Perenniality in mixed cropping systems is rarely an agronomic subject, as is demonstrated by comparatively modest research on the breeding of perennial grains (Kane et al. 2016) and on permaculture (Ferguson and Lovell 2014). In reality, small farmers around the world already resist simplified models of agriculture by diversifying their farms (Altieri 2004; Altieri and Toledo 2011). The central motivation of our review is to consider options for shifting agronomic research from models focused on monoculture production of short duration crop types toward those focused on the integration of perennial and annual species in mixed cropping systems.
The cultivation and wild harvesting of perennial foods is a historic legacy and a present-day strategy in some regions of Sub-Saharan Africa (see Harlan 1989a, b; NRC 1996; Batello et al. 2004, 2014). For the purposes of this article, we consider crops that may be managed to produce harvests for more than one rainy season as exhibiting perennial attributes. These attributes are present in several important African food crops such as sorghum (Sorghum bicolor [L.] Moench), pigeonpea (Cajanus cajan [L.] Millsp.), and cassava (Manihot esculenta). Our interest is primarily in perennial grains, but we include cassava because it is commonly grown for more than one rainy season.
Our study begins with a review of the literature on ratooning pigeonpea and sorghum. Ratooning is the cultural practice of cutting crops near their crown after a first harvest of grain or fodder (Fig. 1). This permits crops such as sorghum, pearl millet, and pigeonpea to grow back for subsequent harvests of grain or animal forage (NRC 1996). We also discuss the historic contributions of perennial attributes to environmental sustainability and food security in Malawi. In order to strengthen the limited research on ratooning generally and on the role of perenniality in Malawian food systems, we reflect on interviews with Malawian farmers about the use of perennial staple crops under largely rainfed and marginal conditions. Are perennial staple crops grown in particular agricultural environments or under certain social contexts? In comparison with annuals, perennials may exhibit different pests and diseases, market potential, timing of production, and spatial arrangements. We highlight how perennial staple crops already contribute to the agricultural objectives of Malawian farmers. Finally, we discuss opportunities for action and research to develop the potential of perennial staple crops.
A review of the literature on ratooning
There is little research on the cultural practice of ratooning sorghum and pigeonpea. A search of four prominent bibliographic databases retrieved 66 relevant references on the ratooning of sorghum and 20 relevant references on the ratooning of pigeonpea. Kane et al. (2016) explain how this search was conducted. Of the references whose location could be determined, the majority of research on ratooning sorghum and pigeonpea came from India (40 and 81 %, respectively; Table 1). The United States and Australia have contributed some research on ratooning sorghum (22 and 9 %, respectively). Very little research on ratooning sorghum and pigeonpea comes from the African continent (9 and 19 % respectively) even though Africa is a center of diversity for these crops. We begin by reflecting on the primary issues and research findings globally given limited prior research. Later sections present a research agenda on perennial staple crops for the southern and eastern Africa region that includes the important cultural practice of ratooning.
Breeding and selection of sorghum for ratooning systems is sparse. The earliest scientific literature on ratooning has promoted it as a method used for seed selection of outcrossed seed stock (Parmornchantr 1966). It was not until the 1980s that tiller regrowth of a ratoon crop was used as a measure of non-senescence and was found to be quantitatively inherited with additive genetic effects and no indication of significant dominance genetic effects (Duncan et al. 1980). More recently, the genes commonly expressed in rhizomes were identified to find possible relatedness between rhizomatous and ratooning quantitative trait loci that may be a result of ancient duplication (Jang et al. 2006). Areas highlighted for breeding include ratoon cultivar types with pest resistance and with increased plant weight production of the ratoon crop (Duncan and Gardner 1984). Although varietal adaptability is important (Goodroad and Duncan 1988), breeding efforts to stabilize ratoon crop yields may even be more so (Duncan and Moss 1987). Early duration varieties may help the ratoon crop avoid drought (Bapat and Shinde 1978), but medium-maturity sorghum hybrids have been found to out-yield the early group by 2.70 t grain/ha and the late group by 1.90 t grain/ha (Duncan 1979). Only one study found that planting sorghum hybrids out-yielded ratooned sorghum in terms of grain and fodder over a three year period (Gaikwad et al. 1984).
