Organic sales grew 3%.
And recall that we communicated to you in May that customers bought approximately $20 million of product in the fourth quarter of fiscal 2020 due to pre-buying in our construction end markets and favorable weather conditions in our agricultural end market.
Absent this dynamic, first quarter organic sales would have increased 8% and non-residential would have been flat year-over-year.
We had another strong quarter in the domestic agriculture business, where sales grew 36%.
International net sales decreased 9% in the quarter.
As you can see on the chart on the screen, our residential end market exposure has increased to 38% of domestic sales, our second largest domestic end market behind non-residential.
Organic adjusted EBITDA margin increased 830 basis points, driven by favorable material costs, lower manufacturing and transportation costs driven by our operational initiatives, contributions from the proactive cost mitigation steps announced in March and leverage from the growth in pipe and allied products.
We've had roughly 80% of the salaried workforce, including sales, pretty much working from home since late March.
Net sales increased 23%, with 3% organic growth plus the contribution of Infiltrator.
Within ADS, domestic sales increased 4%, driven by sales growth in both the agriculture and construction end markets.
Importantly, sales increased 4% in both pipes and allied products.
From a profitability standpoint, our adjusted EBITDA increased $79 million, or 99% compared to the prior year.
Our organic adjusted EBITDA increased $38 million, with strong performance from our sales, operations, procurement and distribution teams.
Infiltrator contributed an additional $42 million to adjusted EBITDA and has many of the same benefits as ADS in this market environment.
We more than doubled our free cash flow in the quarter, increasing from $53 million in the first quarter of fiscal 2020 to $124 million in fiscal 2021.
Our working capital as a percent of sales decreased to about 21% as compared to about 25% last year.
Our trailing 12-month pro forma leverage ratio is now 1.9 times below our target range of 2 times to 3 times levered we've previously communicated and well ahead of our original target to achieve a leverage ratio of less than 3 times by the end of this calendar year.
We ended the quarter in a very favorable liquidity position, with $235 million in cash on June 30, 2020 and $289 million available under our revolving credit facility, bringing our total liquidity to $524 million.
Further, we paid down the remaining $50 million balance on our revolving credit facility this past Friday, bringing that balance to zero as of today.
Lastly, due to the uncertain market environment, we are not providing guidance on the call today.

Summary:
Lastly, due to the uncertain market environment, we are not providing guidance on the call today.