Peter P. Motavalli

Challenges and opportunities for mitigating nitrous oxide emissions from fertilized cropping systems

Nitrous oxide (N2O) is often the largest single component of the greenhouse-gas budget of individual cropping systems, as well as for the US agricultural sector as a whole. Here, we highlight the factors that make mitigating N2O emissions from fertilized agroecosystems such a difficult challenge, and discuss how these factors limit the effectiveness of existing practices and therefore require new technologies and fresh ideas. Modification of the rate, source, placement, and/or timing of nitrogen fertilizer application has in some cases been an effective way to reduce N2O emissions. However, the efficacy of existing approaches to reducing N2O emissions while maintaining crop yields across locations and growing seasons is uncertain because of the interaction of multiple factors that regulate several different N2O-producing processes in soil. Although these processes have been well studied, our understanding of key aspects and our ability to manage them to mitigate N2O emissions remain limited.

Soil phosphorus fractions after 111 years of animal manure and fertilizer applications

Abstract. Accumulated soil P in agricultural soils is a major source of soluble and particulate forms of P entering water resources and degrading water quality. However, few research sites are currently available to evaluate the long-term effects of different cropping systems and fertility practices on soil inorganic and organic P accumulation. The objectives of this study were: (1) to compare the forms and quantity of different inorganic and organic soil P fractions in plots on Sanborn Field, which has been cultivated for 111 years; and (2) to assess the use of standard soil test P extractants for determining changes in soil P dynamics over time. A modified sequential P extraction procedure was used to separate labile and stable inorganic and organic P pools from surface soils collected on Sanborn Field in 1915, 1938, 1962, and 1999 from plots in continuous corn, continuous wheat, continuous timothy, and a corn–wheat–clover rotation amended with either manufactured fertilizers, horse or dairy manure or receiving no fertilization since 1888. Additional samples were collected from a native grass prairie site of a similar soil series to estimate soil characteristics at Sanborn Field before initial cultivation in 1888. Observed accumulation of Bray-1 P among fertilizer and manure treatments was attributed to over-application of P due to unrealistically high yield goals for each cropping system. Long-term cultivation of Sanborn Field increased soil bulk density and lowered soil pH and total organic C compared with native prairie. Fertilization either by addition of manufactured fertilizer or manure significantly increased inorganic resin-P and inorganic NaOH-extractable P. Applications of animal manure also significantly increased most organic P fractions compared with the unfertilized treatment. The native prairie had a larger proportion of total P in organic forms compared with cultivated plots, especially in organic NaOH-extractable P, but no significant decreases in either residual or total P were observed due to cultivation. This study confirms that soil P availability in cropping systems that are amended with predominantly organic P amendments may differ from conventional cropping systems relying on manufactured P fertilizers. However, no direct evidence was found to support the hypothesis that any individual inorganic or organic soil P fraction has a better relationship than conventional soil test P extractants with plant P uptake under contrasting organic and conventional fertility practices.

Bacterial diversity in rhizospheres of nontransgenic and transgenic corn.

ABSTRACT Bacterial diversity in transgenic and nontransgenic corn rhizospheres was determined. In greenhouse and field studies, metabolic profiling and molecular analysis of 16S rRNAs differentiated bacterial communities among soil textures but not between corn varieties. We conclude that bacteria in corn rhizospheres are affected more by soil texture than by cultivation of transgenic varieties.

Differences in yields, residue composition and N mineralization dynamics of Bt and non-Bt maize

Cultivation of genetically modified crops may have several direct and indirect effects on soil ecosystem processes, such as soil nitrogen (N) transformations. Field studies were initiated in Northeast Missouri in 2002 and 2003 to determine grain and biomass yields and the effects of application of crop residues from five Bt maize hybrids and their respective non-Bt isolines on soil inorganic N under tilled and no-till conditions in a maize-soybean rotation. A separate aerobic incubation study examined soil N mineralization from residue components (leaves, stems, roots) of one Bt maize hybrid and its non-Bt isoline in soils of varying soil textural class. Three Bt maize hybrids produced 13–23% greater grain yields than the non-Bt isolines. Generally no differences in leaf and stem tissues composition and biomass was observed between Bt and non-Bt maize varieties. Additionally, no differences were observed in cumulative N mineralization from Bt and non-Bt maize residues, except for non-Bt maize roots that mineralized 2.7 times more N than Bt maize roots in silt loam soil. Incorporation of Bt residues in the field did not significantly affect soil inorganic N under tilled or no-till conditions. Overall Bt and non-Bt maize residues did not differ in their effect on N dynamics in laboratory and field studies.

