I am trying to populate a column with the date that is the first of the month before a given date

i.e. If the date in column one is 25/01/2017, I want the date in column two to read 01/12/2016

So far, I have managed to take a month off, or reset it to the first of the month, but I can't work out a way to combine the two. Is it possible, or do I have to do it in two different statements. Here is what I have so far: 

```
 SELECT 
    PAY_START_DATE,
    DATEADD(MONTH, -1, CONVERT(DATE,PAY_START_DATE)) AS AMMENDONE,
    DATEADD(m, DATEDIFF(m, 0, PAY_START_DATE), 0) AS AMMENDTWO
FROM [hronline_iTrent].[iTrent].[Payroll]

```

And this gives the output: 

```
PAY_START_DATE | AMMENDONE | AMMENDTWO
2016-04-06     |06/03/2016 | 01/04/2016 00:00
2016-06-12     |12/05/2016 | 01/06/2016 00:00

```

Any chance I can combine the two so I can get an output like: 

```
PAY_START_DATE | AMMEND
2016-04-06     | 2016-03-01
2016-06-12     | 2016-05-01

```

(The format of the output is not important)