Potassium and Phosphorus Fertilizer Impacts on Alfalfa Taproot Carbon and Nitrogen Reserve Accumulation and Use During Fall Acclimation and Initial Growth in Spring.

Phosphorus (P) and potassium (K) impact alfalfa (Medicago sativa L.) performance, but how these nutrients alter taproot physiology during fall acclimation and subsequent growth in spring is unclear. Our objectives were to: (1) determine seasonal patterns for taproot P and K concentrations during fall acclimation and during initial shoot growth in spring; (2) determine how P and K nutrition impacts accumulation of taproot C and N reserves during fall and their subsequent use when shoot growth resumes in spring; and (3) assess how addition of P and K fertilizer impacts survival and shoot growth in spring. Two P (0 and 75 kg ha-1) and two K (0 and 400 kg ha-1) treatments were applied and taproots were sampled between September and December, and again from March to May over 2 years. Concentrations of taproot sugar, starch, buffer-soluble protein, amino-N, and RNA pools were determined. While P and K fertilizer application increased taproot P and K concentrations two- to three-fold, concentrations of P and K in taproots over time did not change markedly during cold acclimation in fall, however, taproot P declined in spring as plant growth resumed. Compared to the 0K-0P treatment, taproots of plants fertilized with 400K-75P had higher starch, protein, amino-N, and RNA, but reduced sugar concentrations in fall. Concentrations of all these pools, except starch, declined during the initial 2 weeks of sampling beginning in late March as shoot growth resumed in spring. Herbage yield in May was highest for the 400K-75P treatment and least for the 0K-0P treatment, differences that were associated with variation in mass shoot-1 and not shoots m-2. High yield of the 400K-75P plants in May was consistently associated with greater concentrations and use of amino-N, soluble protein, and RNA pools in taproots, and not with accumulation and use of starch and sugar pools. Understanding factors leading to the accumulation of taproot N reserves and RNA during cold acclimation in fall and their use during the initial growth in spring should enhance efforts to improve alfalfa growth and herbage yield in spring.

Development of phosphorus sorption capacity-based environmental indices for tile-drained systems.

The persistent environmental relevance of phosphorus (P) and P sorption capacity (PSC) on P loss to surface waters has led to proposals for its inclusion in soil fertility and environmental management programs. As fertility and environmental management decisions are made on a routine basis, the use of laborious P sorption isotherms to quantify PSC is not feasible. Alternatively, pedotransfer functions (pedoTFs) estimate PSC from routinely assessed soil chemical properties. Our objective was to examine the possibility of developing a suitable pedoTF for estimating PSC and to evaluate subsequent PSC-based indices (P saturation ratio [PSR] and soil P storage capacity [SPSC]) using data from an in-field laboratory where tile drain effluent is monitored daily. Phosphorus sorption capacity was well predicted by a pedoTF derived from soil aluminum and organic matter (R² = .60). Segmented-line relationships between PSR and soluble P were observed in both desorption assays (R² = .69) and drainflows (R² = .66) with apparent PSR thresholds in close agreement at 0.21 and 0.24, respectively. Negative SPSC values exhibited linear relationships with increasing soluble P concentrations in both desorption assays and drainflows (R² = .52 and R2  = .53 respectively), whereas positive SPSC values were associated with low SP concentrations. Therefore, PSC-based indices determined using pedoTFs could estimate the potential for subsurface soluble P losses. Also, we determined that both index thresholds coincided with the critical soil-test P level for agronomic P sufficiency (22 mg kg-1 Mehlich-3 P) suggesting that the agronomic threshold could serve as an environmental P threshold.

Phosphorus and potassium effects on taproot C and N reserve pools and long-term persistence of alfalfa (Medicago sativa L.).

Improved P and K nutrition can enhance yield and persistence of alfalfa (Medicago sativa L.) grown on low fertility soils, but it is unknown if the improved agronomic performance is associated with greater taproot N and C reserves. Our objective was to use cluster analysis to determine how alfalfa plant persistence is altered by P and K fertilization, and determine if changes in specific taproot C and/or N reserves were associated with alfalfa plant death. Taproots were dug and plants counted in May and December of each year and taproots analyzed for P, K, starch, sugar, amino-N, and soluble protein. K-means clustering was used to create six clusters that were subsequently compared using two-sample t-tests. Low K in herbage and taproots was associated with low yield and poor persistence of the Low and Very Low clusters and taproots of these plants generally had low starch, protein, and amino-N concentrations. Plants died primarily between May and December. Plant persistence of the low yielding, P-deficient Medium cluster was high and associated with high starch concentrations. Low amino-N concentrations in taproots may provide an early indication of potential plant death because these were evident in poor-persisting Low and Very Low clusters early in the study.

Nitrogen Reserve Pools in Two Miscanthus × giganteus Genotypes under Contrasting N Managements.

