Presumably these expenses have benefits, otherwise companies wouldn't be using them? It's like saying a company saved $200k by dumping their computers... so they can do everything on paper.
Most agricultural chemical products are profitable in the way a loan is profitable. You get higher yields now, but you're disrupting the environment and making it more vulnerable to pests, drought and erosion in the long run. As these problems start to become apparent, your only solution to maintain yields is to use more and more products, until the land is so marginal it collapses.
Probably referring to dust bowl era land like Oklahoma. I don't like the word collapse, but I'm guessing there are implying that the ground is x% less productive for crop production or grazing).
The risk of land collapsing is probably greatest West of the Missouri river where historic rainfall is less and historic topsoil is less (Dakotas, Nebraska, Colorado, Kansas, etc).
Overuse of fertilizers can cause chemical burn which damages the soil ecology. In combination with tilling it will gradually destroy the soil quality.
Pesticides destroy insect diversity, including predatory insects that keep pests in check. This is particularly problematic because pest populations tend to recover more quickly than predator populations, so if you stop spraying the problem comes back worse. Pesticides can also harm bird and amphibian populations, which play a role in pest control.
Maybe not what they are referring too, but you can absolutely 'brick' land by over applying chemicals ('salting the earth'). There is a continuum depending on which chemical and how 'bricked' you make it.
Dave Montgomery posits that soil degradation has determined the lifespan of past civilizations. At the rate that plowing erodes soil it takes about 1000 years to deplete the resource to the point of desertification.
