Fertilizer tree

The use of Faidherbia albida in Malawi and Zambia has resulted in a doubling or even tripling of maize yields.[7] As part of evergreen agriculture, use of fertilizer trees is proposed as a means to improve food security. Niger has more than 4.8 million hectares of predominantly Faidherbia agroforests, while Zambia has 300,000 hectares.[7] In Zambia and Malawi, farmers plant the trees in a checkerboard pattern every 30 feet.[8]

Fertilizer trees are used to prevent the expansion of desert, and to keep agriculture viable in arid lands in many African countries.[9]

1. Increased Crop Productivity: By means of biomass transfer, fertilizer trees can be harnessed to boost vegetable yields. Biomass transfer involves relocating tree biomass, like pruned branches, generated in one section of the farm (e.g., in protein banks or fallow areas) to another part (e.g., a vegetable garden).[10] This practice has shown to enhance the productivity of cash crops in association with fertilizer trees.[10] For instance, the presence of shade trees alleviates stress on crops like coffee and cacao by mitigating unfavorable climatic conditions and nutritional disparities.[11] This, in turn, leads to an overall increase in system productivity within multistrata agroforestry setups.[11]
2. Improvement in soil nutrient cycling: Fertilizer trees possess the potential to furnish adequate quantities of nitrogen (N) to sustain moderate crop yields by (1) contributing N through biological nitrogen fixation and the recovery of nitrate from deeper soil strata and (2) facilitating the recycling of N from plant residues and organic fertilizers.[12] Nevertheless, it's important to note that fertilizer trees are unable to generate new supplies of various nutrients.[13] However, they can enhance the accessibility and absorption of these nutrients by crop plants through diverse mechanisms. In the case of phosphorus (P), the recycling from organic materials usually falls short of fulfilling the P demands of crops.[13]
3. Soil Rehabilitation Services: To comprehend the mechanisms behind the aforementioned yield enhancements, it's essential to investigate how the introduction of fertilizer trees to the agricultural environment contributes to the restoration of soil fertility and the stimulation of biological processes and ecological functions.[10] These are the fundamental processes that offer substantial advantages to individual farmers and society at large.[10] Among these crucial services are nutrient cycling, elevated accessibility of macronutrients (such as extractable N, P, and K), cations, and soil pH improvement, augmented organic matter content (SOM), heightened biological activity, enhanced soil physical characteristics, and improved water relationships.[10]
4. Increased soil organic matter: Fertilizer trees contribute to the augmentation of soil organic matter (SOM) in two ways: by generating SOM and by mitigating losses attributed to erosion.[10] The heightened presence of soil organic carbon (SOC), especially in the lighter fraction, is recognized for its capacity to enhance aggregate stability, porosity, hydraulic conductivity, and soil structures that are resilient against erosion.[10]
5. Decrease soil insect pests and weed: In specific agroforestry practices, the inclusion of fertilizer trees has been found to have the potential to decrease soil insect pests and weed-related issues.[14] For instance, enhanced fallows incorporating fertilizer trees in Zambia led to a reduction in termite damage to maize.[15] Of particular importance is the effective control of troublesome weeds like spear grass (Imperata cylindrical).[10] Fertilizer tree fallow systems have demonstrated effectiveness in mitigating the issue of parasitic witch weeds (Striga spp.), a problem commonly linked to low soil fertility in Africa.[14]
6. Improvement in soil biological properties: The evaluation of how fertilizer trees affect soil biological properties can be conducted by observing alterations in the abundance, diversity, and structure of soil organisms and plant life, microbial biomass, enzyme activity (e.g., respiration), as well as soil pests and weeds.[10] Soil organisms, in particular, play a pivotal role in the decomposition of litter, influencing interactions among plants and soil microbial communities.[10] Throughout the decomposition process, organic nutrients within the litter are transformed into inorganic forms, which can then be absorbed by growing plants.[10] Additionally, the actions of soil organisms enhance both soil water infiltration and retention, factors of growing significance in promoting agricultural sustainability within arid climates.[16] Fertilizer tree species have demonstrated the ability to swiftly rehabilitate soil fauna, even in severely degraded soils.[16]
