The researchers studied how adding water soluble phosphate to rock phosphate affects its availability to cabbage and rye plants. They used labeled phosphates in pot experiments to see how plants absorb phosphorus from the soil and rock phosphate. The results showed that the ratio of rock phosphate to soil phosphate absorbed by plants can vary, with a low ratio indicating less rock phosphate uptake compared to soil phosphate. This means that adding water soluble phosphate can influence how plants utilize rock phosphate for growth.