Ratooning sorghum is primarily a water management strategy in southern and eastern Africa. In Ethiopia, a center of origin and diversity for sorghum, 30 % of farmers practiced ratooning mostly due to drought (71 %), but also pests (26 %; Mekbib 2009). Studies have shown that ratooned sorghum has high production stability in both below and above average rainfall years under semi-arid conditions (Brahmbhatt and Patel 1983). This perspective runs contrary to the hydrologic and crop growth models of ratooned grain sorghum in the Central Texas Badlands that predicted inadequate yields with normal water levels (Stinson et al. 1981). These water shortfalls for ratooned sorghum production might be mitigated by recommendations from agronomic research on critical stages for irrigation to ensure optimal yields and high water use efficiency (Patel et al. 1989), such as at flowering (Subramanian et al. 1986).
Diseases, such as the fungus Colletotrichum graminicola (Bergquist 1973), and insect pests, such as the fall armyworm (Spodoptera frugiperda Smith; Duncan and Gardner 1984), appear to be more severe on ratoon sorghum. For example, a study in India found that Atherigona soccata (Rond.) caused particularly substantial losses of grain and fodder in the ratoon crop (Mote et al. 1982). The only abundant pest of sorghum identified by Mote (1983) was A. soccata, which caused the most losses in grain and fodder production for the ratoon crop in comparison to the rainy season and winter crops. More specific to our region of interest, stem borer Chilo partellus (Swinhoe) has expanded its range in the low-altitude regions of eastern and southern Africa since its first detection in 1932 in part because of its efficiency in colonizing ratooned sorghum, thus outcompeting the stem borer Busseola fusca (Fuller) that was already present in the region (Kfir 1997). In South Africa, the first generation of C. partellus was found to only infest early grain sorghum tillers from a ratoon crop (Kfir 1992). Larval parasitism, mostly by Cotesia sesamiae, usually lags behind the peak larval population of even the native B. fusca in the ratooned sorghum crops of South Africa (Kfir and Bell 1993).
Management choices appear to greatly influence the grain yields from ratooned sorghum, which suggests that high sorghum yields are possible with good management (Wade et al. 1992). Research in northern India found that ratoon crops produced more fresh fodder and grain than late sown sorghum (Pal and Kaushik 1969), which was attributed to increased tillering. However, the ratoon crop may produce more biomass but less seed production than the original crop (Rao and Damodaram 1972). The cutting height may influence these outcomes, since cutting at 3 cm can lead to infection by disease organisms and higher cuttings at 13 cm can affect the ability of adventitious roots to reach the ground (Escalada 1974). Most research agrees that ratooning sorghum at a high height increases the production of shoots (Rao and Damodaram 1972), achieves more uniform tiller production (Escalada 1974), and obtains the best grain and biomass production (Mackenzie et al. 1970; Escalada 1974; Foloni et al. 2008). However, these experiments compared different cutting heights: 100 cm versus 20 cm (Mackenzie et al. 1970); 22.5 cm versus 10 and 15 cm (Rao and Damodaram 1972); 8 cm versus 3 cm (Escalada 1974); and 36 cm versus 13 cm (Foloni et al. 2008).
Advanced planning may greatly increase the economic success of ratooned sorghum by lowering establishment costs, increasing rainwater efficiency, and reducing soil erosion (Calderwood et al. 1996). Aguiar (1981) argues that the overall yield from three years of annual sorghum ratooning planted in Brazil is technically viable even though grain yields decreased from the original harvest to the two subsequent ratoon croppings. Foale and Carberry (1996) propose that the flexibility of sorghum, including its ratooning ability, makes it a good candidate for on-farm cropping research that aims to reduce farmers’ level of risk. However, cropping systems research involving ratooning sorghum has thus far occurred on research stations. Numerous potential cropping systems that include ratooned sorghum have been identified with positive productivity outcomes (Dunavin 1975; Ramshe et al. 1985; Asokaraja and Ramiah 1988; Brunson and Griffin 1988; Chen and Yein 2005). However, ratooned sorghum was not found to be part of the most productive or economically viable cropping system tested in some cases (Pawar and Thaval 1984; Reddy and Willey 1985; Arunachalam et al. 1993).
The positive effects of applying organic or synthetic fertilizers to ratooned sorghum include reducing days to flowering (Molina et al. 1977), and in one case producing more grain yield than the original crop (Balasubramaniam and Manickasundram 1993). Various other studies have identified the most productive and economical combinations of fertilizers for ratooned sorghum (Touchton and Martin 1981; Lomte and Dabhade 1990; Huang et al. 1992). Some of these studies were conducted in irrigated conditions (Lomte and Dabhade 1990), or in combination with pesticides (Touchton and Martin 1981). However, cropping arrangement may be more critical than fertilization regimes (Bhat and Hosmani 1993).
