Upland Cotton (Gossypium hirsutum L.) is an essential economic commodity for millions of more than 200,000 small-scale of Zambian cotton farmers. The cotton production plays an important role in the economy of both agricultural and industrial sectors. Despite this importance of cotton production in Zambia,it is characterized by low productivity due to biotic and abiotic stresses coupled with poor agricultural practices. However, abiotic stress like; soil acidity, high temperature, low inherent soil fertility and drought stress are the main factors restricting cotton production and sustainable agricultural development in south east Africa. Cotton is the main fibre crop in Zambia that earns over 40 million dollars in forex earnings. Cotton has low yields in Zambia ranged from 300kg to 600kg per hectare when the actual potential of the varieties in the country is above 2500kg per hectare (ICAC, 2023). One of the major factors affecting low yield is abiotic stress and the lack of proper fertile soils. Soil fertility can be enhanced by the use of both organic and inorganic fertilizers. Zambian farmers did not apply fertilizers due to its high price for smallholder farmers. The implication of this finding is crucial considering that approximately 30% of the world's soils are acidic, including more than 50% of potential arable land. Shitumbanuma et al., 2015 reported that most of the soils in Zambia are acidic, that makes most of the essential nutrients unavailable for the cotton plant. So, the cheep solution for the Zambian farmers is using organic manures and Biochar fertilizers.
The Zambian agricultural policy is focusing on improving soil fertility for the sustainability and increased production systems approach. This improvement requires the integration of sustainable land management (SLM) measures and added organic matter to the soil will lead to increasing carbon stock whose depletion leads to soil degradation. Recently, many studies have explained the sustainable management of soil fertility. These techniques involves use of different types of organic matter like; compost, manure crop residues, green manure, fertilizer micro-dosing, etc. which, led to the improvement of physical, chemical and biological properties of the soil. Also, the benefits to cotton nutrient content, growth, yields, productivity, and economic benefits (Tovihoudji et al. 2022 and Li et al., 2023).
Biochar, “green charcoal”, is a result of the slow pyrolysis of plant biomass (straw) in a under hypoxia or anaerobic conditions at 300–1000 ℃, which produces a product with very high carbon content. Biochar is an economical and efficient soil conditioner to improve the pH and bioavailability of soil nutrients, when mixed with organic or mineral fertilizer (Rutigliano et al., 2014). Soil pH between 5.4 and 6.9 were shown to be the best for cotton production (Sharry, 2019). Generally, applying Biochar to not very fertile, moderate fertile or degraded soils has a positive effect on improving soil environment and enhances crop yields rather than healthy fertile soil (Akhtar et al., 2014).
Addition of Biochar to low fertility soils has positive effects on agricultural systems. Firstly, benefits of Biochar on soil physical properties are; it enhances water holding capacity, decreases bulk density, increases soil porosity in the no mulching zones, saturated soil water content, field capacity, planar soil water storage, and improves water retention and crop growth (Liang et al., 2021). Secondly, it enhances chemical soil properties; increases nutrient content, increases soil organic carbon (Xiao et al., 2016), enhances nutrient components such as soil mineral N content (ammonium, nitrate and total nitrogen) and dissolved organic carbon. 4.0 t / ha of Biochar application dose (BCAR) has significantly improved soil physical-chemical properties of cotton fields (Karthik et al., 2019). Thirdly, decreasing the difference between day and night soil temperatures by 0.66 to 1.39◦C, (Liu et al., 2018) and mitigated some of the “pulse” effects of rainfall on emissions (Maucieri et al., 2017). Fourthly, biochar improves soil quality and significantly increases root growth and crop production by 10%. Hossain et al., 2020 found that addition of Biochar increases the availability of potassium by slowing down the process of leaching from the soil, and increases nitrogen retention by reducing leaching and gas emissions.
On the other hand, Biochar is not a fertilizer and application of too much Biochar can injure plants, possibly by increasing soil alkalinity. Also, rich soils in organic matter can temporarily reduce nitrogen levels because microbes will out-compete plants in sequestering this nutrient. Many studies have shown that too much Biochar is harmful to plants and soil. You can't correct this problem without removing the soil and may be more beneficial for acidic soil where the increase in pH is desirable rather than alkaline soils which have high pH. Li et al., 2023 reported that the Biochar application rate/amount/dose is a very important parameter, due to its effect on crop growth, yields and productions to a high extent.
All methods for Biochar production required the use of wood chippers. However, large chunks of Biochar should be crushed before adding to soil. The physi-cochemical properties of test Biochar were found as, pH = 8.78, organic carbon (OC) = 281.33 g kg− 1, total nitrogen (TN) = 7.49 g kg− 1, ammonium (AN) = 1.59 mg kg− 1, nitrate (NN) = 24.33 mg kg− 1, available phosphorus (AP) = 1.38 mg kg− 1, available potassium (AK) = 4.62 g kg− 1. Due to the high properties of Biochar,it is increasingly being used as a fertilizer for different crops (Ahmad et al., 2014). Biochar addition retains a higher N concentration in the soil; ensuring plants have less trouble with nutrient absorbing. In fact, a 2020 study found that Biochar fertilizers improved plant nitrogen absorption by 12% more than urea (the popular nitrogen fertilizer). A few ways to apply Biochar are top-dressing, tilling or hand mixing. Top dressing - simply sprinkles your charged biochar on top of the soil and wet it, is the most effective method. The amendment of Biochar significantly increased the pH of acidic soils (yellow-brown soil and fluvo-aquic soil) by 0.5 -1. However, the pH of the black soil was significantly decreased by 0.5 units. Biochar doesn't decompose. In acid soils, liming effect of Biochar enhances soil microbial diversity and its function, together with increasing caution exchange capacity and crop water availability.
The objectives of the study is to test cotton stalks Biochar doses mixed with different fertilizer types over two growing seasons for impacts growth, cotton yield productivity and determine the most economical biochar application dose and type (BCAR) for commercial cotton variety CDT V in Magoye region of Zambia.