Changing practices mean more producers now opt for whole-farm soil testing, resulting in detailed data for every paddock.
"I will then sit down with the farmer and go through the results, coming up with a tailored fertiliser plan for each paddock," she says.
"Some paddocks won't receive any fertiliser, others will be given a specific blend to rectify deficiencies."
Brenna grew up on a sheep and beef farm in Dannevirke and says she knew from a young age she wanted to work outdoors.
"I didn't want to be stuck in an office, but I wasn't entirely sure what is was I wanted to do."
Brenna was a boarder at Feilding High School and helped get the school's first TeenAg club off the ground in 2012.
She went on to study a Bachelor of Agricultural Science (Honours) at Lincoln University.
As Brenna neared the end of her studies, she applied for a place on Ravensdown's coveted development programme.
She was one of 12 graduates accepted in her intake.
The programme provided an invaluable training ground, and helped her see New Zealand.
"Trainees are in the development programme for a minimum of six months," says Brenna.
"We all start in Christchurch and then get seconded to different regions to fill in for agri managers who are on leave."
Last August she moved to Taranaki for a six-month posting, which she has just completed.
"I loved it there. Both the Ravensdown team and local farmers were so supportive and willing to teach me about the region's climate and soils," she said.
"For example, Taranaki soils are really deficient in potassium, but soils back home in Dannevirke are low in sulphur."
Being a member of NZ Young Farmers made the move easier.
"When I got to Taranaki I didn't really know a lot of people, so I joined Central Taranaki Young Farmers," she says.
"NZ Young Farmers is a great way to meet like minded people especially when you're new to an area.
"But it turns out I did know some people. I got to the first meeting and I ran into people I knew from university and through NZ Young Farmers, which was pretty cool," she said.
Brenna fully immersed herself in the region, even running Ravensdown modules at two qualifying events for the FMG Young Farmer of the Year.
She has some helpful advice for high school students considering a career in the primary industries.
"Know what university you want to attend and make sure you're taking the right subjects in Year 13. My other key tip is to apply for scholarships. There are loads available, especially for agriculture. Many close in August, so be prepared and get your application in early."
"Apply even if you don't fit the scholarship criteria because if you're the only applicant you could still be successful," she says.
One of the scholarships on offer is the PKW-Ravensdown Scholarship for whānau of Parininihi ki Waitotara shareholders.