Plant Enzymes, Root Exudates, Cluster Roots and Mycorrhizal Symbiosis are the Drivers of P Nutrition in Native Legumes Growing in P Deficient Soil of the Cape Fynbos in South Africa

The Cape fynbos is characterised by highly leached, sandy, acidic soils with very low nutrient concentrations. Plant-available P levels range from 0.4 μg P g-1 to 3.7 μg P g-I soil, and 1-2 mg N gl soil. Despite these low nutrient concentrations, the fynbos is home to 9,030 vascular plant species with 68.7% endemicity. How native plant species survive such low levels of available P is intriguing, and indeed the subject of this review. In the fynbos soils, P is easily precipitated with cations such as Fe and Al, forming AI-P and Fe-P in acidic soils, or Ca-P in neutral-to-alkaline soils. The mechanisms for promoting P availability and enhancing P nutrition include the development of mycorrhizal symbiosis （with 80%-90% of higher plants, e.g., Cyclopia, Aspalathus, Psoralea and Leucadendron etc.） which exhibits 3-5 times much greater P acquisition than non-mycorrhizal roots. Formation of cluster roots by the Leguminosae （Fabaceae） and their exudation of Kreb cycle intermediates （organic acids） for solubilizing P, secretion of root exudate compounds （organic acids, phenolics, amino acids, etc.） that mobilize P. The synthesis and release of acid and alkaline phosphatase enzyme that catalyze the cleavage of mineral P from organic phosphate esters in acidic and alkaline soils, and the development of deep tap roots as well as massive secondary roots within the uppermost 15 cm of soil for capturing water and nutrients. Some fynbos legumes employ all these adaptive mechanisms for enhancing P nutrition and plant growth. Aspalathus and Cyclopia species typically form mycorrhizal and rhizobial symbiosis for improving P and N nutrition, produce cluster roots and acid phosphatases for increasing P supply, and release root exudates that enhance P solubilisation and uptake.

Science and Technology Backyard model:implications for sustainable agriculture in Africa

Sustainable food production to feed the growing population in Africa remains a major challenge.Africa has 64%of the global arable land but produces less than 10%of its food locally due to its inherently low soil nutrient concentrations.Poor soil fertility and a lack of fertilizer use are the major constraints to increasing crop yields in Africa.On average only about 8.8 kg NPK fertilizer is applied per hectare by African smallholder farmers.There is therefore considerable potential for increasing food production through sustainable intensification of the cropping systems.The low crop yields in Africa are also partly due to limited farmer access to modern agronomic techniques,including improved crop varieties,a lack of financial resources,and the absence of mechanisms for dissemination of information to smallholders.This study analyzed the Science and Technology Backyards(STBs)model and investigated its use for the transformation of agriculture in Africa.Some key lessons for sustainable crop intensification in Africa can be found from analysis of the STB model which is well established in China.These include(1)scientist-farmer engagement to develop adaptive and innovative technology for sustainable crop production,(2)dissemination of technology by empowering smallholders,especially leading farmers,and(3)the development of an open platform for multiple resource involvement rather than relying on a single mechanism.This review evaluates the benefits of the STB model used in China for adoption to increase agricultural productivity in Africa,with a perspective on sustainable crop intensification on the continent.