Water and nutrient flow were measured on a complex upland—peatland watershed in north central Minnesota. Annual water budgets for upland and peatland components and for the total watershed were developed. Nutrient input and output budgets were developed for each component on a seasonal basis, using net precipitation inputs, and an annual nutrient budget was developed for the entire watershed, using gross precipitation and total outputs. Both components evapotranspire water near potential rates. The upland converts 34% of the water input to water yield, while the peatland (a bog in a lower topographic position) converts 55% of its water input to water yield. The upland annually retains some N, P, K, and Ca from net precipitation, but passes through Mg and supplies Na in excess of inputs. The peatland is a nutrient trap retaining 36—60% of all nutrient inputs annually. There are striking differences in the seasonal retention of nutrient forms between the upland and bog. The total watershed accumulates P and (apparently) N but loses more K, Ca, Mg, and Na than it receives in gross precipitation. Nutrient flow is interpreted for the design of nutrient—added technologies (fertilization and sewage treatment) and as a bench mark for nutrient—depleted technology (whole—tree harvesting).
Nitrogen and phosphorus losses were determined in plant leachates from alfalfa, Kentucky bluegrass, barley straw stubble, and oats straw stubble. Plant samples harvested from the field were either leached immediately or were desiccated by drying or freezing before leaching. The extraction of soluble nitrogen and soluble phosphorus in leachates from aloealoea and bluegrass was greatly increased by drying or freezing. These same treatments, however, released only small amounts of soluble phosphorus from barley and oats straw. Estimated soluble nutrient losses indicate that leaching of alfalfa and bluegrass by surface runoff water could contribute substantial amounts of nitrogen and phosphorus to lakes and streams.The concentrations and amounts of the various nutrients in runoff from agricultural areas result from the interaction of many factors. These factors include type of crop, cultural and conservation practices, length and steepness of slope, amount and distribution of precipitation, soil infiltration and percolation characteristics, and size of contributing watershed. One factor, the leaching of crops and crop residues by precipitation and/or runoff, has not been thoroughly assessed, but under certain conditions may be an important source of nutrients in surface runoff.
Improved fertilizer N management with respect to placement and timing is especially important in high‐residue systems designed to improve N‐use efficiency and to speed adoption of erosion controlling tillage practices. By means of point‐injection technology, fertilizer solutions now can be applied and soil‐incorporated with minimal disturbance of surface residue or existing plants. This study was conducted in large non‐weighing lysimeters (with reconstituted soil horizons) to determine the recovery of 15N – labeled urea‐ammonium nitrate (UAN) solution by continuous no‐till corn (Zea mays L.) during the initial year of application and two subsequent years for four N management systems. The UAN solution was point‐injected in split applications at rates of 125 or 200 kg N ha−1, or knifed‐in or surface‐banded right after plant emergence at 200 kg N ha−1. For the initial year of 15N application, the percent recovery of labeled N (NR) in grain was 48, 39, 33, and 30% for point‐injected (low rate/split), point‐injected (high rate/split), knifed‐in, and surface‐banded, respectively. The percentage of total grain N derived from labeled N (Nf) ranged from 57 to 67% and was in the order of point‐injected (high rate/split) > knifedin > point‐injected (low rate/split) > surface‐banded. Residual labeled N recovery in grain ranged from 2.3 to 4.6% for the second season and from 0.9 to 1.0% for the third season with no significant differences among application treatments for either season. After five seasons the NR values for labeled N determined in the soil N pool still ranged from 20 to 26%. UAN solution applied in split applications with the point injector was used more efficiently by corn than when knifed‐in or surface‐banded in a single application, indicating the point‐injection/split application system is an option for improved N management in no‐till corn.
Fertilizer N utilization by corn (Zea mays L.) is influenced by different fertilizer management and tillage systems. A study was conducted in central Iowa during two consecutive years to evaluate the uptake and recovery of labeled N for continuous corn grown in two tillage systems with two fertilization methods. Tillage systems were fall moldboard‐plow and ridge‐till. Labeled N (5% 15N) as 28% urea‐ammonium nitrate solution (UAN) was either surface‐applied in the fall before any primary tillage or banded (knifed‐in) between rows at 224 kg N ha−1 just before planting. Depending on tillage and fertilization method, corn grain yields ranged from 1.3 to 7.3 Mg ha−1 which were below normal due to adverse weather conditions during the two growing seasons. The percent of plant N derived from labeled N (Nf) in the sixth leaf (50% silk) and in mature grain, stover, and whole plants was significantly lower for fall surfaceapplied 15N than for spring banded 15N. For mature whole plants, Nr ranged from 9 to 59% and averaged 53% for spring banded and 17% for fall surface‐applied 15N. Labeled N recovery by mature corn grain was affected by fertilization method and growing season and ranged from 1 to 25% during the 2‐yr period. Labeled N recovery by mature whole plants ranged from 2 to 41% and averaged four times greater for spring banded than for fall surface‐applied 15N. About 1 yr after application, an average of 20% of the 15N remained in the soil profile; and 95% of the residual 15N was found in the organic N pool. Compared with spring banded N, fall surface‐applied N was extremely inefficient for both tillage systems.
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