of dry weight) and provides an excellent source of the B-complex group of vitamins, vitamin-A, beta carotene and some minerals (Muzac-Tucker et al., 1993) and the protein content varies between 2 and 5% on a dry weight basis (Alamu et al., 2014). As a result, it is thought that yam tubers provide excellent nutritional sustenance (Muzac-Tucker et al., 1993) and can be sold as a cash crop given its relatively high market price. These nutritional and market value attributes mean that yam can be an important crop for food security in West Africa (Verter and Becvarova, 2014; Mignouna et al., 2014). The crop also has cultural importance in a number of societies (Hahn et al. 1987). In Igbo culture (an ethnic group in the South East of Nigeria), for example, yam is perceived as a 'man's crop' as growing it is a symbol of strength which commands respect in society (Okeke et al., 2008).

The West African part of the yam belt accounts for some 95% of the global production of white yam (48 million tonnes), and Nigeria produces three quarters of the yams in West Africa (Shehu et al., 2010). D. rotundata is indigenous to West Africa and is especially widely grown in that part of the world, predominantly five countries; Benin, Côte d’Ivoire, Ghana, Nigeria and Togo (Asiedu and Sartie, 2010; Mignouna et al., 2014). A number of closely related species to D. rotundata can be found growing wild in Nigeria and to some extent domestication is still taking place (Vernier et al., 2003; Scarcelli et al., 2006). There are many cultivated varieties of white yam and this provides farmers with flexibility (Baco et al., 2008) although there is evidence that diversity is declining as farmers opt for varieties that best suit their local growing conditions and markets (Zannou et al., 2004).

Yams can primarily be propagated in the field and nursery via two main methods: (1) use of yam vine cuttings; and (2) Planting material derived from tubers – small whole tubers referred to as ‘seed’ yams so as to distinguish them from ‘ware’ yams (the tubers that are consumed) and cut pieces of a yam tuber referred to as setts. The use of vine cuttings has potential but has not yet been employed on a large scale (Asante et al., 2011) and in practice most farmers employ the use of tuber-derived material – either seed yams or setts – and it has been well established that multiplication ratios for yam are relatively low, ranging from 1:4 to 1:8 (Alvarez and Hahn, 1984), and shoot emergence tends to be uneven so that a field of planted seed yams or setts will have plants at various stages of growth (Otoo et al., 1987). Planting poor quality planting material can be assumed to impact on subsequent ware crop yield and tuber quality, and a recent paper suggests that under farmer-managed conditions the use of good quality seed yams can make a significant difference to ware yam yield (Morse and McNamara, in press) and unsurprisingly good quality seed yams sell for a premium price in markets (McNamara et al., 2012).

Researchers have sought to develop new ways of increasing the availability of good quality planting material, and these have often revolved around the use of small setts (minisetts) to generate seed yams. Ideally a farmer would need to produce seed yams approximately 0.25 to 1 kg in size (so called ‘Grade I’ seed yams; Ogbonna et al., 2011a and 2011b) but the sett size needed to produce this will vary depending upon factors such as variety and the environment (soil, rainfall, management practice etc.). The sett also needs to be treated with pesticide to ensure that the cut surfaces are not vulnerable to pest and disease attack (Morse and McNamara, 2015). One approach for generating seed yams is called the Adaptive Yam Minisett Technique (AYMT) and employs sett sizes of between 70 to 100g and a pesticide ‘dip’ (Morse et al., 2009; Morse and McNamara, 2015). While the economics of the AYMT have been explored along with the impact of factors such as pesticide treatment and yam variety (Morse and McNamara, 2015) there are other potentially important factors that have received no attention to date. One of them is the time of sett planting while the other relates to potential differences between seed yam plots owned by men and those owned by women. Yam is typically regarded as a ‘male’ crop in much of West Africa and men do the site preparation, ridging, planting, staking and harvesting, while women are typically involved in weeding, transportation and marketing. Women tend to hire men to work on their yam plots, but does this have an influence on output? Most of the information about such a difference between gender ownership of yam plots is anecdotal and based on discussions with farmers and there are few published studies. Omojola (2014) did find a statistically significant difference in the yields of male and female wetland farmers growing ware yam in the South West of Nigeria, with male yam farmers having greater yields than female farmers, but other studies have suggested no significant difference and there are few studies that have looked specifically at the impact on seed yam (Okeke et al., 2013; Okelola et al., 2014).

The research reported in this paper describes the results of ‘farmer-managed’ plots of AYMT established in Nigeria between 2013 and 2015. The primary purpose of these plots was to introduce farmers to the AYMT rather than undertake formal experiments. The intention was to allow them to experience AYMT first-hand, but the dates of management activities, yields and tuber numbers were recorded and fortuitously the farmers experimented with a range of planting dates over the three years to see how late they could plant. Also, as a number of the plots were owned by women it was possible to look for differences between male and female owned plots. Hence the focus of the paper will be on exploring the influence of planting date and gender of the plot owner on output variables from seed yams plots established with AYMT.