The impact of land clearing and agricultural practices on soil organic C fractions and CO2 efflux in the Northern Guam aquifer

The importance of the Northern Guam aquifer as a source of drinking water for the tropical Pacific island of Guam has stimulated public interest in the impact of forest clearing and conversion to agriculture on the region’s environment. The objectives of this study were to determine the effects of land clearing, tillage, and fertilization of tropical secondary forest on soil organic and organic C fractions in the shallow, calcareous soil that overlies most of Northern Guam. A field experiment was established on a secondary forest site in Northern Guam to simulate land clearing, cultivation and fertilization with two separate applications of N, P and K fertilizer or leucaena (Leucaena leucocephala(Lam.) de Wit) leaves. Initial aboveground biomass of secondary forest was relatively low in comparison to that of other moist tropical forest sites, possibly because of poor soil fertility, shallow soil depth, and frequent natural disturbance from tropical storms. Rates of litterfall were also affected by the high winds associated with storm activity. Clearing, cultivation and fertilization over a 325-day period significantly reduced microbial biomass C. Soil surface CO2 efflux was characterized by short-term flushes shortly after tillage and was affected by soil moisture content and possibly by the proportion of active organic C contained in the soil. A comparison of commercial fields with continuous cultivation histories of 1‐26 years and forest sites in Northern Guam showed approximately a 44% decrease in soil organic C within 5 years after conversion of secondary forest to continuous cultivation. Further information is needed on the effectiveness of minimum tillage, application of organic amendments, or improved crop residue management to maintain soil organic C in Northern Guam.

Phosphorus and Nitrogen Sorption to Soils in the Presence of Poultry Litter-Derived Dissolved Organic Matter

Two environmental aspects associated with land application of poultry litter that have not been comprehensively evaluated are (i) the competition of dissolved organic matter (DOM) and P for soil sorption sites, and (ii) the sorption of dissolved organic nitrogen (DON) relative to inorganic nitrogen species (e.g., NO(3)(-) and NH(4)(+)) and dissolved organic carbon (DOC). The competition between DOM and P for sorption sites has often been assumed to increase the amount of P available for plant growth; however, elevating DOM concentrations may also increase P available for transport to water resources. Batch sorption experiments were conducted to (i) evaluate soil properties governing P sorption to benchmark soils of Southwestern Missouri, (ii) elucidate the impact of poultry litter-derived DOM on P sorption, and (iii) investigate DON retention relative to inorganic N species and DOC. Soils were reacted for 24 h with inorganic P (0-60 mg L(-1)) in the presence and absence of DOM (145 mg C L(-1)) using a background electrolyte solution comparable to DOM extracts (I = 10.8 mmol L(-1); pH 7.7). Soil P sorption was positively correlated with metal oxide (r(2) = 0.70) and clay content (r(2) = 0.79) and negatively correlated with Bray-1 extractable P (r(2) = 0.79). Poultry litter-derived DOM had no significant negative impact on P sorption. Dissolved organic nitrogen was preferentially removed from solution relative to (NO(3)(-)-N + NO(2)(-)-N), NH(4)(+)-N, and DOC. This research indicates that poultry litter-derived DOM is not likely to enhance inorganic P transport which contradicts the assumption that DOM released from organic wastes increases plant-available P when organic amendments and fertilizer P are co-applied. Additionally, this work demonstrates the need to further evaluate the fate and transport of DON in agroecosystem soils receiving poultry litter applications.

Evaluation of Continuous In Situ Monitoring of Soil Changes with Varying Flooding Regimes

Abstract To support investigations of flood tolerance occurring at a field‐based research facility, changes in soil volumetric water content, temperature, redox potential, dissolved oxygen content, and pH over the course of flood events were monitored. Electronic sensors connected to dataloggers for continuous monitoring of these parameters were installed, and soil redox potential and pH were also monitored manually for comparison. Soil volumetric water content showed that soils became saturated quickly following inundation. Soil redox potentials revealed a reduction of the soil with inundation; however, stagnant water treatments did not result in lower redox potentials than flowing water treatments. Similarly, dissolved oxygen content was not lower in the stagnant water treatment. The automated and manual systems detected similar trends in redox potential response to flooding; however, redox potentials measured manually were generally higher and significantly different from those obtained with the automated system. Anomalous readings were detected with the automated measurement of soil pH, indicating further need for improvement of this system.

