Maize is an important food and fodder crop in many countries (Cadoni and Angelucci, 2013). It ranks third globally in terms of production after rice and wheat. Nigeria is the second leading producer of maize in Africa but despite its high production, Nigeria’s average maize yield is still among the lowest in the world.

Experts have reported that Nigeria could become the largest maize producer in Africa and one of the largest producers in the world without increasing the area under cultivation (SAHEL, 2017).

The majority of maize producers in Nigeria are smallholder farmers (male and female) producing more than 70% of the nation’s maize. There are only a few large-scale producers (GIZ, 2013). Cultivation is highest in the northern part of the country especially in the states of Kano, Kaduna, Bauchi, Gombe, Adamawa, Taraba and Jigawa (BRIU, 2015).

In 2013, Kano and Kaduna states produced 12.1% of national maize supply (GIZ, 2013). Among the South western states,  Ogun,  Ondo  and  Oyo  are  the  leading producers of maize (SAHEL, 2017). The national requirement for maize is estimated at about 16 million tons, with the production of 10.3 million MT in 2013, supply deficit is about a shortfall of 5.7 million MT (NAERLS, 2014). 

Since the report on Global Food Losses and Food Waste (FAO, 2011) reported that 1/3^rd of all foods were being lost, and the World Bank (2011) “Missing Foods” report on storage losses of grains in Africa, many new reports have been published on the topic (APHLIS, 2014). 

The many postharvest loss studies and crop loss assessments that have been published in recent years often use ad hoc measurements, survey questionnaires or interviews, and focus on measuring overall quantitative (physical, volume or weight) losses (APHLIS, 2014). Each researcher has developed their own data collection instruments for different crops and target populations, and has reported on recall of % losses or weight losses for the crop, generally reported as estimates or ranges. PHL data is rarely available on the quantitative losses being experienced at the different levels of the value chain, standard deviations for reported loss levels, characteristics of qualitative losses, value of economic losses or other parameters related to food security such as nutritional losses. 

Affognon et al. (2015) reviewed postharvest loss reports generated in some African countries and found out most had to be eliminated because they provided unreliable data. Affognon et al (2015) further found out that most of the available historical data was focused on storage weight losses for maize and therefore recommended expanding future postharvest loss assessment studies. APHLIS (2015) reported the estimated postharvest losses of maize in Nigeria according to states.

The objectives of the CSAM study were to identify and quantify the main causes and sources of food loss in the postharvest chain from the harvest to the retail market in major maize production states of Kano and Ogun. The analysis identifies where farmers and traders are losing the most quantity, quality and economic value, and identifies appropriate interventions for reducing these losses.

 

The field work for this study was conducted between July and August, 2017 in Kano and Ogun states using Commodity Systems Assessment Methodology (CSAM), recently updated by postharvest trainers at IICA and PEF (LaGra et al., 2016). The study was done as part of an Agribusiness Associates Inc. project funded by the World Bank Group.

A CSAM study begins with a literature review of published articles and unpublished documents, review articles and government reports. CSAM is a systematic process of using survey questions, interviews, observations and field measurements to collect data on the key aspects of the value chain, including preproduction, production, postharvest handling and marketing. It considers the entire commodity system, from planning and production to processing and marketing, but focuses heavily on the postharvest and marketing aspects in order to determine the relative costs and benefits of any potential or observed changes in handling practices, containers, value addition or marketing practices.

For this study, data on the maize value chain was collected via literature review, interviews following a simplified set of written questions targeted to the crop, observations of the harvest and postharvest handling practices, and direct measurements in the field. Questions related to production were asked mainly to farmers; traders and marketers were asked about postharvest handling and marketing and researchers, project staff and/or extension workers were questioned about the entire commodity system. CSAM interviews were conducted with 10 to 15 persons via a stratified sample of known crop experts, extension workers, farmers, traders, storage operators, processors and marketers. 

Additionally, the field teams utilized standardized worksheets for on farm, storage, wholesale and retail market data collection on postharvest losses, quality characteristics, market value changes, and a worksheet on the costs/benefits of potential changes in practices. The general process of the field-based assessment was to sample postharvest losses for a random selection of 10 farms, 10 storage facilities, 10 wholesale markets and 10 retail marketing sites via direct measurements, questions and observations. 

Tools used during the CSAM studies included: Digital scale (5 kg capacity); hanging scale (30 kg capacity); digital temperature probe; digital camera; digital hygrometer and set of data collection worksheets with protocols.

