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Mycorrhizal fungi colonize many terrestrial plants and often result in an increased uptake of P and several micronutrients. Little information is available on the relationships among vesicular-arbuscular endomycorrhizae (YAM), aquatic plants, and plant P concentrations. The major objectives of this study were to measure the degree of YAM colonization of wetland plants, and to determine the relationship between colonization and plant P concentrations when sampled from two contrasting water regimes (hydric soil with no surface water and hydric soil with a minimum of 10 cm of surface water). Two semipermanent wetlands in Lake County, South Dakota, were chosen for the study. Water regime did not have a significant effect on total or organic soil P concentration. Vesicular-arbuscular endomycorrhizal spore samples collected from wet soils averaged 5000 spores kg"' compared with 2740 spores kg"' in dry soils. The eight plant species evaluated to determine VAM colonization were reed canarygrass (Phalaris arundinacea L.), slough sedge (Carex atherodes Spreng.), river bulrush [Scirpus fluviatilis (Torr.) Gray], slender rush (Juncus tenuis Willd.), dogbane (Apocynum cannabinum L.), water smartweed (Polygonum amphibium L.), cattail (Typha Xglauca Godr.), and wild licorice (Glycyrrhiza lepidota (Nutt.) Pursh). Vescular-arbuscular endomycorrhizal colonization ranged from 78% (wild licorice) to none (slough sedge and slender rush). Roots from dry areas averaged 27% colonization compared with less than 1% in wet areas. Colonization levels of dogbane and reed canarygrass in dry zones were highly correlated to plant P concentrations. The results of this study indicate that several wetland plant species develop substantial mycorrhizal associations, particularly in relatively dry environments.

We compared the agronomic, economic, and ecological performance of alternative (organic), conventional, and reduced-till farming systems over a 7-year period. We evaluated the sustainability of the various systems regarding several concerns, including soil erosion, pollution potential, whole-farm productivity, energy use, environmental stress, economic performance, and farm size. The alternative systems relied primarily on forage legumes (alfalfa or clover) as substitutes for the pesticides and commercial fertilizers used in the other systems.Two studies were established in northeastern South Dakota in 1985. Study I emphasized row crops, Study II small grains. The alternative system in Study I, which included alfalfa hay in the rotation, was the most productive, both agronomically and economically. In Study II, the alternative system included a green manure crop (clover) in the 4-year rotation and had the lowest agronomic production; however, its economic performance was similar to the conventional system's. Year-to-year variability in production was lowest in the alternative systems. The alternative systems in both studies were the most energy-efficient, and the reduced-till systems the least. Judged by the distribution ofnitrate-N in the soil profile, the potential for groundwater pollution was higher in the conventional and reduced-till systems in Study I than in the alternative system. The alternative systems in both studies depended less on government payments for their profitability. Results in Study I also showed that more widespread adoption of alternative systems would tend to halt or slow the trend of ever-increasing farm size. These studies suggest that alternative systems are more sustainable in this agro-climatic area.

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On highly fertile soils, increases in plant growth resulting from starter fertilizers, applications generally do not occur unless root growth is restricted or temperatures are cool. The use of some conservation‐tillage systems may result in restricted root growth and cooler soils at planting. The purpose of this 3‐yr field study was to determine if growth and yield of soybeans [Glycine max (L.) Merr.] planted in a conservation‐tillage system would be increased by starter fertilizers, and if interactions occurred between residual fertility levels and starter fertilizers. Treatments included residual fertility levels (low P and K, low P and high K, high P and low K, and high P and K) and starter fertilizers (no starter, N, P, K, N‐P, N‐K, and N‐P‐K). The N, P, and K starter fertilizer rates were 16, 19, and 44 kg ha−1, respectively. Raising both residual P and K to the high soil test rating improved soybean yields 43%. The N‐containing starter fertilizers, especially those also containing P, increased early season plant root and top weights, but the K starters did not. However, the P, K, N‐K, and P‐K starter fertilizers had the greatest effect on yields; when compared to the control, they increased yields 46% when residual P, K, or both were low, and 26% when the residual P and K were high. The N, N‐P, and N‐P‐K starter fertilizers increased yields 21% when residual P was low, but had no effect on yields when P was high. Seed quality did not vary among residual fertility levels, but was improved by the starter fertilizers, especially those containing K. The P and K concentrations in the leaves just prior to pod set corresponded to differences in yields among residual fertility levels, but not to differences among starter fertilizers.

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