12.3.1 PAR and yield

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Crop yield commonly depends on the total amount of PAR intercepted, particularly when crop growth is not limited by other factors such as nutrient or water deficiency or temperature extremes. One example highlighting the importance of strong solar radiation for crop yield comes from a comparison of rice crops in Australia with those grown in tropical areas.

Rice in Australia is grown almost exclusively in southern New South Wales during dry summer months (November–March). Crops are fully irrigated and well fertilised and yield around 9t ha–1. This high yield is associated with high incident solar energy (commonly 10–15MJ m–2 d–1 PAR) during a long growing season. In tropical Asian countries rice is commonly grown under cloudy conditions during the wet season (June–November). Yield is lower (4–5t ha–1) even with high nutrient inputs, due to a shorter growing season and lower solar energy (often around 8–10MJ m–2 d–1 PAR). Experiments using shade cloths have also shown that rice growth and yield, in common with many other agricultural crops, are both reduced by decreased solar radiation (Sections 6.2, 6.4). Adverse effects of decreased solar radiation are most severe during grain filling.

 

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