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Orphan crops are indigenous and invariably grown by small and marginal farmers under subsistence farming systems. These crops, which are common and widely accepted by local farmers, are highly rich in nutritional profile, good for medicinal purposes, and well adapted to suboptimal growing conditions. However, these crops have suffered neglect and abandonment from the scientific community because of very low or no investments in research and genetic improvement. A plausible reason for this is that these crops are not traded internationally at a rate comparable to that of the major food crops such as wheat, rice, and maize. Furthermore, marginal environments have poor soils and are characterized by extreme weather conditions such as heat, erratic rainfall, water deficit, and soil and water salinity, among others. With more frequent extreme climatic events and continued land degradation, orphan crops are beginning to receive renewed attention as alternative crops for dietary diversification in marginal environments and, by extension, across the globe. Increased awareness of good health is also a major contributor to the revived attention accorded to orphan crops. Thus, the introduction, evaluation, and adaptation of outstanding varieties of orphan crops for dietary diversification will contribute not only to sustained food production but also to improved nutrition in marginal environments. In this review article, the concept of orphan crops vis-à-vis marginality and food and nutritional security is defined for a few orphan crops. We also examined recent advances in research involving orphan crops and the potential of these crops for dietary diversification within the context of harsh marginal environments. Recent advances in genomics coupled with molecular breeding will play a pivotal role in improving the genetic potential of orphan crops and help in developing sustainable food systems. We concluded by presenting a potential roadmap to future research engagement and a policy framework with recommendations aimed at facilitating and enhancing the adoption and sustainable production of orphan crops under agriculturally marginal conditions.

Abstract:Fertilizer application is known to increase crop yields and mitigate net soil nutrient mining due to continuous removal. However, smallholder farmers rarely apply adequate fertilizers because of high cost, limited availability and lack of awareness. An experiment was conducted to evaluate the effect of chicken manure on cassava root and biomass yield at Kabangwe and Mansa, two locations representing agroecological zones II and III, respectively, in Zambia. With the aim of exploring alternative soil fertility management for smallholder farmers, the effect of sole chicken manure and mineral fertilizers was evaluated on cassava. The treatments were four levels of chicken manure (0, 1.4, 2.8, 4.2 ton/ha) and a single level of mineral NPK applied at 100N-22P-83K kg/ha as recommended. The design was a Randomized Complete Block (RCBD), with three replications using the improved cassava variety "Mweru" during the 2015/2016 growing season. The results showed significant (p < 0.05) treatment effects on cassava root yields and yield components (fresh and dry root, leaf, stem, and total biomass) at both sites. The highest mean fresh (27.66 ton/ha) and dry root yield (9.55 ton/ha), and total fresh biomass (53.68 ton/ha) and dry biomass (16.12 ton/ha) production were achieved with the application of 4.2 ton/ha of chicken manure. This treatment showed 71% and 81% fresh root yield advantage over the control at Mansa and Kabangwe, respectively. While the marginal rate of return (MRR) was negative for the mineral fertilizer, it was positive for all the chicken manure treatments with the maximum (315%) achieved from the application of 4.2 ton/ha. The study concludes that application of chicken manure significantly increases the yield and biomass production of cassava and is economically efficient.

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