In a natural ecosystem, energy from producers flows into many food chains. On a farm, any energy that goes to organisms other than the crop or livestock, such as weeds, insect pests or fungi, is lost to the human food chain. Simplifying the food web redirects that energy to humans.Methods include:• Herbicides kill weeds. Weeds compete with crop plants for light, water, mineral ions and space, so removing them lets the crop convert more light energy into its own biomass.
• Insecticides kill insect pests that eat the crop, so less of the crop's biomass (and energy) passes to non-human food chains.
• Fungicides kill fungi that cause crop diseases.
• Biological control uses a natural predator or parasite to reduce a pest population, for example ladybirds to eat aphids in glasshouses.Worked example: A crop has an NPP of 20 000 kJ m−2 yr−1. Insect pests eat 15% of it. An insecticide reduces this to 3%. Energy available for harvest rises from 17 000 to 19 400 kJ m−2 yr−1, a gain of 2400 kJ m−2 yr−1.Chemical pesticides act quickly, but they can kill non-target species, pests can evolve resistance, and some persistent pesticides accumulate along food chains. Biological control is more specific and pests rarely become resistant, but it is slower and does not remove the pest completely. Many farmers combine the two in integrated pest management.Simplifying food webs also reduces biodiversity, which is a cost to the wider ecosystem.
• Insecticides kill insect pests that eat the crop, so less of the crop's biomass (and energy) passes to non-human food chains.
• Fungicides kill fungi that cause crop diseases.
• Biological control uses a natural predator or parasite to reduce a pest population, for example ladybirds to eat aphids in glasshouses.Worked example: A crop has an NPP of 20 000 kJ m−2 yr−1. Insect pests eat 15% of it. An insecticide reduces this to 3%. Energy available for harvest rises from 17 000 to 19 400 kJ m−2 yr−1, a gain of 2400 kJ m−2 yr−1.Chemical pesticides act quickly, but they can kill non-target species, pests can evolve resistance, and some persistent pesticides accumulate along food chains. Biological control is more specific and pests rarely become resistant, but it is slower and does not remove the pest completely. Many farmers combine the two in integrated pest management.Simplifying food webs also reduces biodiversity, which is a cost to the wider ecosystem.