Nitrogen (N) reserves in vegetative tissues contribute N to regrowth of Miscanthus × giganteus shoots in spring, but our understanding of how N fertilization and plant genotype affect this process is incomplete. Our specific objectives were to: (1) determine how N fertilizer management impacts accumulation of dry matter and N among aboveground and belowground tissues and organs; (2) understand how changes in N management and tissue N concentration influence seasonal fluctuations in concentrations of buffer-soluble proteins and amino acids in putative storage organs including rhizomes and roots; and (3) characterize genotypic variability and genotype × N interactions for N reserve accumulation and use among Miscanthus × giganteus genotypes. Established plots of the IL Clone and Nagara-sib population were fertilized with 0-0, 0-150, 75-75, 150-0, and 150-150 kg N ha-1 where the first numeral denotes the N rate applied in 2011 (Year 1) and the second number denotes the N rate applied in 2012 (Year 2). Rhizomes, roots, stembases, and shoots were sampled at 6-week intervals between March and August and then in November at dormancy. Concentrations of N, soluble protein and amino-N increased in all tissues with fertilizer N application. With the exception of rhizome amino-N, concentrations of these N pools in roots and rhizomes declined as plants resumed growth in spring and increased sharply between August and November as growth slowed. Losses in shoot and stembase N mass between August and November were similar to total N accumulation in roots and rhizomes during this interval. Compared to the unfertilized control, specific N managements enhanced growth of above- and belowground tissues. The IL Clone generally had greater biomass yield of all organs than the Nagara-sib; the exception being shoot biomass in November when extensive leaf senescence reduce yield of the IL Clone. High biomass yields were obtained with 75 kg N ha-1 applied annually rather than semi-annual N applications of 150 kg N-1 ha that depended on N recycling from roots/rhizomes as a supplemental N source.

Evaluation of simulated strategies for reducing nitrate-nitrogen losses through subsurface drainage systems.

The nitrates (NO(3)-N) lost through subsurface drainage in the Midwest often exceed concentrations that cause deleterious effects on the receiving streams and lead to hypoxic conditions in the northern Gulf of Mexico. The use of drainage and water quality models along with observed data analysis may provide new insight into the water and nutrient balance in drained agricultural lands and enable evaluation of appropriate measures for reducing NO(3)-N losses. DRAINMOD-NII, a carbon (C) and nitrogen (N) simulation model, was field tested for the high organic matter Drummer soil in Indiana and used to predict the effects of fertilizer application rate and drainage water management (DWM) on NO-N losses through subsurface drainage. The model was calibrated and validated for continuous corn (Zea mays L.) (CC) and corn-soybean [Glycine max (L.) Merr.] (CS) rotation treatments separately using 7 yr of drain flow and NO(3)-N concentration data. Among the treatments, the Nash-Sutcliffe efficiency of the monthly NO(3)-N loss predictions ranged from 0.30 to 0.86, and the percent error varied from -19 to 9%. The medians of the observed and predicted monthly NO(3)-N losses were not significantly different. When the fertilizer application rate was reduced ~20%, the predicted NO(3)-N losses in drain flow from the CC treatments was reduced 17% (95% confidence interval [CI], 11-25), while losses from the CS treatment were reduced by 10% (95% CI, 1-15). With DWM, the predicted average annual drain flow was reduced by about 56% (95% CI, 49-67), while the average annual NO(3)-N losses through drain flow were reduced by about 46% (95% CI, 32-57) for both tested crop rotations. However, the simulated NO(3)-N losses in surface runoff increased by about 3 to 4 kg ha(-1) with DWM. For the simulated conditions at the study site, implementing DWM along with reduced fertilizer application rates would be the best strategy to achieve the highest NO(3)-N loss reductions to surface water. The suggested best strategies would reduce the NO(3)-N losses to surface water by 38% (95% CI, 29-46) for the CC treatments and by 32% (95% CI, 23-40) for the CS treatments.

Nitrate, phosphate, and ammonium loads at subsurface drains: agroecosystems and nitrogen management.

Artificial subsurface drainage in cropland creates pathways for nutrient movement into surface water; quantification of the relative impacts of common and theoretically improved management systems on these nutrient losses remains incomplete. This study was conducted to assess diverse management effects on long-term patterns (1998-2006) of NO, NH, and PO loads (). We monitored water flow and nutrient concentrations at subsurface drains in lysimeter plots planted to continuous corn ( L.) (CC), both phases of corn-soybean [ (L.) Merr.] rotations (corn, CS; soybean, SC), and restored prairie grass (PG). Corn plots were fertilized with preplant or sidedress urea-NHNO (UAN) or liquid swine manure injected in the fall (FM) or spring (SM). Restored PG reduced NO eightfold compared with fields receiving UAN (2.5 vs. 19.9 kg N ha yr; < 0.001), yet varying UAN application rates and timings did not affect NO across all CCUANs and CSUANs. The NO from CCFM (33.3 kg N ha yr) were substantially higher than for all other cropped fields including CCSM (average 19.8 kg N ha yr, < 0.001). With respect to NH and PO, only manured soils recorded high but episodic losses in certain years. Compared with the average of all other treatments, CCSM increased NH in the spring of 1999 (217 vs. 680 g N ha yr), while CCFM raised PO in the winter of 2005 (23 vs. 441 g P ha yr). Our results demonstrate that fall manuring increased nutrient losses in subsurface-drained cropland, and hence this practice should be redesigned for improvement or discouraged.

