Farmer‐led maize biochar trials: Effect on crop yield and soil nutrients under conservation farming

Abstract

In extensive farmer‐led trials practicing conservation farming (CF) in three regions of Zambia (Mongu: sandy soils; Kaoma: sandy or loamy sand soils; Mkushi: sandy loam or loamy soils), we studied the effects of biochar made of maize cobs (0, 2, and 6 t ha−1 corresponding to 0, 0.8, and 2.5% per basin) at different fertilizer rates of NPK and urea on crop yield of maize (Zea mays) and groundnuts (Arachis hypogaea). Conservation farming in this case combines minimum tillage (how basins), crop rotation and residue retention. For the first time, the effect of biochar on in situ soil nutrient supply rates [determined by buried Plant Root Simulator (PRS™) exchange resins] was studied, as well as the effects of biochar on elemental composition of maize. Effects of 0–10% (w:w) biochar addition on soil physical and soil chemical properties were determined in the laboratory. At all sites there was a consistent positive response in crop yield upon the addition of biochar. However, due to a great variability between farms there were no significant differences in absolute yields between the treatments. In the sandy soils at Mongu, relative yields (i.e., percentage yield with biochar relative to the same fertilizer rate without biochar) of maize grains and maize stover were significantly increased at recommended fertilizer rates (232 ± 60%) and at half the recommended rate (128 ± 6%), respectively. In addition, biochar significantly increased concentrations of K and P in maize stover. In situ soil nutrient supply rates as measured by PRS™‐probes were highly spatially variable with no consistent effects of the different treatments in the three regions. By contrast, the fraction of plant available water (Vol.‐%) significantly increased upon the addition of biochar in all three soils. The increase caused by 10% biochar addition was of factor 2.5 in Mongu (from 4.5% to 11.2%) and 1.2 in both Kaoma (from 14.7% to 18.2%) and Mkushi (from 18.2% to 22.7%). Cation exchange capacity, pH, and exchangeable K significantly increased upon the addition of 10% (w:w) biochar in all three regions with a subsequent increase in base saturation and decrease of available Al3+. Our findings suggest that the addition of biochar in combination with CF might have a positive impact on crop growth and that this positive effect is mainly caused by increases in plant‐available water and decreased available Al.

Biochar amendment increases maize root surface areas and branching: a shovelomics study in Zambia

“…The proliferation of primary and secondary lateral roots is a well-348 observed answer of plants to higher availability of nutrients in a specific zone of the soil 349 (Hodge, 2004). This specific development of roots is particularly observable for immobile 350 nutrients like phosphorus (Lynch, 2011) With regard to chemical effects, biochar has been observed to result in higher K contents in 363 both the soil solution (from around 150 to around 300 µg cm sampler -2 month -1 in plant root 364 simulator ion exchange membranes) and in plant tissue (from around 5000 to 8000 mg kg -1 ) at 365 these two sites in Zambia (Martinsen et al, 2014). Also P availability can be expected to 366 increase with the pH increase brought about by the biochar (Kaoma, pH from 4.6 to 6.3, 367…”

“…We hypothesised a 128 modification of the root architecture upon biochar addition with greater effects of biochar in 129 the sandy soils of Kaoma (based on observations of greater yield effects were observed in 130 earlier studies (Cornelissen et al, 2013;Martinsen et al, 2014)) as compared to the loamy 131 soils at Mkushi. This work will help in understanding why biochar can have positive effects 132 on crop yield, and thus at which sites these beneficial effects can be expected.…”

“…This observation was corroborated by the root system size increases 321 that were significant for some of the sites, such as those in the root area (+54±14%; n=32;p<0.005) and related parameters such as root depth (+10±7%; n=32; p<0.05), root angle 323 opening (+14±11%; n=32; p<0.01) and fine root development expressed by the number of 324 holes in the images (+70±56%; n=32; p<0.01). Again, both the changes in root architecture 325 and grain yield are caused by BC, but the larger yields are not necessarily caused by the root 326 system changes -both are expressions of the fact that biochar causes significant changes in 327 soil biology, chemistry and physics (Martinsen et when there was an increase in relative yields of 178% and 289% (p>0.05) at 2 and 6 t biochar 338 per ha, respectively in Kaoma and 109% and 110% at 2 and 6 t biochar per ha, respectively in 339 Mkushi (p>0.05) (Martinsen et al 2014). This corroborates previous findings indicating that 340 biochar has generally a more positive effect in soils with low fertility (Crane-Droesch et al, 341…”

Biochar Application in Malaysian Sandy and Acid Sulfate Soils: Soil Amelioration Effects and Improved Crop Production over Two Cropping Seasons

“…Laird et al [31] reported that the addition of biochar to weathered soils (fine loamy, typic hapludolls) can increase exchangeable potassium via both the addition of potassium that is contained in the ash fraction of the biochar, and by binding potassium and thus reducing losses through leaching. Martinsen et al [32] observed significantly higher K contents in both the soil solution and maize plant tissue after the amendment of biochar, corresponding to the amounts of K added via the biochar (68 kg/ha) amendment rather than via the addition of fertilizer (28 kg/ha). Masulili 2010, [33] reported that the addition of 10 t/ha rice husk biochar to acid sulfate soil cropped with rice increases exchangeable calcium significantly compared to a control.…”

Action Research into a Flood Resilient Value Chain – Biochar-Based Organic Fertilizer Doubles Productivity of Pea in Udayapur, Nepal

“…There is a potential to increase income by harnessing urban city markets [18]. The key challenges to realizing the potential of peas to contribute to farm income include the lack of storage for longer periods post harvest due to the need for immediate cash to meet regular needs; poor information about markets; lack of structured markets;…”