Browsing by Author "Macnack, Natasha"

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    Effect of Fertilizer Nitrogen (N) on Soil Organic Carbon, Total N and Soil Ph in Long-Term Continuous Winter Wheat (Triticum Aestivum L.)
    (Communications in Soil Science and Plant Analysis, 2016) Aula, Lawrence; Macnack, Natasha; Omara, Peter; Mullock, Jeremiah; Raun, William
    Carbon sequestration via sound agronomic practices can assist in combatting global warming. Three long-term experiments (Experiment 502, Experiment 222, and The Magruder Plots) were used to evaluate the effect of fertilizer nitrogen (N) application on soil organic carbon (SOC), total nitrogen (TN) and pH in continuous winter wheat. Soil samples (0-15 cm) were obtained after harvest in 2014, analyzed and compared to soil test results from these same experiments in 1993. Soil pH decreased with increasing N fertilization, and more so at high rates. Nitrogen application significantly increased TN in Experiment 502 from 1993 to 2014, and TN tended to be high at high N rates. Fertilizer N significantly increased SOC, especially when N rates exceeded 90 kg ha-1. The highest SOC (13.1 g kg-1) occurred when 134 kg N ha-1 was applied annually. Long-term N application at high rates increased TN and SOC in the surface soil.
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    Effect of Long-term Beef Manure Application on Soil Test Phosphorus, Organic Carbon and Winter Wheat Yield
    (Journal of Plant Nutrition, 2017) Omara, Peter; Macnack, Natasha; Aula, Lawrence; Raun, Bill
    In this study, 24 years (1990-2013) of data from a long-term experiment, in Stillwater, Oklahoma (OK) were used to determine the effect of beef manure on soil test phosphorus (STP), soil organic carbon (SOC) and winter wheat (Triticum aestivum L.) yield. Beef manure was applied every four years at a rate of 269 kg nitrogen (N) ha-1 while inorganic fertilizers were applied annually at 67 kg N ha-1, 14.6 kg phosphorus (P) ha-1, and 27.8 kg potassium (K) ha-1 for N, P and K, respectively. Averaged across years, application of beef manure and inorganic P maintained STP above 38 mg kg-1 of Mehlich-3 extractable P, a level that is far beyond crop requirements. A more rapid decline in SOC was observed in the check plot compared to the manure treated plot. This study shows that application of animal manure is a viable option to maintaining SOC levels while also optimizing grain yield.
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    Effect of Seed Distribution and Population on Maize (Zea mays L.) Grain Yield
    (International Journal of Agronomy, 2014) Chim, Bee Khim; Omara, Peter; Macnack, Natasha; Mullock, Jeremiah; Dhital, Sulochana; Raun, William
    Maize planting is normally accomplished by hand in the developing world where two or more seeds are placed per hill with a heterogeneous plant spacing and density. To understand the interaction between seed distribution and distance between hills, experiments were established in 2012 and 2013 at Lake Carl Blackwell (LCB) and EfawAgronomy Research Stations, near Stillwater, OK. A randomized complete block design was used with three replications and 9 treatments and a factorial treatment structure of 1, 2, and 3 seeds per hill using interrow spacing of 0.16, 0.32, and 0.48m. Data for normalized difference vegetation index (NDVI), intercepted photosynthetically active radiation (IPAR), grain yield, and grain N uptake were collected. Results showed that, on average, NDVI and IPAR increased with number of seeds per hill and decreased with increasing plant spacing. In three of four site-years, planting 1 or 2 seeds per hill, 0.16m apart, increased grain yield and N uptake. Over sites, planting 1 seed, every 0.16m, increased yields by an average of 1.15Mgha−1 (range: 0.33 to 2.46Mg ha−1) when compared to the farmer practice of placing 2 to 3 seeds per hill, every 0.48m.