Very little research has been done to select pigeonpea cultivars for ratoon crops. Gwata and Silim (2009) developed three pigeonpea cultivars for southern and eastern Africa that are compatible with ratooning, however no yield or ratooning comparisons were reported. A high variability in yields from the ratoon crop suggests that more selection is needed for yield stability (Sharma et al. 1978). One possible selection indicator may be high leaf area retention in the original crop, as was observed for short duration pigeonpea varieties in Andhra Pradesh, India (Chauhan et al. 1996).
The ratoon crop of pigeonpea generally produces less than the original crop depending on environmental conditions, but with minimal additional effort. The number of possible harvests, as well as the most productive varieties and planting density, were found to be site specific in India (Chauhan et al. 1984a). For example, reported second harvests from pigeonpea was generally higher for non-ratooned crops than ratooned crops, and the yield potential of the second harvest was greater on Alfisols with one watering than on Vertisols (Venkataratnam and Sheldrake 1985). Even when pigeonpea planted in Vertisol soils suffered attacks from Rhizoctonia bataticola in the dry season, the crops managed to recover in the Monsoon rains, thus producing two subsequent smaller yields, but with minimal additional effort (Chauhan et al. 1984b).
However, there have also been reports that a bushy pigeonpea genotype planted in an Alfisol under semi-arid conditions produced more grain yields in the ratoon crop compared to the original crop regardless of whether or not the crops received micrositing with water or castor cake treatment (Nimbole 1997). Ratooned pigeonpea was found to facilitate cross-pollination between early and medium flowering cultivars (Saxena et al. 1976). Additionally, less flower fall was seen on ratooned early maturing pigeonpea than on non-ratooned crops. Moreover, the differences in grain yield between the main and ratoon crops have been found to differ more when grown on large plots than on small plots (Johansen et al. 1991). Thus, the productivity of ratooned pigeonpea may be largely environmentally dependent.
More investigation is needed on the benefits and drawbacks of different harvesting and ratooning strategies for pigeonpea. In Nigeria, a dwarf pigeonpea variety produced more after two ratoonings when cut at a low height (30 cm) than at a high height (60 cm), however both ratooning heights performed better than crops that were left intact (Tayo 1985). This differs from a study in India that reported the best yields for a short duration pigeonpea were obtained using a full recommended dose of fertilizer and ratooning by plucking the pods rather than cutting (Mahale et al. 1997).
More research is also needed on cropping systems since those involving ratooned pigeonpea were not always found to be the most productive (Yadava and Yadav 1995; Maheshwari et al. 1997). Yadav and Yadav (1991) reported that increasing plant densities decreases yields in the ratoon crop by a third of the orginial harvest. Nevertheless, studies found that cropping systems with ratooned pigeonpea had the highest benefit:cost ratio (Yadav and Yadav 1992, 1995).
Studies on disease and pests of ratooned pigeonpea appear to be much less prevalent than for sorghum. Pandey and Singh (2000) determined that ratooning was unfeasable based on high rainfall years that provoked diseases and excessive plant growth. However, the more resistant genotypes to fusarium wilt have been shown to produce twice as much grain in the second season compared to the first (Reddy and Raju 1997a). In a study from Nigeria, significant seed damage caused by Clavigralla spp. during the reproductive phase of both the original and ratoon crops of pigeonpea was somewhat mediated by intercropping with maize even though overall pigeonpea yields still dropped due the intercropping effect (Dasbak et al. 2012). Moreover, the genotypes of pigeonpea exhibited different pest resistance and grain yields.
Perennial staple crops in Malawi
The scientific literature on ratooning sorghum and pigeonpea clearly shows the limited quantity of research on ratooning sorghum and pigeonpea generally, as well as in southern and eastern Africa. We therefore draw on a wider body of literature to highlight the historic importance of perennial staple crops in Malawi. The history of agricultural policies shows a persistent assumption that soil degradation and human population are the principal causes of food shortages and the determinants of sustainability. The presumption that indigenous practices are not sufficiently productive or effective at protecting soil is complex, and is intertwined with Colonial attitudes toward African farmers and perceived causes of food shortage. We explore some of the history, and consequences for smallholder farming systems in Malawi today.
