The National Assembly also justified the N14.5 billion increase in its budget, saying the lawmakers even slashed their budget compared to 2015.
Buhari signed the appropriation bill on Wednesday, June 20, as he lamented the changes the National Assembly made to the original budget proposals.
The President had tendered an N8.6 trillion 2018 budget before a joint session of the national assembly on November 7, 2017.
However, after lawmakers were done with the budget, the appropriation bill had been increased to the tune of N508billion and the national assembly budget had been increased to N139billion (from N125billion in the 2017 budget).
The lawmakers also slashed the capital expenditure estimates before the document was transmitted to the president for assent.
"The national assembly made cuts amounting to N347 billion in the allocations to 4,700 projects submitted to them for consideration and introduced 6,403 projects of their own amounting to N578 billion. Many of the projects cut are critical and may be difficult, if not impossible, to implement with the reduced allocation. Some of the new projects inserted by the national assembly have not been properly conceptualized, designed and costed and will, therefore, be difficult to execute," Buhari said during the budget signing at the Presidential Villa, Abuja.
He disclosed that he would send a supplementary budget.
The House of Representatives, however, said the alterations made to the 2018 budget were justifiable.
In a statement released on Wednesday, the spokesman for the lower legislative chamber, AbdulRazak Namdas, said the National Assembly "has a job to do".
He also blamed the delay in the implementation of the January-to-December budget cycle on heads of ministries, department and agencies (MDAs).
He said, "The house of representatives is appreciative of President Muhammadu Buhari in signing the 2018 Appropriation Bill into law and wish to make the following observations.
"That the budget is usually a proposal by the executive to the national assembly, which the latter is given the constitutional power of appropriation to alter, make additions, costs or reduce as it may deem necessary. The Legislature is not expected to be a rubber-stamp by simply approving the Executive proposals and returning the budget to Mr. President. Therefore, the additions Mr. President complained of in his speech are justifiable.
"We are on the same page with Mr. President in his desire to return our budget cycle to January-December. By the provisions of the Fiscal Responsibility Act, 2007, the budget estimates should be with the national assembly around September of the year. In the case of the 2018 budget, the estimates came behind schedule in November 2017, even though this attempt was seen as one of the earliest in recent years. Going forward, we urge the executive to speed up the reporting time to the National Assembly by complying fully with the FRA.
"Besides, there were delays that should be blamed on the heads of MDAs. Mr. President will recall that he had to direct ministers and heads of agencies to go to the National Assembly to defend their proposals. This came after the National Assembly had persistently raised the alarm over the non-cooperative attitudes of these government officials. On this grounds, the delay in passing the budget cannot be blamed on the legislature.
"New projects in budget. On this aspect, we have to remind Mr. President that we are representatives of our people and wish to state that even the common man deserves a mention in the budget by including projects that will directly affect his life positively. Some of the projects designed by the executive, as high-sounding as their names suggest, do not meet the needs of the common man."
Namdas also justified the N14.5 billion increase in the budget of the national assembly, saying the lawmakers slashed their budget compared to 2015.
"Before 2015, the budget of the national assembly was N150 billion for several years. It was cut down to N120bn in 2015 and further down to N115bn in 2016. In 2017, the budget was N125bn and N139.5bn in 2018. This means that the budget of the national assembly is still far below the N150bn in the years before 2015.
"While we commend Mr. President for a good working relationship, we also wish to state that we have a job to do, which requires adequate funding as well. The additional costs and projects to the budget were done in good faith for the sole purpose of improving the lives of Nigerians", the spokesman said.
He added that the National Assembly will welcome Buhari's proposal to forward a supplementary budget to it in order to look into the other grey areas of pressing demands.