Soil nitrogen dynamics and sorghum productivity as affected by biochar in the dry tropics

Biochar combined with other applications has gained attention to improve crop productivity, however, the effect of biochar application on soil nitrogen (N) dynamics and sorghum productivity in dry tropics remains underexplored. A field experiment was conducted on sorghum cultivation in the cropland of south India to evaluate the effect of biochar (15 Mg ha(-1)) and biochar combined with chemical fertilizer (CF) or farmyard manure (FYM) application (100 kg N ha(-1) yr(--1)) on soil N dynamics (inorganic N and microbial biomass N [MBN]), soil moisture, and crop productivity (grain yield, total N uptake, and nitrogen use efficiency [NUE]). Biochar sole application improved the soil moisture condition for approximately 3 years, though did not increase soil N dynamics and crop productivity. Grain yield and total N uptake in biochar with CF treatment were larger than that in control in the rainy years but were not different from that in the CF treatment. CF application increased the soil inorganic N until the flowering stage but did not affect MBN. FYM application increased MBN and inorganic N only during the early growth stage, resulting in no clear improvement in crop productivity. Considering the highest NUE for 3 years in biochar with CF treatment, our results indicate that both improved soil water condition by biochar application and better inorganic N availability until the flowering stage through N application would be required to improve crop productivity and consequently, NUE, in the nutrient-poor soils of south India.

Automated summary

The study found that using biochar in croplands in South India can improve soil moisture, and combining it with chemical fertilizer can increase crop productivity, especially during the rainy season. However, using biochar alone does not increase soil nitrogen dynamics and crop productivity.