Data collection measurements are designed to be simple and non-destructive whenever possible. For example, quality characteristics are determined via sorting a random sample of 20 cobs or kernels into pertinent categories (defects, appearance, damage, decay, etc.). The undamaged maize can then be returned to the farmer or vendor.

Data analyses are likewise kept as simple as possible when conducting a CSAM study. Data entry is via a simple spreadsheet that matches the data collection worksheets, and requires calculations of sums, ranges, averages and standard deviations.

 

The following is a summary of the key findings on maize postharvest losses and overall results of the CSAM studies (Tables 1 and 2). 

 

 

Cultural practices

The cultural practices for maize production vary from one region to another in Nigeria and this affect the quality and quantity of the commodity produced. During field visits in Ogun state, the team observed that the majority of farmers do little or no fertilization at all, unlike in Northern part of Nigeria where maize is believed not to do well without fertilizer. The harvested crops were mostly unsorted and so farmers were largely unaware of any postharvest losses.  Harvest losses can be due to missing produce on the plant, dropping cobs in the field, and discards due to obvious pest damage. 

Maize is dried in the sun on the farm prior to sale.

Quality at harvest (defects, decay and/or damage), size of cobs and moisture content all affect farm gate prices.The yield of maize for the farms in Ogun State visited during this study was higher than the national average. The farm gate price is determined by the number of cobs or by the volume sold, and the moisture content, but maize is not sold by weight. Maize losses at wholesale markets

The assessment was done in the Kano area in Northern Nigeria, as this is the major maize wholesale, storage and retailing area while assessment of fresh cobs wholesale was done in Ogun state. Containers are standard 100 kg sacks for maize kernels while reuse old fertilizer or rice sacks for packaging maize cobs. A few small-scale wholesalers do shelling and/or cleaning as a value addition practice, using manual methods. Marketers complain about being at the mercy of middlemen regarding market prices.

Maize losses in storage

The assessment was done in the Kano area in Northern Nigeria, as this is the major maize wholesale, storage and retailing area. One of the ten storage facilities assessed offered storage in a well-ventilated metal silo.  The standard sized sack was 100 kg of kernels.  The storage period had a range of 5 to 10 months (for kernels) or 4 to 9 months (for the few who stored maize as cobs).

Maize losses at retail markets

The assessment was done in the Kano area in Northern Nigeria, as this is the major maize wholesale, storage and retailing area. There was no grading or pricing by quality grade at the retail level, but sometimes cleaning was done to remove debris. Damage or defects (especially small sizes) was related to reduce prices, but there were little or no reports of discards.

Percent postharvest losses and discarded maize

Postharvest losses (PHLs) measured in Nigeria on farm ranged from 7 to 23% (average 13%) loss or discarded during the harvest. Sorting discards at the storage and wholesale levels were low to none, and mechanical damage in the assessed samples was 2 to 3.5% quality loss.  At the retail level, there was no sorting. PHLs cannot simply be added across these value chain stages, due to the very wide range of losses measured in each sample. If the minimum levels of the range of measured PHLs are added up for the farm, storage, wholesale and retail sites, the total is 15%, which is the most conservative estimation of overall losses (Table 4).

On the 10 farms, the field team was able to collect and weigh the total amount of maize harvested, and collect and weigh the maize left in the field after the harvest. Based upon the average weight collected from 3 sample plots on each farm, 646 kg/ha was either left on the plants or discarded on the ground in the field. Therefore, the PHLs during the harvest was 13% of the total estimated harvest of 5 MT/ha. Lost or discarded maize was typically used for animal feed.

Postharvest quality and food safety

Maize quality characteristics were assessed during the CSAM studies, and found to be closely related to market value. Typical quality issues on the farm included: 1) Defects: unfilled cobs, darkening, shrivel, misshapen kernels, small kernels; 2) decay: fungi/mould and damage: mechanical injury, cracks, pest damage (army worms, weevils, stray animals).

During harvesting, maize was left in the open field under direct sunlight and during humid weather until harvesting is completed, thereby heating up the produce. Temperature is the most important environmental factor that influences the rate of deterioration of harvested produce. High temperatures recorded in Table 3 during harvest, storage and retailing will therefore reduce potential storage life. Most of the decayed maize was sorted out at the farm level and so does not reach the markets. The sacks used for maize transport are large and heavy. The farmers and traders do not weigh the full woven sacks, but generally estimate the sack as equal to hold 100 kg.