Initial and residual effects of organic and inorganic amendments on soil properties in a potato-based cropping system in the Bolivian Andean Highlands.

The objective of this study was to determine the effects of applications of organic and inorganic soil amendments on initial and residual soil chemical, physical and biological properties that may affect both shortand long-term soil fertility in a potato (Solanum tuberosum L.)-based cropping system of indigenous rural communities in the Bolivian Andean Highlands (Altiplano). Field experiments were conducted in four representative low and high elevation communities in the semi-arid Central Andean Region of Bolivia from 2006 to 2009. Treatments included a control, and applications of sheep and cow manure, a commercial household/urban compost product, a commercial biofertilizer soil amendment, urea and diammonium phosphate and combinations of these different treatments. Soil samples were taken from all the sites prior to application of treatments and planting of potatoes as well as during the growing season and prior to planting of a Research Article American Journal of Experimental Agriculture, 2(4): 641-666, 2012 642 subsequent crop of quinoa (Chenopodium quinoa, Willd). Soil pH, soil total organic C, and total N increased due to application of organic fertilizers with or without inorganic fertilizers. Soil inorganic N and Bray-1 P were increased by inorganic fertilizers alone or when combined with organic fertilizers. The residual effect of most of the analyzed soil nutrients was detected in the subsequent growing season. In addition, lower soil bulk density was observed after organic fertilizers were applied with or without inorganic fertilizers and this residual effect persisted for the quinoa crop. In a controlled laboratory incubation experiment, soil potentially mineralizable C and N increased as organic fertilizers application rates rose from 0 to 30 Mg ha. These results highlight the importance of a balanced soil fertilization program in this region with use of optimum rates of both inorganic and organic soil amendments to increase shortand long-term soil fertility.

Reducing Phosphorus Loss in Tile Water with Managed Drainage in a Claypan Soil

Installing subsurface tile drain systems in poorly drained claypan soils to improve corn ( L.) yields could potentially increase environmental phosphorus (P) loss through the tile drainage system. The objectives of the study were to quantify the average concentration and loss of ortho-P in tile drain water from a claypan soil and to determine whether managed subsurface drainage (MD) could reduce ortho-P loss in tile water compared with free subsurface drainage (FD). Flow-weighted ortho-P concentration in the tile water was significantly lower with MD (0.09 mg L) compared with that of FD (0.15 mg L). Ortho-P loss in the tile water of this study was reduced with MD (36 g ha) by 80% compared with FD (180 g ha). Contrary to previous research, reduced ortho-P loss observed over the 4-yr study was not solely due to the reduced amount of water drained annually (63%) with MD compared with FD. During the spring period, when flow was similar between MD and FD, the concentration of ortho-P in the tile water generally was lower with MD compared with FD, which resulted in significantly less ortho-P loss with MD. We speculate that MDs ability to conserve water during the dry summer months increased corns uptake of water and P, which reduced the amount of P available for leaching loss in the subsequent springs.

Soil Organic Carbon and Nitrogen Fractions in Temperate Alley Cropping Systems

Abstract Alley cropping may promote greater sequestration of soil organic carbon. The objective of this study was to examine spatial variability of soil organic carbon (C) and nitrogen (N) fractions relative to tree rows in established alley cropping systems in north central Missouri. Soils were collected to a depth of 30 cm from two alley cropped sites, a 19‐yr‐old pecan (Carya illinoinensis)/bluegrass (Poa trivialis) intercrop (pecan site) and an 11‐yr‐old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (maple site). Particulate organic matter (POM) C constituted 15–65% and 14–41% of total organic C (TOC) at the pecan and maple sites respectively, whereas POM N comprised 3 to 24% of total N (TKN). TOC and TKN were on average 13% and 18% higher at the tree row than at the middle of the alley for surface soils (0–10 cm) at the pecan site, respectively. Similarly, POM C was two to three times higher at the tree row than the alley for subsurface soils at the maple site. No differences in microbial biomass C and N between positions were observed. Observed results suggest the existence of spatially dependent patterns for POM C, TOC, and TKN, relative to tree rows in alley cropping.