Tillage and reduced-input rotations affect runoff from agricultural fields

Seed Daily via SPX: No-till management practices can reduce soil erosion, but evidence suggests they can also lead to increased runoff of dissolved phosphorus from soil surfaces. Meanwhile, farmers looking to avoid herbicides often have to combat weeds with tillage, which causes erosion. With all of the tradeoffs of different management systems, which one should growers use? To answer that question, researchers from the USDA Agricultural Research Service compared nutrient and sediment loss from no-till, conventional tillage, and reduced-input rotation watersheds in a study published online in Soil Science Society of America Journal.

By keeping a protective layer of plant matter on the soil surface, no-till practices reduce the loss of soil and phosphorus (P) attached to soil particles. But no-till requires herbicides to control weeds, and even after adoption of the practice by many farmers, harmful algal blooms were still occurring in surface waters. It looked as if no-till, while decreasing particulate P loss, was leading to increased runoff of dissolved P.

"Normally when you apply P-containing fertilizers, you would incorporate them into the soil," says Martin Shipitalo, lead author of the study. "With no-till, you're just broadcasting it on the soil surface, leading to high P concentrations at the surface. Even if you get less particulate loss, runoff will pick up that dissolved P that's highly concentrated at the soil surface."

Shipitalo and his team decided to look at data from a 16-year experiment to compare soil and nutrient runoff in watersheds managed in three different ways - no-till, conventional tillage (chisel-till), and reduced-input rotations. "The idea with the reduced-input rotation was to have a conservation practice that worked for farmers who do not want to use herbicides or large amounts of mineral fertilizers," explains Shipitalo.

In the current study, researchers provided most of the nutrients to crops in the reduced-input watersheds by planting red clover and spreading manure instead of fertilizers. They minimized the amount of bare soils and used just a shallow disking instead of total inversion tillage to leave some crop residue on the soil surface. While herbicides were used in the experiment, they aren't necessary because the light tilling and in-row cultivation that was done kept weeds under control.

"Reduced-input rotations strike a medium between conventional tillage and no-till," says Shipitalo. "And they could easily be adapted to be organic rotations."...

Ferdynand Rusczcyc's 1898 painting, "The Soil"