 

 

 

There is no local, regional or national standard for quality inspection carried out on farms and markets in the study area. Farmers farming practices had tremendous effects on the quality of the produce. The quality of maize

seeds used for planting by farmers in the study area was generally poor. They made use of seeds saved from their previous harvest, and replant each year without using improved seeds. These seeds have lost vigour and good quality characteristics with time.                             

Estimated value of postharvest losses of maize in Nigeria

If the maize crop in Nigeria is experiencing a conservative 15% loss in terms of quantity during the farm to market period, this equates to a loss in market value of at least 15%. If the annual production of maize is 10.8 million MT, at an average market value of N160/kg, 15% PHLs equate to a loss in potential market value of $720 million per year (Tables 5 and 6). 

 

 

2) Aggregation is time consuming and costly, contributing to low farm prices.

3) Farmers lack information about prices in nearby markets and also lack cost-effective means of transporting maize individually.

4) Low levels of trust between farmers may limit collective sales or transportation.

Improper drying and lack of grades

1) Maize is often not fully dried at the farm nor is it fumigated, resulting in the need for further drying and sometimes fumigation by traders.

2) The amount of sorted out maize is higher if the harvest occurs during a rainy time (USAID 2012).

3) The absence of standardized grades requires the quality of produce to be manually checked. As a result of both of these factors, maize is repeatedly packed and unpacked during marketing, creating inefficiencies in the market chain.

4) Poor drying at initial stages in the marketing chain can result in high levels of aflatoxins (which cannot be visually observed).

Costs and benefits of improved practices and technologies for maize

A few recommended postharvest technologies for reducing losses in maize include:

1) Use of maturity indices during harvesting. In Nigeria, maize is harvested at various stages of moisture, which can lead to losses due to kernels dropping off (too dry) or to mouldiness (too wet).  The offered farm gate prices will be lower than the potential market value of higher quality maize.

2) Use of improved storage bags. In Nigeria, Purdue Improved Crop Storage (PICS) bags, used for hermetic storage of maize and dry beans, are much more expensive than traditional woven polypropylene storage bags.   “Imitation PICS” are available at a lower price, but their effectiveness is unknown. The PICS bags  are  triple layered, made with a layer of solid plastic to seal out air in order to asphyxiate any insect pests that may be inside the bag of grain. Their use for maize storage in Kano can result in a small but immediate profit, regardless of the market price.  If taken care of between uses, PICS bags can be reused for grain storage at least one more time, and they can keep maize safe from pests during a storage period of up to one year. Table 7 provides details on cost and benefits of using PICS bags for maize storage in Kano State, Nigeria.

 

 

Deterioration of maize is mainly affected by moisture content, temperature (grain and air), relative humidity, storage conditions, fungal growth, and insect pests (Suleiman et al., 2013). Exposure to higher RH after harvest can increase moisture content and this will negatively influence the physical and sanitary quality of maize (José et al., 2017). Presented in Table 3 are postharvest system characteristics for maize in Nigeria. Grain moisture content is among the most important factors that influence time needed for preservation as well as the whole health status of maize grain (Andrade et al., 2017; Bhandari et al., 2017; Mirna et al., 2007). High moisture level during harvest, storage and retailing is unfavourable and can minimize preservation ability of the grain.

Intensive respiration process prior to drying enables activities of microorganisms, and produce favourable medium (temperature raise, moisture raise and heat release) for storage pests (Volenik et al., 2007).

Polypropylene bags used for maize packaging in Nigeria provide poor protection during storage and this contributes to huge postharvest losses. Proper drying and use of hermetic packaging system were reported to provide good keeping quality after year storage under ambient storage conditions (Gopal et al., 2017).

 

 

 

 

 

The defects can be influenced by combination of high temperature and relative humidity, and poor transportation and storage system

Maize postharvest losses on Nigerian farms were found to be 13% (average). Mechanical damages during handling, transportation and transportation account for 2 to 3.5% quality loss in dried maize. An average of 15% loss was recorded across the value chain. If the annual production of maize is 10.8 million MT, at an average market value of N160/kg, 15% PHLs equate to a loss in potential market value of $US 720 million per year. 

Training farmers on the importance of using improved varieties, modern farming practices, understanding and applying the knowledge of maturity indices, good postharvest management, and use of improved containers and modern storage systems will minimise losses at all levels along the value chain.

 

The authors have not declared any conflict of interests.