Johannesburg — FORMER Springbok coach Carel du Plessis believes the world champions' ability to maintain their success in the lead-up to the 2011 Rugby World Cup will depend heavily on improving their depth.

Du Plessis said instead of relying on 15 first-choice players to carry the team -- which has been the case in the last two seasons -- the coaching staff had to make a concerted effort to increase the number of world- class players to about 24 to ensure that the reserve strength is at the same level as the other players.

Du Plessis' comments followed the Springboks' final Test of the year on Saturday against Ireland at Croke Park, in which they lost 15-10 .

The disappointment of the defeat -- which was their second in three Tests on their European tour -- was soothed somewhat as the team celebrated being crowned the International Rugby Board's Team of the Year shortly thereafter.

The award capped off a superb season which featured Tri-Nations and British and Irish Lions series victories.

It was the third time since 2004 that the team won the prestigious award -- they received the honours in 2004 and 2007 under Rugby World Cup-winning coach Jake White.

"Being crowned the IRB team of the year is something the Springbok players and management can be proud of," said Du Plessis. "They had a great year and it is pleasing that they received the recognition they deserved. But the challenge now is to maintain this success moving forward and this will require growing the reserve strength.

"Instead of having 15 players that we rely on all the time, we need to have 24 or 25 players who can step into the Test lineup on any given day. We need five or six quality locks and loose forwards and a quality player who could fill in for Fourie du Preez at scrumhalf.

"We played three Tests and lost two of them against very good teams on the day," he said. "But despite this, I don't think one should take anything away from what this group of players achieved this season.

"Our lineouts and discipline let us down against Ireland, but despite this we are a strong team all-round and most international teams will still see us as the team to beat."

Du Plessis suggested that the national coaches keep the door open to overseas-based Springboks -- especially after watching prop BJ Botha transform the Bok scrum into the machine it was in 2007 -- and said they should try to bring more variation into their game plan.

The high-pressure kick-and- chase game worked well against the British and Irish Lions and in the Tri- Nations, but it failed against Ireland, resulting in the team simply handing back possession to the home team.

"We must bring in an extra dimension by carrying the ball," said Du Plessis. "The top teams now want to do more counterattacking and some of them will keep the ball and starve us of possession. Our kick- and-chase game has delivered results, but we have to do more."