Dissolved organic carbon losses from tile drained agroecosystems.

Artificial subsurface drainage is commonly used in midwestern agriculture and drainage losses of dissolved organic carbon (DOC) from such systems are an under-quantified portion of the terrestrial carbon (C) cycle. The objectives of this study were to determine the effect of common agricultural management practices on DOC losses from subsurface tile drains and to assess patterns of loss as a function of year, time of year, and drainflow. Daily drainflow was collected across six water years (1999-2004) from a restored prairie grass system and cropping systems which include continuous corn (Zea mays L.) and corn-soybean [Glycine max (L.) Merr.] rotations fertilized with urea-ammonium-nitrate (UAN) or swine (Sus scrofa) manure lagoon effluent. The DOC concentrations in tile drainflow were low, typically <2 mg L(-1). Yearly DOC losses, which ranged from 1.78 to 8.61 kg ha(-1), were not affected by management practices and were small compared to organic C inputs. Spring application of lagoon effluent increased yearly flow-weighted (FW)-DOC concentrations relative to other cropping systems in three of the years and increased monthly FW-DOC concentrations when drainflow occurred within 1 mo of application. Drainflow was significantly and positively correlated with DOC loss. Drainflow also affected DOC concentrations as greater 6-yr cumulative drainflow was associated with lower 6-yr FW-DOC concentrations and greater daily drainflow was associated with higher daily DOC concentrations. Our results indicate that lagoon effluent application and fertilizer N rates do not affect long-term losses of DOC from tile drains and that drainflow is the main driver of DOC losses.

Greenhouse gas fluxes in an eastern Corn Belt soil: weather, nitrogen source, and rotation.

Relative contributions of diverse, managed ecosystems to greenhouse gases are not completely documented. This study was conducted to estimate soil surface fluxes of carbon dioxide (CO(2)), methane (CH(4)), and nitrous oxide (N(2)O) as affected by management practices and weather. Gas fluxes were measured by vented, static chambers in Drummer and Raub soil series during two growing seasons. Treatments evaluated were corn cropped continuously (CC) or in rotation with soybean (CS) and fertilized with in-season urea-ammonium nitrate (UAN) or liquid swine manure applied in the spring (SM) or fall (FM). Soybean (SC) rotated with CS and restored prairie grass (PG) were also included. The CO(2) fluxes correlated (P 8 kg ha(-1) yr(-1) in CCSM; differences were driven by pulse emissions after N fertilization in concurrence with major rainfall events. These results suggest fall manure application, corn-soybean rotation, and restoration of prairies may diminish N(2)O emissions and hence contribute to global warming mitigation.

Impact of climate change on crop nutrient and water use efficiencies.

Implicit in discussions of plant nutrition and climate change is the assumption that we know what to do relative to nutrient management here and now but that these strategies might not apply in a changed climate. We review existing knowledge on interactive influences of atmospheric carbon dioxide concentration, temperature and soil moisture on plant growth, development and yield as well as on plant water use efficiency (WUE) and physiological and uptake efficiencies of soil-immobile nutrients. Elevated atmospheric CO(2) will increase leaf and canopy photosynthesis, especially in C3 plants, with minor changes in dark respiration. Additional CO(2) will increase biomass without marked alteration in dry matter partitioning, reduce transpiration of most plants and improve WUE. However, spatiotemporal variation in these attributes will impact agronomic performance and crop water use in a site-specific manner. Nutrient acquisition is closely associated with overall biomass and strongly influenced by root surface area. When climate change alters soil factors to restrict root growth, nutrient stress will occur. Plant size may also change but nutrient concentration will remain relatively unchanged; therefore, nutrient removal will scale with growth. Changes in regional nutrient requirements will be most remarkable where we alter cropping systems to accommodate shifts in ecozones or alter farming systems to capture new uses from existing systems. For regions and systems where we currently do an adequate job managing nutrients, we stand a good chance of continued optimization under a changed climate. If we can and should do better, climate change will not help us.

Potassium fertilization effects on isoflavone concentrations in soybean [Glycine max (L.) Merr.].

Soybean isoflavone concentrations vary widely, but the contribution of soil fertility and nutrient management to this variability is unknown. Field experiments from 1998 to 2000 on soils with low to high exchangeable potassium (K) concentrations evaluated K application and placement effects on isoflavone concentrations and composition of soybean in various tillage and row-width systems. Soybean seed yield and concentrations of daidzein, genistein, glycitein, leaf K, and seed K were measured. Significant increases in daidzein, genistein, and total isoflavone were observed with direct deep-banded K or residual surface-applied K on low-K soils. Positive effects of K fertilization on isoflavones were less frequent on medium- to high-testing K soils. Both individual and total isoflavones were often positively correlated with seed yield, leaf K, and seed K on low-K soils. Appropriate K management could be an effective approach to increase isoflavone concentrations for soybeans produced on low- to medium-K soils.