Monitoring Changes in the Cultivation of Pigeonpea and Groundnut in Malawi Using Time Series Satellite Imagery for Sustainable Food Systems

Abstract

Malawi, in south-eastern Africa, is one of the poorest countries in the world. Food security in the country hinges on rainfed systems in which maize and sorghum are staple cereals and groundnut and pigeonpea are now major grain legume crops. While the country has experienced a considerable reduction in forest lands, population growth and demand for food production have seen an increase in the area dedicated to agricultural crops. From 2010, pigeonpea developed into a major export crop, and is commonly intercropped with cereals or grown in double-up legume systems. Information on the spatial extent of these crops is useful for estimating food supply, understanding export potential, and planning policy changes as examples of various applications. Remote sensing analysis offers a number of efficient approaches to deliver spatial, reproducible data on land use and land cover (LULC) and changes therein. Moderate Resolution Imaging Spectroradiometer (MODIS) products (fortnightly and monthly) and derived phenological parameters assist in mapping cropland areas during the agricultural season, with explicit focus on redistributed farmland. Owing to its low revisit time and the availability of long-term period data, MODIS offers several advantages, e.g., the possibility of obtaining cloud-free Normalized Difference Vegetation Index (NDVI) profile and an analysis using one methodology applied to one sensor at regular acquisition dates, avoiding incomparable results. To assess the expansion of areas used in the production of pigeonpea and groundnut resulting from the release of new varieties, the spatial distribution of cropland areas was mapped using MODIS NDVI 16-day time-series products (MOD13Q1) at a spatial resolution of 250 m for the years 2010–2011 and 2016–2017. The resultant cropland extent map was validated using intensive ground survey data. Pigeonpea is mostly grown in the southern dry districts of Mulanje, Phalombe, Chiradzulu, Blantyre and Mwanza and parts of Balaka and Chikwawa as a groundnut-pigeonpea intercrop, and sorghum-pigeonpea intercrop in Mzimba district. By 2016, groundnut extent had increased in Mwanza, Mulanje, and Phalombe and fallen in Mzimba. The result indicates that the area planted with pigeonpea had increased by 29% (75,000 ha) from 2010–2011 to 2016–2017. Pigeonpea expansion in recent years has resulted from major export opportunities to Asian countries like India, and its consumption by Asian expatriates all over the world. This study provides useful information for policy changes and the prioritization of resources allocated to sustainable food production and to support smallholder farmers.

Land Cover Classification of Nine Perennial Crops Using Sentinel-1 and -2 Data

“…Analysis of the location and area of crops facilitates water resource planning [5]. A better understanding of the temporal and spatial distribution of specific crop types can greatly assist in monitoring production spread and improve decision-making around varietal selection [6], harvest planning and decisions on spray application based on risk to neighboring crops and wildlife [7]. Accurate measures of a crop area are also essential when estimating annual gross production [8].…”

Assessment of land use change in the Thuma forest reserve region of Malawi, Africa

“…The images were downloaded from the United States Geological Survey website (GloVis). We specified the time of the imagery concentration on summer months because that is the time to obtain clear images for Malawi (Gumma et al 2019). Cloud cover was specified from 0 to 10%.…”

“…The validation samples were collected for the year 2017. The samples were randomly selected in a Stratified Random Sampling based on accessibility (along the roads/paths) of the study area and location homogeneity (Gumma et al 2019). They were generated in ArcMap and were converted to GPX format and uploaded in a Geographic Positioning System (GPS) device which was then used to locate the sampled points on the ground.…”

Who does what and why? Intra-household roles and explanatory models for sourcing soybean seed from the formal sector in Malawi

“…The sector creates jobs for nearly 90% of the employed working age population (15-64 years) in Malawi (Baulch et al, 2019). The farming system is dominated by maize (Zea mays L.), which according to some sources, is grown by 97% of farming households on at least 60-80% of the total cultivated land (Bezner Kerr, 2012;Gumma et al, 2019;White, 2019). The lack of crop diversification in the country's farming system is evident in the estimated agricultural production figures produced by the Government each year (see Ministry of Agriculture, Irrigation and Water Development, 2017).…”