Food security and land degradation in Malawi is partly a legacy of Colonial policies that discouraged indigenous practices, such as the cultivation of sorghum and pigeonpea. Intercropping is one of the oldest indigenous techniques of crop production in tropical Africa. In Malawi, intercropping increases the chances of obtaining a harvest, improves soil fertility, and maximizes the returns to labor by harvesting multiple crops from the same piece of cleared land (Mulwafu 2011). Indigenous soil conservation strategies – planting outer ridges with trees and grass, planting bananas on contour, and building stone borders – also contribute to sustained yields. These indigenous strategies reduce soil losses, increase soil fertility, and enhance the infiltration and water holding capacities of soils. To this day, stone lines are widely used in steeper areas of Malawi, particularly in remote areas where indigenous knowledge is more prominent (Kanyama-Phiri et al. 2000).
Colonial Era conservation projects transformed interactions between small farmers and the environment. Prior to World War II, governments around the world promoted soil conservation strategies due to concerns that were heightened by the dust storms of the American Dust Bowl. However, in Malawi there was little credence given to indigenous systems of knowledge (Mulwafu 2011). Conservation laws instead required the implementation of techniques that were developed by the Imperial Forestry Institute (IFI) of Oxford, such as contour ridging, box ridging, bunding, and terracing. Not surprisingly, labor-intensive soil conservation laws were unpopular with farmers, and enforcement often involved coercion in the form of penalty fines and physical punishment.
The Colonial Department of Agriculture also prosecuted farmers who cultivated along rivers, who grew polycultures, or who grew hardy perennial sorghum (Vaughan 1987). A vision of modern agriculture was promoted based on the monoculture production of maize (Mulwafu 2011). Sorghum was described by Buchanan (1885) in such terms:
“Sorghum or Kaffir corn is grown chiefly on the river, and in some places in Zomba... Sorghum has the advantage of being biennial: it may even be used for three years, but the third crop is apt to be poor and blanky [sic]. The grain is easier converted to flour than maize: the plant, too, though growing to an immense height -- often 12 feet -- when the soil is good, will yield a fair return in thin shingly soil that would not support maize. The roots of sorghum are of a stronger character, and go farther in search of food.”
In 1949, the Southern Province of Malawi experienced a severe famine when maize crops failed. However, the famine was in fact one hundred years in the making rather than a “subsistence crisis” (Vaughan 1987). Across the Southern Province, there was high variability in the degree of food shortage; wetland maize and drought-resistant crops, like ratooned sorghum, produced well (Vaughan 1987). Fortunately, farmers did not universally adopt the Department of Agriculture’s earlier campaign against the cultivation of such hardy crops, which provided populations with options for local famine relief (Vaughan 1987).
Sorghum and root crops received more attention from the Department of Agriculture following the famine of 1949 because of their contribution to abating hunger. Blantyre produced a surplus of sorghum in the 1950s and Indian traders fostered a cash crop industry for the production of pulses (Vaughan 1987) that likely included pigeonpea. An official sorghum market was established, and farmers increased the production of cassava and the cultivation of wetlands.
Fifty-three years later in 2002, Malawi experienced its next food crisis that once again was not solely due to failures of production. Between 300 and 3000 Malawians are estimated to have died of starvation and diseases related to hunger (Devereux 2002). The national production of maize had fallen by 32 % from a record high of 2.5 million metric tons in the 1999/2000 season to 1.7 metric tons in 2000/2001 due to high rainfall that waterlogged fields. Officials initially explained local maize shortages and increased market prices as the result of Malawian’s “inflexible eating habits” and “strong consumption preference for maize” even though many Malawians relocated to cassava growing areas for food.
Additionally, a decade earlier in 1991/92, a severe drought had reduced maize production in Malawi by less than half of the 2001/02 harvest but with less severe consequences (Eldridge 2002). The 2002 crisis was provoked by the increased vulnerability of poor and rural populations to natural disasters due to declining soil fertility, shrinking landholdings, and increasing rates of HIV/AIDS infection (Devereux 2002). Notably, life expectancy had decreased from 51 to 37 years by 1999, which resulted in severe constraints on adult labor (Haacker 2002).
Moreover, agricultural trade liberalization weakened national institutions, and consequently increased the exposure of Malawians to failures in production, markets, and relief support (Devereux 2002). The Malawian government had compromised its ability to respond to the crisis when it sold its Strategic Grain Reserve (SGR) to Kenya and Mozambique between April – May 2001. The International Monetary Fund (IMF) had encouraged Malawi to sell part of its SGR to pay for its debts. Malawi had harvested bumper maize yields in the two previous seasons that could have very well averted the crisis.