Nutrient Management

This chapter discusses the mineral nutrition of crops. Plants use energy from the sun to fix carbon dioxide from the atmosphere in photosynthesis. The nutrient cycle of the soil is seen when bacteria and fungi break down organic matter to release minerals, ammonium, and nitrate so that they can be taken up again by bacteria and fungi. Plants have roots that take up that ammonium and nitrate for plant growth; when the plants die, they become the organic matter that is broken up. The plant products and animal products become food for us, and that is where the cycle gets broken, because humans use toilets and do not return the organic matter to the land. An example of a closed nutrient cycle is the rainforest, which has very little input and output because there is internal cycling. An open nutrient cycle could be found on an intensive pig farm where feed is purchased and meat and manure are sold. Outputs must be balanced by inputs. In total, plants need 13 elements from the soil, most importantly, nitrogen, phosphorus, and potassium. The nitrogen cycle is biological and is carried out by legume crops. Phosphorus and potassium have chemical cycles. Nitrogen is lost in its cycle, to the atmosphere through volatilization of ammonium or denitrification of nitrate and nitrate is leached from the soil, causing issues of global warming and water contamination. We need to practice better nutrient stewardship using the four ‘R’s; using the right source of nutrients, the right composition, the right rate of application, and the right place for application. Nutrient fertilization can be reduced to avoid eutrophication problems, but in some areas of the globe, more fertilizers must be apples to produce the food we need. We must think about mixed farming systems, in which for example, the manure from one farm can actually be the nutrient resource for another. Organic agriculture would only feed about 1/4 of the planet if it were applied universally because there aren’t enough nutrients, and it is difficult to apply the nutrients at the right time in the right amount. The bottom line is integrated soil fertility management. 

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