7. Improvement in soil physical properties: Commonly used indicators for assessing soil physical properties encompass measurements such as soil depth, bulk density, aggregate stability, infiltration rates, water-holding capacity, and penetration resistance.[10] Soil bulk density serves as a direct gauge of soil compaction. Soils with low bulk density, even if they have an open texture and porosity, are susceptible to issues such as erosion, poor water retention, as well as the oxidation and loss of soil organic matter and soil organic carbon.[10] In contrast, soils with high bulk density exhibit reduced porosity.[10] Numerous studies have shown that the presence of fertilizer trees leads to improvements in bulk density, aggregate stability, and porosity.[10] In sandy loam soil within the pre-Amazon region of Brazil, a three-year period of alley cropping with tree species like leucaena, pigeon pea, acacia, and their mixtures resulted in significant enhancements in bulk density, total porosity, and soil aeration.[17]
8. Carbon Sequestration and Greenhouse Gas Mitigation Potential: Fertilizer trees possess the capacity to sequester substantial amounts of carbon (C), both within the soil and in their woody biomass, thereby mitigating greenhouse gas (GHG) emissions.[10] This aspect can play a pivotal role in climate change mitigation as it promotes nutrient recycling and carbon sequestration in croplands and pastures.[10] Nevertheless, the potential for accumulating ecosystem carbon through the utilization of fertilizer trees is contingent upon site-specific characteristics and planting densities.[10] Consequently, the application of precise methods is essential for assessing changes in carbon content resulting from the incorporation of fertilizer tree innovations into various agricultural systems.[10]
9. Provision of Products: The majority of nitrogen-fixing trees offer a range of products, such as timber, fruits, edible seeds, and protein-rich fodder, which contribute to the enhancement of pasture productivity.[10] Other products include:
   • Wood and Wood Products: Significant quantities of firewood and timber are produced from the cultivation of fertilizer trees on agricultural land.[10] This abundant wood production underscores the potential of these trees in fulfilling the local demand for firewood, particularly in Africa, where the population relies heavily on forest wood extraction due to the scarcity of alternative energy sources.[10] As forest resources continue to deteriorate, the availability of firewood diminishes, and rural women are forced to travel longer distances in search of firewood.[10] By planting fertilizer trees on farmland, access to firewood for women can be improved, allowing them to redirect the time and effort spent on gathering firewood towards activities like food production and childcare.[10]
   • Fruits and Edible Seeds: Certain fertilizer trees, including tamarind, parkia, pigeon pea, Tetrapleura tetraptera, among others, yield edible seeds or kernels.[10] For instance, pigeon pea seeds are nutritionally rich, providing protein, carbohydrates, minerals, and vitamins, making them an ideal complement to the predominantly starch-based diets commonly found in Africa and Asia, which are typically lacking in protein.[18] The edible pulp of tamarind is either consumed fresh or utilized to prepare syrup, juice concentrates, and a variety of exotic culinary delights such as chutney, curries, pickles, and meat sauces.[10]
   • Fodder and Pasture: In semi-arid regions, livestock productivity faces significant challenges due to a shortage of forage and limited access to high-quality feed.[10] Silvopastoral management strategies, which encompass the establishment of protein (fodder) banks and grazing systems involving fertilizer trees, can offer partial solutions to these issues.[10] Protein banks enable animals to be provided with stall-fed fodder obtained from trees such as gliricidia, calliandra, leucaena, pterocarpus, and other species, which are cultivated in designated blocks on farmland.[10] Alternatively, grazing systems permit livestock to graze on pastures situated under widely spaced trees (e.g., alley farming) or dispersed trees (e.g., parklands).[10]

• Agroforestry
• Ecoscaping
• Green manure, fertilization with herbaceous legumes