Nitrogen

Nitrogen is a key element in protein formation. Nitrogen is valuable for growth and for proper body functioning. An intake of nitrogen in deficient plants is most noticeable by an increase in the size and greenness of leaves. Some Saskatchewan wheat is graded by protein content.

Roots absorb nitrogen mainly in the form of nitrate ions (also some ammonium). Certain bacteria change the nitrogen into the usable form by the processes of ammonification and nitrification.

Losses:

• Crop removal - A wheat crop of 2000 kg/ha will remove about 50 kg of N/ha in the grain. A 2000 kg/ha crop of canola will remove as much as 70 kg of N/ha in the seed
• Burning Straw - If we burn the straw from our 2000 kg/ha wheat crop, we will lose 15 kg N/ha to the atmosphere.
• Volatilization - Fertilizers such as ammonia or urea can be lost when unfavourable soil conditions exist. For example if urea is applied to a soil surface with trash cover and the soil is dry, up to 40% can be lost before the rest of the urea is washed into the soil.
• Denitrification - Under waterlogged conditions in the presence of organic matter, soil microorganisms (autotrophs) can covert soil nitrate to nitrogen gases such as NO, N₂O and N₂ which are lost to the atmosphere.
• Leaching - Urea fertilizer and soil nitrate are very mobile in soil solution and can be washed down the soil profile by heavy precipitation. Much of this nitrogen finds its way into aquifers, streams and lakes contaminating waterways and drinking water. Great care is need in applying fertilizer nitrogen so that this source of pollution is minimized.

Additions:

1. Non-Symbiotic N-fixation - by lightning and free living soil organisms. Worldwide this is an important source of nitrogen, but in Saskatchewan it amounts to only 5-10 kg N/ha per year.
2. Symbiotic Fixation - by legumes can amount to more than 100 - 200 kg/ha per year. Alfalfa fixes the largest amounts, red clover the least. Pulse crops fix less N, in the 50 -100 kg/ha range. Faba beans fix the largest amounts.
3. Fertilizers - Deficiencies in nitrogen have to made up for in the addition of natural or chemical fertilizers. Farmers in Saskatchewan typically apply up to 100 kg N/ha on stubble lands and much less or no nitrogen to grow cereals on summerfallow land. How do we know how much N to add? Most Saskatchewan soils are tested regularly by farmers for available soil nitrogen levels.

Phosphorus

Phosphorus is essential for the early maturity of crops and for root growth. Small seedlings, especially, benefit from a good phosphorus supply. Phosphorus is the most immobile of the macronutrient elements. If we placed a pellet of phosphorus fertilizer in the soil we would not expect the phosphorus from the pellet to move more than a cm or so. Since phosphorus is not as soluble or as mobile as nitrogen, it is not as easily leached out of the soil. Since roots literally have to grow into the zones where the fertilizer has been placed, poorly placed fertilizer, too far from the seed, may result in phosphorus deficiency to the seedlings. Phosphorus that is added to soil as soluble fertilizer in the form of the orthophosphate anions H₂PO₄ ^- and HPO₄^2- is converted over time to more insoluble and less available forms such as apatite. Most Saskatchewan soils need regular phosphorus additions and phosphorus analysis is part of a normal soil or plant test. The most effective way to apply phosphorus fertilizer is with the seed or seed placed. A rate of 20 to 30 kg/ha of 11-55-0 as P2O5 is usually sufficient to supply the crop. Phosphorus fertilizers give a so called pop-up effect when seeds germinate in cool damp conditions. phosphorus placed close to the germinating seed allows for rapid root growth and seedlings will emerge faster than those with no fertilizer.

Potassium

Potassium is utilized by a plant in the development of strong stems. This macronutrient also assists the plant in obtaining a higher tolerance to disease and helps to assist the plant in its use of water. Most potassium in plants is found in the above ground portion of cereal and oilseeds, mainly in the straw. Therefore, if crop residues are returned to the soil, a good proportion of the potassium is conserved. In soils, potassium is found as part of the mineral structure of many clay minerals particularly micas. In this form, however, it is locked away from plant roots. The other forms of potassium that are available are part of the K⁺ cations on the soil exchange complex and in solution.

Potassium fertilization is not common in most Saskatchewan soils. Certain sandy soils in the Gray-Black and Gray soil zones have benefited from the addition of Potassium particular when crops such as barley are grown. Most of the potash ore mined in Saskatchewan is exported giving the Province a valuable industry.

Sulphur

Plants such as canola, mustard, forage legumes and annual legumes (peas, lentils...). produce a large amount of protein in their tissues and seeds. Protein synthesis not only needs nitrogen and phosphorus, but also require large amounts of sulphur. In addition to protein synthesis, sulphur is necessary for essential oils in brassicas and onions and for some enzyme actions and general growth. A number of agricultural practices decrease the levels of this element. Higher moisture levels, which increase leaching, carry the more soluble sulphates salts out of the upper soil zones. Microbial actions to replace these sulphur compounds are normally slow and have decreased even further with minimum tillage practices. Heavier straw and stubble covers lead to upper soil layers being cooler and more moist. Both conditions slow down microorganisms and sulphate formation. Heavier stands (growths) of alfalfa, clover and canola can remove enough sulphur in a growing season to noticeably affect next season's stand, especially if it is of a legume or mustard family. Many soils in the Black and Gray soil zones are deficient in sulphur and a few soils in the Dark Brown and Brown soil zones. The deficiency will spread as we continue to lose large amounts of this nutrient in annual crops and leaching. Which soils in the province will never need sulphur fertilization - the saline soils? Why?