To improve the water and pesticide holding properties of soil, one should:

Increasing the organic matter content in soil significantly improves its water and pesticide holding properties. Organic matter, such as decomposed plant material and animal residues, enhances soil structure, leading to better aggregation and porosity. This allows the soil to retain more moisture, which is crucial for plant health and overall soil fertility.

Furthermore, organic matter acts as a sponge, capable of holding onto water and nutrients, making them more available to plants. It also influences the soil's ability to bind and retain pesticides, which can lead to more effective pest control while minimizing runoff and environmental impact.

In contrast, decreasing organic matter would lead to poorer soil structure and reduced capacity for water and chemical retention, while increasing chemicals or reducing soil moisture is unlikely to directly enhance the soil's natural ability to hold water and pesticides effectively.