Most Northern Plains livestock producers are raising genetically improved modern high performance cattle, however, these cows and calves do not perform at their genetic potential after mid July. The grass herbage production drops 49.6% below the biological production level. The grass lead tiller nutritional quality falls below a lactating cows requirements after mid July. In order to regain some production, the cows are given access to lick tubs and the calves are provided creep feed.

These problems occur because the grasslands are low in mineral nitrogen. Intact grasslands contain large quantities of unavailable organic nitrogen. Grasslands are not low in nitrogen and the soils do not require supplemental nitrogen to be added. The traditional grazing practices prevent the mineralization of adequate quantities of organic nitrogen. 

Since the last climate change, that occurred around 5,000 years ago, grasslands have received by deposition at least 2 lbs of nitrogen per acre per year. Atmospheric nitrogen gas (N₂) is the original input source for grassland nitrogen. Our atmosphere is comprised of more than 78% nitrogen gas. There is about 34,500 tons of dinitrogen gas above an acre of land. The bonds that hold dinitrogen together are very strong. It requires the high temperature of lightning bolts at 50,000 °F to break these bonds. The freed nitrogen atoms can bond with oxygen to create nitrogen oxides and dinitrogen oxide that are deposited on soil with precipitation.

This nitrogen is rapidly assimilated to carbon forming immobilized organic compounds that are tied to the soil organic matter and are protected from loss by leaching or volatilization. Now, after 5,000 years, most intact, never plowed, grassland soils contain 5 to 6 tons of nitrogen per acre.

This huge amount of soil nitrogen is in the form of organic nitrogen that is not available for use by plants. Organic nitrogen must be mineralized by soil microbes before plants can use it. Grassland soils that are low in mineral nitrogen are also low in biomass of soil rhizosphere microbes.

While working at Sidney ARS during the 1970’s, Drs. Wight and Black discovered that in order for Northern Plains grasslands to produce herbage at biological potential, a threshold quantity of mineral nitrogen must be available at a minimum of 100 lbs/ac or greater.

The problem is that traditional grazing practices are designed to provide forage for livestock but they do not provide soil microbes at a large enough biomass to mineralize organic nitrogen at a rate of 100 lbs/ac. The soil rhizosphere microbes cannot increase their biomass on their own. They do not possess chlorophyll nor do they have access to sunlight, so they do not have the ability to fix carbon energy. The rhizosphere microbes require an outside source that can provide large quantities for short chain carbon energy before they can increase their biomass.

Some literature suggests that dead grass material could provide the needed energy, it cannot, it only contains 2% to 5% carbon energy. Other suggestions imply that plant leakage could provide the needed energy, but grass plants have low quantities of leakage that results in less than 20 lbs of mineral nitrogen per acre.

Fortunately, grass lead tillers capture and fix large quantities of surplus carbohydrate energy during the vegetative growth stages occurring during the early portion of their second year of development. Except, this surplus carbohydrate energy of the grass lead tillers is not naturally released into the soil.

Exudation of this surplus energy to move down through the roots into the microbial rhizosphere that surrounds the grass roots requires implementation of the biologically effective twice-over rotation strategy that provides the specific type of partial defoliation by large grazing graminivores that remove only 25% to 33% of the aboveground portion of the vegetative lead tillers after the 3.5 new leaf stage and before the flower stage during 1 June to 15 July. This particular treatment will cause the slow release of a sizable portion of the grass lead tiller surplus carbon energy to be transferred to the soil microbes.

This extremely important outside source of carbon energy will accommodate the rhizosphere microbes to increase their biomass. It usually requires about three growing seasons for the rhizosphere microbe biomass to become large enough so they can mineralize nitrogen at a rate of 100 lbs/ac or greater. 

After the increased biomass of soil microbes are able to provide 100 lbs of available mineral nitrogen per acre, the grassland herbage production increases 50.4% per inch of precipitation received, the livestock carrying capacity of grassland pastures increases 40%, the quantity of vegetative tillers greatly increase and provide adequate nutritional quality for lactating cows from July to mid October, cows continue to milk at or near their genetic potential during the entire growing season while they also gain weight, and calf weaning weight increases 60 to 65 pounds.

These ubiquitous problems caused by low mineral nitrogen when grasslands are managed by traditional grazing practices are eliminated when grasslands are managed by the biologically effective twice-over rotation strategy.