Effect of different fertilizer amendments on the growth and yield of groundnut and Cercospora leaf spot disease incidence

Early leaf spot (ELS) and late leaf spot (LLS) diseases of groundnut ( Arachis hypogaea) caused by Cercospora arachidicola Hori and Cercosporidium personatum, respectively are economically important foliar diseases in Ghana and can cause considerable yield losses of 50-70% in groundnut in West Africa through reduction of photosynthetic leaf surface and stimulation of leaflet abscission resulting in extensive defoliation. Leaf spots are the most common and serious diseases of groundnut in northern Ghana. In Ghana, pod yields of groundnut crops remain low below 1.0 t ha-1, which is far less than the potential yield of 2.0-3.0 t ha -1 thereby affecting groundnut production, the income and welfare of groundnut growers. It is, however, not clear whether the problem of low yields in groundnut, especially in northern Ghana, is as a result of declining soil fertility or Cercospora leaf spot disease infection or changes in climatic conditions. This study examined the effects of application of nutrient amendments on the growth, grain yield and Cercospora leaf spot resistance of Chinese, the most commonly grown groundnut variety in northern Ghana. The trials were conducted on-station at Nyankpala in the Guinea Savanna zone of Ghana. The Chinese was planted at 60 cm x 20 cm at two plants per hill. Treatment combinations used were SSP, TSP (30 kg P/ha), organic manure (4 t/ha)+TSP and organic manure+TSP+BoostXtra and a control treatment with no input. SSP and TSP were side-dressed and the organic manure (FertiSoil) incorporated into the soil one week before planting. The BoostXtra (a compound micronutrient formulation) was foliar-sprayed at two weeks interval beginning from 50% flowering till maturity. Both ELS and LLS disease severities and per cent defoliation were assessed using the ICRISAT Scale. The combination of TSP and manure greatly enhanced haulm, shell and biomass dry weights and grain yield. The increased grain yield can generally be attributed to increased seed size. Except seed size, these parameters were also increased when the TSP+Manure treatment received BoostXtra producing a grain yield increase of 64%. Nutrient amendments significantly increased the resistance of Chinese to leaf spot disease which subsequently reduced defoliation. Susceptibility of Chinese to leaf spot disease, resulting in low grain yields, can therefore increase in soils with low fertility but this can be averted by applying nutrient amendments to the crop.