Materials and Methods

Research sites, treatments and design

AYMT demonstration sites were established between 2013 and 2015, with each site having two plots: one planted to untreated setts and one to setts treated with pesticide. The main location for the sites was the area surrounding the town of Idah (7°05′N; 6°45′E and population approximately 80,000), Kogi State, Nigeria, and 30 sites were established each year over that period. AYMT demonstrations were also established in 2015 in the area of Amoke town in Benue State, Nigeria (7°20′N; 8°45′E). Both Idah and Amoke are located in the middle belt of Nigeria (Supplementary Material Figure S1) and close to two main rivers (Niger and Benue), although Idah sits on the eastern bank of the Niger while Amoke is some miles inland. The soil in the Idah area is predominantly of the Fluvisol type (FL) while the area around Amoke is dominated by Alisols (AL) and Acrisols (AC).

The number of sites included in this study for both the Idah and Amoke areas are set out in Table 1, along with the gender of the named ‘owner’ of the plot, the number of setts planted in the untreated and treated plots and the varieties planted. The ‘owner’ of the site is defined as the person who ultimately has prime responsibility for its management and it is this person who receives the produce. Hence a woman may not own the land on which the plot is established, but she will be in charge of the management of the plot even if she does not become involved in any of the activities. Male owners do much of the work on their sites and visit it on a regular basis while the female owners, especially in the Idah area, typically hire men to do the bulk of the work for them.

<Table 1 near here>

All of the mother tubers used to generate the setts had already broken dormancy. Choice of yam variety was left for the farmer but given that the planting material was purchased for them it was necessary to have a degree of consensus where possible so that material could be sourced. In the Idah area during 2013 and 2014 some farmers wished to grow a variety called Ekpe while others preferred to grow Opoko (or Oboko). In 2015 the consensus shifted almost completely towards Akpaji (also called Ugah and Alumaco). In Amoke the consensus was entirely focussed on Ameh in 2015, a variety not popular in the Idah area although it is known to exist there.

The number of setts planted at each site was specified by the researchers and kept constant across all sites that year. Farmers were also encouraged to adopt the same spacing, typically between 2 and 3 setts planted per square metre (spacing of 35 to 50 cm between stands planted on metre ridges), and to use the same spacing for untreated and treated setts. Other than these requirements the management of each plot was left entirely for the farmer. Most of the sites were staked but the form of the staking (material used, height, spacing, trellising) was left for the farmer to decide. Plots were typically weeded twice, although some farmers used herbicide (pre and post-emergent) as a supplement to help keep the weed pressure down.

Each site had two plots: one smaller plot planted to untreated setts and one larger plot planted to treated setts. It should be noted that these were primarily intended as demonstrations rather than formal trials and that is the reason why the untreated areas were smaller than the treated areas. Treatment was via a 'pesticide dip' method described in Morse and McNamara (2015). The pesticides employed were Act Force Gold (insecticide; 45% w/w chlorpyrifos) and Z Force (fungicide; 80% w/w/ mancozeb). For every 10 litres of water a total of 100 ml of Act Force Gold (the insecticide; contains 45% of chlorpyrifos) and 100 g of Z-Force (the fungicide; contains 80% of mancozeb) were added. Setts were cut to the recommended size (80 to 100 g) and dipped into the pesticide solution before drying in the shade and planting. Planting and harvesting dates were chosen by the farmers and the months of planting are shown in Supplementary Material Table S1 and it is interesting to note how planting become later between 2013 and 2015 in Idah.

Data collection and analysis

The agronomic variables recorded for the untreated and treated plots at each site were as follows: (a) Sprouting rate (%): typically recorded around two months after planting; (b) Average tuber weight (kg): total weight of all tubers harvested divided by the number of tubers harvested; (c) Average weight of tubers per sett planted (kg): total weight of all tubers harvested divided by the number of setts planted; (d) Average number of tubers per sett planted: total number of tubers harvested divided by the number of setts planted; (e) Average weight of tubers per sett sprouted (kg): total weight of all the tubers harvested divided by the number of setts that had sprouted (typically around 2 months after planting); and (f) Average number of tubers per sett sprouted: total number of tubers harvested divided by the numbers of setts sprouted.

Dates of planting were recorded for each site and these were transformed into days with the 1st January each year being day 1. Analysis of the results was via multiple linear regression with dummy variables for treatment, variety and gender. Data from the Idah and Amoke areas were analysed separately, largely to avoid the confounding of location with variety. Only one yam variety was planted in the plots at Amoke, and while this variety is known to be present in the Idah area it was not one of their preferred varieties. Given that Idah and Amoke are different in a number of regards it was decided to analyse the data separately. The models for the two areas are as follows: