What factor increases the amount of sunlight in a vineyard?

Latitude is the correct choice because it directly influences the amount of sunlight a vineyard receives. Areas closer to the equator typically experience more direct sunlight throughout the year compared to regions at higher latitudes, which can have longer periods of reduced sunlight due to the tilt of the Earth. Sunlight is crucial for photosynthesis, a process that affects grape development and ultimately the quality of the wine produced.

In contrast, wind direction can influence the microclimate of a vineyard but does not impact the overall sunlight directly. Soil composition plays a significant role in water drainage and nutrient availability but is unrelated to sunlight exposure. Humidity affects the moisture content in the air and can influence disease pressure and growth conditions, but it does not increase sunlight levels. Thus, latitude remains the key factor in determining sunlight exposure in a vineyard setting.