Plant suitability is greatly affected by soil factors, including drainage, soil water holding capacity, pH, salinity, and alkalinity. Some species are particularly sensitive to standing water caused by poor drainage, and water holding capacity is determined by soil depth and texture and affects the need for irrigation. Acidity and alkalinity can be modified by soil amendments, but these may cause the crop to be unprofitable. Detailed soil data is available for the USA, but PRC soil maps are still at a low level of resolution.