We evaluated the potential of prairie wetlands in North America as carbon sinks. Agricultural conversion has resulted in the average loss of 10.1 Mg ha À 1 of soil organic carbon on over 16 million ha of wetlands in this region. Wetland restoration has potential to sequester 378 Tg of organic carbon over a 10-year period. Wetlands can sequester over twice the organic carbon as no-till cropland on only about 17% of the total land area in the region. We estimate that wetland restoration has potential to offset 2.4% of the annual fossil CO 2 emission reported for North America in 1990. D

Little is known about the effects of root pruning by insects on nutrient content of maize (Zea maysL.). The objective of this study was to evaluate root damage effects caused by western corn rootworm (WCR, Diabrotica virgifera virgiferaLeConte) larval feeding on Fe, Na, K, Ca, Mg, and N contents in shoots and seeds of maize hybrid ‘Pioneer 3978’. The experimental design was a randomized complete block, and treatments included applications of 0, 1000, 2000,4000, and 8,000 WCR eggs per lineal meter of row in 1982 and 0,4000, and 12 000 WCR eggs per lineal meter of row in 1983. Maize seeds were planted ca. 23 cm apart in Brookings sicl (pachic Udic Haploborolls) soil. Aboveground plant samples were collected before intense larval feeding and after adult beetle emergence. These shoot samples and grain harvested at maturity were weighed and analyzed for their nutrient content. Severe root pruning decreased shoot dry weight and reduced grain yields at harvest by 13.5% in 1982 and by 9.7% in 1983. Contents of K, Mg, and Ca decreased and Fe and Na contents increased in shoots in 1982, but were not affected by root pruning in 1983. Accumulation of Na and Fe in shoots was attributed to compensatory branch root growth at critical stages of plant development. Root pruning may have caused new root development or branching into parts of the soil where Fe and Na could be obtained. Grain yield and grain Na content were related directly to the amount of root pruning in 1982. In 1983, grain yield was reduced and element content was altered by root pruning, but not in a simple linear manner. The results suggested that further studies of root pruning by WCR larvae of additional hybrids and their inbred parents may aid identification of elemental functions for maize.

No abstract

Measurement of soil organic carbon (OC) is slow and expensive when inorganic carbon (IC) is present. Our objective was to develop an automated volumetric IC analysis system, thus allowing OC to be determined by difference. The system was developed by combining a pressure transducer with a personal computer (PC), data acquisition board, and appropriately developed software. The volumetric system was compared with combustion, neutralization, and sum of Ca + Mg techniques for samples containing up to 60 g kg−1 IC. Correlations between methods showed linear agreement (r2 ≥ 0.994). The volumetric system was more precise for relatively low IC amounts (2.0 g kg−1) and could process 20 samples h−1.

The adsorption of soluble P by surface soil and suspended sediment material during transport in surface runoff under field and simulated laborato ry conditions was investigated. The soluble P concentration of surface runoff from several Southern Plains cropped and grassed watersheds decreased with an increase in sediment concentration. A linear inverse relationship between soluble P and sediment concentration was significant over a wide range in sediment concentration. The slope values of the relationship were similar for different watersheds on the same major soil type. Using soil from these watersheds in simulated surface runoff, sorption of soluble P added in rainfall was found to occur during transport. The magnitude of this sorption was more closely related to the sorptive capacity of the sediment in the surface runoff than to that of the surface soil material. The results suggest that for unfertilized watersheds and for watersheds where fertilizer P is incorporated into the surface soil, away from the zone of immediate removal in surface runoff, the leaching of P from the vegetative cover can contribute significant amounts of soluble P to runoff, and that soil material may act as a P sink rather than a P source.

Seven cropland watersheds and four rangeland watersheds in central Oklahoma were monitored for surface hydrology and discharge of nitrogen, phosphorus, and sediment over a 1 year period. Precipitation and runoff were much above normal during the study. Sediment losses from the continuously grazed rangeland watersheds ranged from 18 to 23 metric tons/ha during the study. None of the sediment losses from the other watersheds exceeded 10 metric tons/ha.Total nutrients discharged in runoff ranged from 2 to 15 kg/ha of N and 1 to 11.5 kg/ha of P. Flow‐weighted mean concentrations ranged from 1 to 6 ppm of total N, 0.2 to 1.9 ppm of nitrate‐N, 0.5 to 4.8 ppm of total P, and 0.04 to 0.9 ppm of soluble P. Runoff losses of soluble inorganic nitrogen were generally less than those quantities received in rainfall. Concentrations of soluble phosphorus in runoff from the cropland watersheds were much greater than from the rangeland watersheds. Losses of fertilizer nitrogen and phosphorus did not exceed 5% of the most recent applications, although surface runoff was 4‐ to 10‐fold greater than that observed in previous years.

Nitrogen and phosphorus discharges in runoff from nearly level cropland and 3% sloping rangeland were measured from July 1972, to June 1976. Sediment discharges and runoff amounts from these 5‐ to 18‐ha watersheds were measured from July 1966, to June 1976. Sediment and nutrient discharges varied greatly from year to year and between different land uses. We concluded that long records are needed to compare discharges from different management practices. The average and maximum annual sediment discharges, respectively, were 3,600 and 8,900 kg/ha from irrigated cotton (Gossypium hirsutum), 900 and 3,900 kg/ha from dryland wheat (Triticum aestivum), 400 and 1,800 kg/ha from range with limited grazing, and 9,000 and 23,000 kg/ha from overgrazed range. Maximum annual sediment discharges occurred during the period in which nutrient discharges were measured. Maximum annual nutrient discharges were 13 kg/ha total N, 4 kg/ha nitrate N, 11 kg/ha total P, and 2 kg/ha soluble P. The average annual discharge for each nutrient form and land use was about half of its maximum value. Nitrate accounted for 10 to 30% of the total N discharged. Soluble phosphate accounted for about 20% of the total P discharged from cropland, and <10% of that discharged from rangeland. Annual deposition in rainfall averaged 5 kg/ha N and 0.15 kg/ha P.

Herbicides transported to surface waters by agricultural runoff are partitioned between solution and solid phases. Conservation tillage that reduces upland erosion will also reduce transport of herbicides associated with the solid phase. However, transport of many herbicides occurs predominantly in solution. Conservation tillage practices may or may not reduce transport of solution-phase herbicides, as this depends on the runoff volume. Reducing herbicide application rate is another approach to minimize off-site transport. Herbicide banding can reduce herbicide application rates and costs by one-half or more. Our objective was to compare herbicide losses in runoff from different tillage practices and with band- or broadcast-applied herbicides. The herbicides alachlor [2-chloro-2',6'-diethyl-N-(methoxymethyl)acetanilide] and cyanazine [2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropionitrile] were broadcast- or band-applied to plots managed in a moldboard plow, chisel plow, or ridge till system. Herbicide concentration in runoff was largest for the first runoff event occurring after application and then decreased in subsequent events proportional to the cumulative rain since the herbicide application. When herbicides were broadcast-applied, losses of alachlor and cyanazine in runoff followed the order: moldboard plow > chisel plow > ridge till. Conservation tillage systems reduced runoff loss of herbicides by reducing runoff volume and not the herbicide concentration in runoff. Herbicide banding reduced the concentration and loss of herbicides in runoff compared with the broadcast application. Herbicide losses in the water phase averaged 88 and 97% of the total loss for alachlor and cyanazine, respectively. Cyanazine was more persistent than alachlor in the soil.