45 Story Idea?Email Paul.Nolan@Farms.com Better Farming | November 2023 to a half-pound of boron side-dressed in 28 per cent nitrogen on lighter textured soils. e zinc (Zn) results showed 20 per cent of the samples as de cient. Application of Zn on corn is easily accomplished by applying it in starter fertilizers. e relationship between phosphorus (P) and Zn antagonism is well noted as high P precipitates Zn from soil solution. A Zn soil test is a good indicator of Zn supply. I have not fully analyzed the sites for fertility programs to determine the Zn application status. e most notable de ciency was 80 per cent of the corn samples de cient in magnesium (Mg). O en the rst thought on Mg de ciency is low soil pH, which leads one to think of the need for limestone to adjust the pH and using dolomitic lime to increase the Mg level. is is a valid concern but not in this case; all the elds had a pH over 6.5. And in all cases, the soil test level of Mg was 150 to 250 ppm. e base saturation of Mg was 10 to 14 per cent, typical of most soils in Ontario. We can rule out low pH and low soil test levels. Mg uptake is predominately by mass ow and a small portion by root interception. To support mass ow, there needs to be moisture available to move nutrients to roots to support transpiration. e nutrients are carried in the soil solution to the root surface for absorption. Under dry conditions, this mechanism is less e ective and could well explain low nutrient uptake. However, potassium (K) and calcium (Ca) move in the same manner and were not deemed de cient except for 8.5 per cent of samples de cient in K. What else explains the lack of magnesium uptake? We need to look at antagonism and stimulation factors that can impact Mg uptake. Mulder’s Chart is o en cited as o ering some explanations on nutrient interactions. Although designed mostly for nutrient solutions, it does have some merit in soil solution interactions. Soils do complicate nutrient uptake with di erent soil textures, pH, mineralization, immobilization, adsorption and desorption rates of nutrients from clay surfaces. From a stimulation standpoint, P can stimulate Mg uptake. A shortage of P can reduce Mg uptake especially if the level of Mg is also low. Ammonium N found in monoammonium phosphate (MAP) fertilizer stimulates P uptake and therefore Mg uptake. Ammonium N that’s not associated with MAP suppresses Mg uptake while nitrate N does not to the same degree. From an antagonism standpoint, a relationship between soil test K and Mg exists. My observation is when soil test K is greater than soil test Mg, there is a suppression of Mg uptake (and lower P uptake). I’ve o en seen a delayed maturity in the crop, especially in corn. I see the most Mg issues on livestock farms due to manure applications. Manure is o en high in K and low in Mg. Sandier low CEC soils with low bu ering capacity are also supportive of high K:Mg ratios. Grass tetany is a nutritional disorder of mostly cows that experience a low level of Mg in their blood. Grass forages heavily fertilized with potash can suppress dietary uptake of Mg. A low content of Mg in the forage can contribute to the issue. It is a serious disorder and great care is needed when feeding fresh grass and forage cereals that will have elevated levels of K in early vegetative growth stage. Another antagonism is elevated levels of Ca in the soil that can at times suppress Mg uptake. is is normally crops: yield matter$ Mulder’s Chart We appreciate all your comments, along with story ideas on issues you want to see us cover. Paul.Nolan@Farms.com HOW ARE WE DOING?
RkJQdWJsaXNoZXIy NTc0MDI3