Digitized by Kansas Correctional Industries

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Call number: LD2668 .T4 1956 S42 / Master of Science

Fertilizer applications of urea and triple superphosphate (TSP) may affect availability of plant nutrients in the soil through alteration of soil pH and sorption-displacement effects. The objectives of this experiment were to evaluate urea and TSP effects on nutrient availability to soybean (Glycine max L.). Field experiments were carried out on three Quebec soils; a Chicot sandy clay loam (Gleyed Melanic Brunisol), an Ormstown silty clay loam (Luvic Gleysol) and a Ste. Rosalie clay (Humic Gleysol). Three levels of TSP (0, 40, 80 kg $ rm P sb2O sb5 ha sp{-1}),$ and three levels of urea (0, 25, 50 kg N ha$ sp{-1})$ were incubated in the field and sampled at 4, 8, 12, and 16 weeks. Added TSP increased extractable P and decreased NO$ sb3$-N. Overall, alterations in nutrients other than N and P with added TSP or urea were not agronomically significant. There was increased concentration of N, P and Mo in soybean in some soils due to TSP application. Added urea increased Mg concentration in soybean. The concentration and uptake of Mo was positively correlated with soil extractable P and Mg. Consequently, application of TSP and urea together improved Mo uptake in the Chicot soil, while in slightly acid soils, Ormstown and Ste. Rosalie, TSP alone increased Mo uptake.

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The effect of applied B, Cu, Mn and Zn on soybean seed yield and tissue micronutrient concentration was studied under different field conditions. Manganese application increased soybean seed yield on the Dragston, Myatt and Slagle fine sandy loams, but not on Rains fine sandy loam. Seed yield was not affected by applied B, Cu or Zn. Broadcast and foliar Mn applications were similarly effective in correction of Mn deficiency and, among foliar Mn applications, split application resulted a higher seed yield than single applications. Micronutrient concentration of the leaf blades, petioles and seeds was increased with the application of B, Cu, Mn and Zn. The increase in tissue B concentration was much greater than that of the other micronutrients. Broadcast Mn application resulted in a higher tissue Mn concentration than foliar Mn applications. The critical Mn concentration in leaf blades at the R1 growth stage was above the level of 13 µg/g, which is reported in the literature. It was concluded that the present calibration of the dilute HC1-H₂SO₄ extractable Mn soil test overpredicts the incidence of Mn deficiency in soybeans. / Master of Science

Fertilized croplands unintentionally export large amounts of reactive nitrogen (N), which degrades water and air quality and contributes to climate change. In this dissertation, I focus on how these reactive N losses are likely to change in the near future as agriculture intensifies in the tropics, and ecological intensification strategies to mitigate N losses are more widely adopted. I use a combination of empirical field measurements in Mato Grosso, Brazil and Skåne, Sweden, literature review, and statistical models to quantify trends. In chapter one, I quantified emissions of nitric oxide (N₂O) and nitrous oxide (N₂O) in forest, single cropped soybean, and N-fertilized double-cropped soybean-maize at three nitrogen fertilizer levels within the largest area of recent cropland expansion on earth, in the Amazon and Cerrado biomes in Mato Grosso, Brazil. I found that NO emissions do not increase when forests are converted to croplands under current fertilization levels, and that NO will respond more strongly than N₂O fluxes to increases in fertilizer applications. In chapter two, I investigated anion exchange capacity and soil nitrate (NO₃¯) pools in deep soils in Mato Grosso, Brazil in the southern Amazon. I found that soil NO₃¯ pools in the top 8 m increased from 143 kg N ha¯¹ in forest to 1,052 and 1,161 kg N ha¯¹ in soybean and soybean-maize croplands. This NO₃¯ accumulation in croplands compared with forest soils matched the estimated amount of surplus N from the croplands, and could be explained by the soil’s positive charge through its anion exchange capacity. In chapter three, I conducted a meta-analysis of the effects of fertilization amount on of NO₃¯ leaching, N₂O emissions, NO emissions, and ammonia (NH₃) volatilization, totaling over 1,000 observations. I found that the relationship between N inputs and losses differed little between temperate and tropical croplands, although total NO losses were higher in the tropics. Among the potential drivers I studied, the N input rate controlled all N losses, but soil texture and water inputs also controlled NO₃¯ leaching losses. In chapter four, I explored the differences in NO₃¯ leaching, fertilizer N use efficiency, and soil N cycling in perennial wheat, which is being domesticated as a more sustainable alternative to annual crops, and annual wheat at a long-term experimental site in Skåne, Sweden. I found that NO₃ leaching was more than two orders of magnitude lower in perennial wheat, overall ecosystem recovery of fertilizer was quite high and not significantly different between perennial and annual wheat after the first growing season, and that measures of soil N cycling were largely the same between both crops. Together, these chapters highlight that reactive N losses will remain a critical global challenge in the coming decades, but that there are also key opportunities to reduce N losses by increasing the use of perennial crops and focusing tropical agricultural intensification on Oxisol soils which buffer against NO₃¯ leaching.

Soil phosphate is essential for the development and maturity of crops. Plants absorb phosphate from the soil solution which is continuously replenished by fertilizer application and/or desorption from the soil solid phase. Anion exchange membranes (AEMs), act in a similar way to plant roots, adsorbing P from soil solution. Desorption of available P was studied in 1997 on two Gleysolic soils rich in P, a Ste. Rosalie clay soil and a Duravin sandy loam soil, using fluoride-saturated AEMs let in soil suspension for various contact periods. Determination of available P using these AEMs was compared to P extraction using the Mehlich III extractant for predicting P availability to soybean (Glycine max L.). Desorption from both soils, and subsequent adsorption by AEMs was found to decrease with time. A high P desorption rate was calculated for both soils with the Elovich equation. Different chemical and physical characteristics such as pH, Mehlich III extractable Al, Fe and Ca, sand and clay content were in some cases, positively correlated and in other cases, negatively correlated with various contact periods for both soils. The use of AEMs better predicted P availability than the Mehlich III extractant, although the most important asset of using AEMs is that they showed the desorption effect over time on P availability. It was observed that P remobilization from the vegetative part to the grain was reduced due to the high P concentration in both soils.

Corn (Zea mays L.) production under monoculture and conventional-tillage management may cause soil degradation and nitrate (NO$ sb3 sp-)$ pollution. This study was conducted from 1991 to 1993 to evaluate the impact of conventional-tillage (CT) and no-tillage (NT) practices under corn-soybean (Glycine max L. Merill) rotations (C-S-C and S-C-S), continuous corn (C-C-C) and continuous soybean (S-S-S) systems on optimum N fertilization rates, yield and soil residual N levels. Field experiments were carried out on a Ste. Rosalie clay (Humic Gleysol) and an Ormstown silty clay loam (Humic Gleysol). Overall, tillage had little effect on soil and crop N levels or grain yields. Residual soil NO$ sb3$-N in the fall was related to fertilizer N rates in C-C-C, but not with S-S-S or soybean in rotation. Residual NO$ sb3$-N values after soybean were high and at zero added N were equivalent to 90 kg N with C-C-C. Consequently, soybean contributed the equivalent of 90 kg N ha$ sp{-1}$ to subsequent corn. Corn yields following soybean were higher than following corn, and less fertilizer N was required following soybean than following corn.