Cover crops, although they may reduce the leaching of NO3‐N to groundwater, may increase nutrient concentration in runoff because of biomass leaching during rainfall events. A simulated rainfall study was conducted in the laboratory to determine the effects of freezing alone and freezing plus drying treatments, loading rate, and rainfall intensity on the leaching of NH4‐N, NO3‐N, and inorganic P from the biomass of red clover (Trifolium pratense L.), annual ryegrass (Lolium multiflorum L.), and oilseed radish [Raphanus sativus (L.) var. oleifera Dc Metzg]. Concentration of P increased during early stages of leaching, then decreased slowly but remained greater than 50% of the maximum, even after the equivalent of 6.0 cm of simulated rainfall. Concentrations of NO3‐N were similar to P but changed less during leaching. Weighted mean concentrations of P ranged from less than 2.0 to more than 15 mg L−1. Concentrations were greatest with oilseed radish and least with red clover. Drying the sample in addition to freezing increased the P concentration, particularly in the initial leaching. About 30% of the biomass P was leached from oilseed radish and annual ryegrass, but only about 20% from red clover. Because oilseed radish had a greater biomass P concentration, the total P leached was much greater than for the other two species. Between 5 and 9% of the biomass N was leached as either NO3‐N or NH4‐N from ryegrass and red clover while over 10% was leached from oilseed radish. The results indicate that cover crop species differed markedly in their potential impact on nutrient concentration, particularly P, in runoff. Of the three cover crops tested, oilseed radish has the greatest potential impact and red clover the least.

Phosphorus (P) loss from agricultural land in surface runoff can contribute to eutrophication of surface water. This study was conducted to evaluate a range of environmental and agronomic soil P tests as indicators of potential soil surface runoff dissolved reactive P (DRP) losses from Ontario soils. The soil samples (0- to 20-cm depth) were collected from six soil series in Ontario, with 10 sites each to provide a wide range of soil test P (STP) values. Rainfall simulation studies were conducted following the USEPA National P Research Project protocol. The average DRP concentration (DRP30) in runoff water collected over 30 min after the start of runoff increased (p < 0.001) in either a linear or curvilinear manner with increases in levels of various STPs and estimates of degree of soil P saturation (DPS). Among the 16 measurements of STPs and DPSs assessed, DPS(M3) 2 (Mehlich-3 P/[Mehlich-3 Al + Fe]) (r2 = 0.90), DPS(M3)-3 (Mehlich-3 P/Mehlich-3 Al) (r2 = 0.89), and water-extractable P (WEP) (r2 = 0.89) had the strongest overall relationship with runoff DRP30 across all six soil series. The DPS(M3)-2 and DPS(M3)-3 were equally accurate in predicting runoff DRP30 loss. However, DPS(M3)-3 was preferred as its prediction of DRP30 was soil pH insensitive and simpler in analytical procedure, ifa DPS approach is adopted.

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Projected global demand for small grain cereals emphasizes the need for sustainable intensi cation with higher crop yields. Field studies on so red winter wheat (Triticum aestivum L.) examined interactions among three fertilizer N rates, eight fungicide application strategies, and various cultivars grown in nine eld environments in Ontario, Canada. A synergistic response occurred when a high rate of N was applied with a fungicide strategy that controlled disease. Overall, compared to a typical N rate of 100 kg ha -1 and no fungicide, yields increased by an average of 1.45 Mg ha -1 when N was applied at 170 kg ha -1 with the most intensive fungicide treatment pooled across sites. is yield response varied from 0.80 to 2.11 Mg ha -1 depending on eld site and pooled across cultivars. Fungicide strategies that included a T2 ( ag leaf timing) or T3 (anthesis timing) produced the highest yields across environments, especially at the high N rate and in most cultivars. e crop response to fungicide depended on the susceptibility of the cultivar to foliar disease and whether the eld environment was favorable for disease development. High N rates increased spike numbers and kernels spike -1 , whereas fungicides mainly increased kernel weight and kernels spike -1 . Prior to an economic analysis, results from this study indicates clear potential for increasing wheat performance by intensifying management with increasing N and deploying fungicide application strategies, especially in some cultivars and in high yielding environments that may be favorable for disease development.

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