Gaseous emissions from soil biodisinfestation by animal manure on a greenhouse pepper crop

Abstract

Soil solarisation together with the application of animal manure has been described as an alternative process for control of Phytophthora capsici root rot in pepper crops. A mixture of fresh sheep manure and dry chicken litter (SCM) and a semi-composted mixture of horse manure and chicken litter (HCM) were applied at 5.1 kg m −2 (dry weight) under plastic sheets to reduce Phytophthora inoculum survival rate and disease incidence. Non-solarised (C) and solarised (S) soils were used as control treatments. Mean NH 3 concentration increased in SCM during biodisinfestation process (14.8 mg NH 3 m −3) compared with HCM (9.1 mg NH 3 m −3), accounted for the higher organic N content and potential N mineralisation. The higher NH 3 concentration in SCM could have contributed to reduce the inoculum survival rate (30.6% and 75.0% in SCM and HCM plots, respectively). Inoculum survival rate was not reduced in S (94.4%) as temperature was below 33 °C throughout the experimental period. After biodisinfestation treatment, N 2O and CO 2 emissions tended to be higher in SCM, despite high spatial variability. Cumulative N 2O emissions were 1.31 and 0.42 g N 2O-N m −2 in SCM and HCM after 43 days. The larger N application and organic N mineralisation rate on fresh manure amended soils might have contributed to higher N 2O emissions during and after soil biodisinfestation by denitrification and nitrification, respectively. Cumulative CO 2 emission averaged 211.0 and 159.9 g CO 2-C m −2 in SCM and HCM, respectively. The soluble organic C, more abundant in fresh manure, might have favoured soil respiration in SCM. Disease incidence decreased in SCM and HCM plots (disease incidence, 2%–8%) in relation to solarised soils (42%) after 4 months. Microbial suppressiveness might have contributed to minimise Phytophthora disease incidence in SCM and HCM plots. Pepper fruit yield increased with manure amendment in SCM and HCM, which averaged 4.6 and 4.3 kg m −2, respectively. Further research will be necessary to guarantee an effective Phytophthora biodisinfestation by fitting manure N and organic matter applications, improving crop yield and reducing greenhouse gas pollution.