Is it Necessary to Apply That Much Fertilizer?
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Authors: Douglas Landblom, Larry Cihacek, and Songul Senturklu
Douglas Landblom,
DREC Beef Cattle and Integrated Systems Specialist
Dickinson Research Extension Center
Office: 701-456-1109; Mobil: 701-690-8245
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Virtually all farm commodity prices are rising. Drought in the western US has caused ranchers to sell portions and in some cases all of their cows. The result is a smaller national beef cow herd and demand for feeder cattle is pushing the price ranchers receive for their cattle higher. Likewise, grain and oilseed commodity prices have nearly doubled, i.e. corn $3.78 to $7.38, soybean $8.46 to $16.65, spring wheat (14% Pro) $5.09 to $9.78, and sunflower (NuSun) $19.61 to $35.35. While commodity price increases of this magnitude are remarkable, production input costs for fertilizer, chemicals, identity protected seed, fuel, repair, and equipment have not remained static, but have risen in response to the sharply higher commodity price. The question for farmers going into the 2022 cropping season is how much will the cost for inputs impact commodity breakeven. The USDA Economic Reporting Service tracks farm inputs for pesticide, fertilizer, fuel and oil, and electricity https://data.ers.usda.gov/reports.aspx?ID=17834. For the recent period between 2019 to 2022 (Est.), pesticide, fuel and oil, and electricity have not changed as dramatically as fertilizer, which is estimated to increase 42.9% and, perhaps, much more in various locations due to supply chain availability, freight, handling, margin increases, etc. Going further into the numbers, the same USDA ERS site reported total farm production expense (without dwellings) change between 2020 and 2021 and a projected increase between 2021 and 2022. Between 2020 and 2021 total farm expenses increased nationally 9.43% and is projected to increase another 5.14% between 2021 and 2022; a 14.6 % increase from 2020 to 2022. In addition to the escalating fertilizer price and increase in total farm expense is the potential for continued drought conditions in western ND.
Soil tests are a very important tool in the producer’s toolbox. Soil tests provide a measure of plant nutrients in the soil at the time the sample was collected; however, the test does not provide information with respect to nutrient mineralization due to microbial nutrient cycling that occurs during the growing season. At the Dickinson Research Extension Center, a long-term integrated crop and beef cattle grazing research study evaluated soil nitrogen mineralization and microbial biomass change during the 5-year crop production period (2011-2015). The crop rotation consisted of spring wheat, dual cover crop (fall planted winter triticale and hairy vetch harvested for hay in June followed by a 7-specie cover crop planted before July 1st), forage corn, field pea/forage barley mix, and oil-type sunflower. Spring wheat grown in the 5-crop diverse rotation (HRSW-R) was compared to a control treatment of spring wheat grown continuously on the same land year after year (HRSW-C). Legumes in the cover crop mixes and pea-barley mix fix N for subsequent crops. By comparison to the other annual crops, peas are a low water use crop and are placed in the rotation preceding sunflower, which is a high water use crop. Sunflower is also a deep nutrient mining crop, extends roots as deep as five feet into the soil profile extracting nutrients and water that shallow rooted crops are unable to tap into.
Over the 5-year period, urea nitrogen fertilizer applications were completely removed after the second year of the study in the HRSW-R treatment and after the third year in the HRSW-C treatment. The average HRSW yield did not differ between treatments as the 5-year yields were 42.1 vs. 42.5 for the HRSW-C and -R, respectively. Although average yield was virtually identical, averages do not explain yearly yield changes over time as related to soil nitrogen mineralization and yield shift during the five-year period. Figures 1 and 2 illustrate HRSW yields for control and rotation treatments, which have very different trends over time. When urea was applied, the HRSW-C treatment out yielded the HRSW-R treatment. However, when urea as the exogenous N source was removed, yield declined. At the same time, the HRSW-R yield grown without exogenous urea N continued to increase. By the fifth year (2015), HRSW-R yield was 15 bu./ac greater than the continuous HRSW-C treatment. How does this occur? Soil microbial activity is a very complex science. Nonetheless, in simple terms soil microbial nutrient cycling renders a wide array of readily available plant nutrients and nitrogenous compounds essential for plant growth (ammonium-N and nitrate-N) as byproducts of their respiration. Soil microbial activity is especially important for all plant growth, because plants are unable to obtain nutrients directly from soil organic matter (OM). Thus, soil microbial processing of OM is necessary to supply inorganic compounds to the soil solution for plant uptake. Assisting plant roots in the uptake of nutrients are fungal networks that develop in undisturbed soil. Mycorrhizal fungi form networks of microscopic hyphae that communicate with roots and enhance root capability to uptake nutrients, especially phosphorous. Nitrogen mineralization studies conducted by our research group (Cihacek et al., 2016) have identified potential N mineralization with respect to soil OM percent (Figure 3). Soil organic matter is food for soil microorganisms and, as such, as the amount of OM available for mineralization increases, a point is reached whereby fertilizer application is no longer required for maximum economic yield. Figure 3, summarizes nitrogen mineralization results from the HRSW control and crop rotation research. Our research group determined that a conservative estimate of nitrogen mineralization under the conditions of this research in the semi-arid environment of western North Dakota to be 15 to 17 lbs. of N for each 1.0% increase in soil OM, i.e. 1.0% = 17, 2.0% = 34, 3.0% = 51, 4.0% = ’68, and 5.0% = 685 lbs. N/ac, respectively. Of course, to obtain this level of N mineralization the soil must receive adequate precipitation during the growing season. Therefore, soil water is the first limiting nutrient. Based on soil test soil OM content, the amount of N fertilizer can be reduced accordingly. Because microbes do not readily function actively in cold soil, a starter fertilizer is recommended to boost early plant growth until soil temperature reaches critical activity temperature of approximately 60° F (60-85°F most favorable range). Therefore, based on soil OM content, N fertilizer application in western North Dakota may be reduced up to 40-50% without negatively impacting maximum economic yield.
Looking ahead to my next update, forage toxicities in will be discussed as related to the interaction between too little precipitation (drought) and too much precipitation, which unfortunately both environmental situations can cause nutritional problems for livestock.
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