Nutrients in Agriculture

Topics Basic plant physiology Types of nutrients systems Relation between fertilizer use and production Amount of fertilizer used World supply of fertilizer Fates of fertilizer in the biosphere Dead zones and associated controversy Other environmental impacts of fertilizers Key messages

Plant physiology Plants must obtain the following mineral nutrients from the growing media: [2] [2] the primary macronutrients: nitrogen (N), phosphorus (P), potassium (K) the three secondary macronutrients such as calcium (Ca), sulphur (S), magnesium (Mg). the macronutrient Silicon (Si) and micronutrients or trace minerals: boron (B), chlorine (Cl), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo), nickel (Ni), selenium (Se), and sodium (Na).molybdenum

Types of nutrient systems Pre-industrial manure cycles and crop rotation Organic fertilizers Industrial Fertilizers Organic Farming

Medieval European Agriculture Plowing done with an ox or horse, harvest by hand Nutrients supplied by animal manure, human manure and fallowing the ground every 2 nd or 3 rd year, sometimes planted with legumes. Plowing plants back into the ground to fertilize the ground is known as “green manure” Grain production about 1/5 per ha of current yields. Yield was about 4 seeds per seed planted.

The Black Death

Agricultural consequences of plague in Europe About 1/3 of people died – human density reduced Price of labor to landlords increased More land per person – more land could be devoted to animals, more manure available, more fallow and pasture Soil building and higher yields

Rice culture in the past, traditional rice farmers in Asia used raw organic matter, human and animal manures, ashes, fish bone and other waste materials to make the rice plant more productive. Compost and green manures had also widely used. Compost was a major factor for farmers to win in yield contests organized in Japan during In many countries green manure is regarded as an important nutrient source for rice.

Other sources Native Americans used fish Seaweed

Natural sources Guano Phosphate

Guano Bird droppings rich in phosphate and nitrogen. the US passed the Guano Islands Act in 1856 giving citizens discovering a source of guano the right to take possession of unclaimed land and entitlement to exclusive rights to the deposits.

Phosphate rock Many rocks are naturally rich in phosphate This can be mined and used as fertilizer

The collapse of Nauru Small Island consisting primarily of phosphate

The collapse Once called the Kuwait of the Pacific 10,000 people had $1 Billion in assets Nauru Hotel in Honolulu Lost it all due to bad financial management The island is a hollow shell, stripped clean Ended up taking “boat people” Australia didn’t want in order to get some funds

Artificial fertilizer

History Haber and Bosch were awarded the Nobel Prize for method to produce industrial ammonia from atmospheric nitrogen and natural gas. This process forms the basis for almost all industrial nitrogen fertilizers, uses 1-2% of world energy supply Rock based phosphates are often added in modern fertilizer

Global supply

The Phosphate Famine

Environmental Impacts Eutrophication Soil acidification Persistent organic pollutants Heavy metal accumulation Radioactive element accumulation

From farm to water 20% lost through surface runoff and leaching Volatilization is transfer of nitrogen to the air from crops and manure, and this nitrogen is subsequently deposited on land and water

Gulf of Mexico Dead Zone

What is a dead zone: Gulf of Mexico An seasonal or permanent zone of low oxygen concentration Caused by bacterial action consuming the available oxygen Nitrogen and phosphorus come almost exclusively from river discharge which have increased 3 fold for phosphorus and 8 fold for nitrogen compared to pre-industrial inputs

Other dead zones Often natural caused by changes in ocean circulation through upwelling

Small group discussion What could be done to reduce the dead zones in the Gulf of Mexico Who would do it?

Soil acidification Some soils are naturally acidic Many fertilizers increase soil acidity, reducing productivity for many crops Adding lime is a common remedy for acid soils

Persistent organic pollutants Organic chemicals that are resistant to degradation They are found in some fertilizers and accumulate in the soils can health impacts in high concentrations

Heavy metal accumulation A number of fertilizers have trace amounts of heavy metals such as cadmium, zinc, lead and arsenic This do not degrade and accumulate

Radioactive element accumulation Some phosphate fertilizers contain radioactive uranium, that accumulate in soils

Nutrients in organic farming Compost Crop rotation Cover crops of legumes that are plowed back (called green manure) Animal manure

Key messages Nutrients are essential to food production Increase in yields has been significantly due to added inputs of nutrients These nutrients have significant environmental impacts Human health impacts always need to be balanced against the benefits of higher yields

Study guide What are the three primary macronutrients needed for plant growth? Nitrogen, phosphorus and potassium What were the major sources of nutrients in pre-industrial European agriculture? Animal manure, human manure, green manure. What was the major impact of the Black Death on European agriculture? Population density was reduced so that there was more land available for animals, leading to more manure, leading to higher crop yields and soil building. What are two natural forms of industrial scale fertilizer. Bird guano and natural phosphate deposits. What is the role of the nation of Nauru in agriculture? It was once the source of rich phosphate deposits. What was the major scientific discovery that stimulated the modern fertilizer industry? The development of the Haber-Bosch process for converting atmospheric nitrogen and natural gas to ammonia. What are the major concerns about the impact of artificial fertilizers on the environment and soils? Eutrophication Soil acidification Persistent organic pollutants Heavy metal accumulation Radioactive element accumulation What is volatilization? Volatilization is transfer of nitrogen to the air from crops and manure, and this nitrogen is subsequently deposited on land and water. What is a dead zone? A region of the ocean with very low oxygen concentration. How do fertilizers contribute to soil acidification? Many fertilizers are naturally acidic making the soil more acidic.