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Best Practices For Manure Management


As fall has arrived and the time to empty manure  pits  in  preparation  for winter storage is nearly upon us, there’s no better time to think about manure management strategies. Research has demonstrated that there is a greater risk for phosphorus  (P) and nitrogen (N) loss when manure is applied to fields in the fall rather than the spring. Therefore, while time can be short during the fall harvest season, it’s especially important to follow best practices.

This is particularly true in the Northeast  where  more   than   half   of annual precipitation can occur during the nongrowing season. This precipitation, combined with limited water uptake by plants, low rates of evaporation, and extended periods of frozen soils, leads to a higher rate of both surface runoff and tile drainage during fall, winter, and early spring. Research at Miner Institute has found that   approximately    three-quarters of annual runoff occurs between November 1 and April 30.  Not  only is the risk of runoff greater, but there will be a long delay between when the manure is applied and plants will once again require those nutrients.

Cover crops can help bridge this gap by sequestering fall-applied nutrients during the nongrowing season, but another key to nutrient retention is incorporating the manure  into  the soil. This can significantly reduce N volatilization losses to the atmosphere. Perhaps more importantly, greater manure-soil contact increases the amount of P bound to the soil, resulting in a lower risk of transport  in subsequent runoff (especially as dissolved, bioavailable P). This can be accomplished by injecting the manure, but in the absence of manure injection equipment, tilling in a broadcast manure application can achieve the same objective.

A recent two-year study in Wisconsin found additional benefits from tillage following late fall/early winter applications of liquid dairy manure. Research plots were managed  either as no-till or fall chisel plowed with a spring soil finisher. The researchers surface-applied manure (4,000 gal/A) to the plots following fall corn harvest for silage and then either incorporated the manure with a  chisel  plow  or  left it on the surface. The study also looked at how the timing of manure applications impacted nutrient losses (no manure, December, or January applications).

Regardless of the timing of the manure application, the tilled plots experienced fewer  surface  runoff   events   and less total surface runoff than  plots  that didn’t receive tillage. This may sound somewhat counterintuitive, as one benefit of no-till can be greater infiltration rates due to a more extensive network of macropores.  However,  the ground was frozen for significant periods during the nongrowing season, reducing much of the impact that differences in soil structure between treatments may have imparted.

The decrease in surface runoff from the tilled plots had a significant impact on the level of nutrient export relative to the no-till plots. The no-till plots lost 200 times more P in the first year and a more moderate 3.4 times more  P in the second year compared to the tilled plots. Additionally, they found that early or late winter applications mattered less than whether the soil was frozen at the time of application. Applying manure to frozen soils, regardless of tillage treatment, resulted in greater nutrient loss because the manure had no opportunity to infiltrate and interact with the soil.

The researchers attributed the reductions in surface runoff and P loss to the much greater surface roughness in the tilled plots compared to the relatively smooth surface in the no-till plots. This can be especially important during the winter months, when a frost layer in the surface soils prevents water from immediately infiltrating the soil and increases the risk of surface runoff events. Due  to the surface roughness in the tilled plots, there was greater opportunity for water to pond and ultimately infiltrate  the  soil or evaporate, rather than leaving as runoff. In contrast, there was minimal opportunity for surface ponding in the no-till plots, leading to much more immediate runoff down the plot slope (5.8% slope). The drastic reduction  in P loss during the first year in the tilled plots occurred because there was only one runoff event, as opposed to nine events in the no-till plots.

The results of this study reinforce the need to incorporate surface-applied manure to decrease the risk of offsite P transport. For those who work in a no- till system, it’s an important reminder that leaving manure on the field surface poses a significant risk for nutrient loss. Investigate the different methods of manure injection that will increase the manure-soil interactions to help minimize nutrient losses from the field, while maintaining the soil health benefits of your no-till system.

− Laura Klaiber klaiber@whminer.com

Source: WH Miner Institute


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