Standard protocol for a biochar field trial
Selection of the test area
Repartition of the plots
Amendment of the plots
1. Selection of the test area
A test area is composed of 30 square plots of side 4 meters each, separated by a 1 meter-wide space. It is very important that the soil composition be as uniform as possible, so the 30 plots should be contiguous and the soil of the test area should have received everywhere the same treatments (crops, amendments, irrigation…) in the past and should not contain any irregularity (creek, underground spring, soil accumulation…).
2. Repartition of the plots
Only 10 different amendments (A1, A2, B1, B2, C1, C2, D1, D2, E1, E2) will be tested, each one repeated on 3 different plots in order to further reduce the potential influence of external parameters on the results. The 3 plots with the same amendment should furthermore be located as far as possible from each other, for instance according to the following pattern:
3. Amendment of the plots
Two types of biochar (types 1 and 2) and five types of complementary fertilization (amendments A, B, C, D and E) will be tested according to the following posology:
The required quantities of biochar and fertilizer will be weighted, mixed and spread on the corresponding plots in a layer that should be as uniform as possible. The type “Control” corresponds to the soil without any amendment (baseline situation). This layer can then be incorporated uniformly in the soil by tillage (up to a depth of 18-20 cm), either manually or with a rotocultivator if available. It is very important to handle all plots the same way, so the control plots have to be tilled as well!
A locally available crop should be preferred, which shows only a reduced sensitivity to parasites or illness (usually onions, rice, okra may be good choices). The chosen crop should be planted following the same repartition on all the plots and, again, any further treatment (soil amendment or irrigation, foliar fertilization, pesticide…) should be systematically applied in a similar manner on all the plots of the test area.