Richard Lambert

Evaluation of the long-term effect of biochar on properties of temperate agricultural soil at pre-industrial charcoal kiln sites in Wallonia, Belgium

Research on biochar has increased, but its long-term effect on the fertility of temperate agricultural soil remains unclear. In Wallonia, Belgium, pre-industrial charcoal production affected former forested areas that were cleared for cultivation in the nineteenth century. The sites of traditional charcoal kilns, largely enriched in charcoal residues, are similar to soil amended with hardwood biochar more than 150u2009years ago. We sampled 17 charcoal kiln sites to characterize their effect on soil properties compared with adjacent reference soils. Charcoal-C content was estimated by differential scanning calorimetry. The kiln soil contains from 1.8 to 33.1u2009gu2009kg−1 of charcoal-C, which markedly increases organic C:N and C:P ratios. It also contains slightly more uncharred soil organic carbon (SOC) than the reference soil, which accords with larger total N content. We measured a small increase in nitrates in the kiln soil that might relate to greater mineralization and nitrification of organic N. Frequent application of lime raised the pH to values close to neutral, which offset the residual effect of charcoal production on soil acidity. A cation exchange capacity (CEC) of 414u2009cmolcu2009kg−1 was estimated for charcoal-C, whereas that of uncharred SOC was 213u2009cmolcu2009kg−1. Despite the large CEC of the kiln soil, exchangeable K+ content was no different from the adjacent soil, whereas exchangeable Ca2+ and Mg2+ contents were considerably larger. Charcoal enrichment has little effect on available, inorganic and total P, but it can form strong complexes with Cu, which reduces the availability of the metal. Biochar is very persistent in soil; therefore, long-term implications should not be overlooked. n nHighlights nCharcoal kiln soil contains from 1.8 to 33.1u2009gu2009kg−1 of charcoal-C, which raises C:N and C:P ratios. nCharcoal-C content was estimated by differential scanning calorimetry. nWe estimated a CEC of 414u2009cmolcu2009kg−1 for charcoal-C and 213u2009cmolcu2009kg−1 for uncharred SOC. nRetention of exchangeable K+ remained unaffected by charcoal but that of Ca2+ and Mg2+ increased.

LAI evolution of a perennial ryegrass crop estimated from the sum of temperatures in spring time

When there is sufficient fertiliser, the development of the canopy (LAI less than or equal to 4) of a perennial ryegrass crop during regrowth after winter or after a cut in spring time, essentially depends on the temperature. The expression of the Leaf Area Index (LAI) according to the sum of average positive temperatures instead of relatively to the number of days highly improves the relationship. This is verified at three sites, where climatic conditions are different, during 2 consecutive years and is written L = 0.0193 Sigma T-0.3107 (Tin degrees C). On average, 52 degrees C/day are required to allow a LAI increase of 1 unit in spring time. The LAI expansion results from the increase of the number of tillers, of leaves per tiller and of the leaf area. The relationship between the sum of temperatures and each of these factors is not significant, except for the tiller density. Adversely, the result obtained by the product of these factors, the LAI, is significantly correlated to the sum of average positive temperatures calculated from the beginning of the growth after winter

Sustainable Nitrogen Management in Agriculture

In order to reduce the pollution caused by nitrates from agricultural sources, the Walloon region has established a Programme of Sustainable Nitrogen Management in Agriculture. This legislation encompasses all compulsory measures mentioned in the European Directive known as ‘Nitrate Directive’ (Directive 91/676/EEC), but its scope is larger, as it defines obligations regarding storage and management of livestock manure outside vulnerable zones. The Walloon legislation is the result of a long negotiation process and represents a common understanding between the Public powers, the farmer’s unions and the water producers, purifiers and distributors. It was launched in October, 2002. Three complementary levels are concerned: the field, the whole farm and the region. At field level, the objective is to reduce nitrate losses through leaching during winter. The farmer must put in place some good agriculture practices, particularly regarding authorised doses and periods of application of nitrogen fertilisers. At the whole farm level the farmer must maintain a balance between the organic nitrogen compound to be applied and his land application capacity (i.e.: the applicable quantity legally authorised). Every year, the soil link rate (LS) of each farm is calculated by the government administration, taking into account several factors: the number of animals on the farm, average values of nitrogen production per animal category, agricultural land surface available and authorised doses of nitrogen organic compound applicable. In vulnerable zones, organic nitrogen application is limited to 80 kg N/ha on arable land and 210 kg N/ha on grassland. Outside these vulnerable zones, the amount of livestock manure applied is limited to 120 kg N/ha on arable land and 210 kg N/ha on grassland. The organic nitrogen in excess of the land application capacity must be transferred to other farms that are able to value it.