The goal of sustainable intensification is to increase food production from existing farmland says the article in the journal’s Policy Forum by lead authors Dr Tara Garnett and Professor Charles Godfray from the University of Oxford. They say this would minimize the pressure on the environment in a world in which land, water, and energy are in short supply, highlighting that the environment is often over-exploited and used unsustainably.

Sustainable Intensification Will Change Agricultural Practice World Wide - Exposing The Truth

The authors, university researchers and policy-makers from NGOs and the UN, outline a new, more sophisticated account of how ‘sustainable intensification’ should work. They recognise that this policy has attracted criticism in some quarters as being either too narrowly focused on food production or as representing a contradiction in terms.
The Balancing Act of Producing More Food Sustainably

Sustainable Intensification in Agriculture: Premises and Policies tries to do two things: first to lay out the logic on which it rests (why is it needed?); and second, to highlight other social, environmental, economic and ethical concerns that SI needs to engage with if it is to contribute to delivering a sustainable and food-secure system.
Climate Blog

The Oxford Martin Programme on the Future of Food, working closely with the Food Climate Research Network and other research and policy organisations, has been involved in developing and discussing the issues surrounding Sustainable Intensification.
Oxford Martin Programme on the Future of Food

Sustainable Crop Production Intensification from the website of the Food and Agriculture Organization of The United Nations (FAO UN)
Sustainable Crop Production Intensification