Timed release of phosphorus improves growth in tomatoes

Fertilisers are essential for sustaining crop yields, but their use must be carefully managed to ensure a timely delivery of nutrients that aligns with the plants’ needs. A recent study by Ngo and colleagues, published in AoB PLANTS, delves into this topic, focusing on tomatoes and their growth responses to different fertiliser applications. The researchers observed how tomatoes reacted to various rates of nitrogen and phosphorus – nutrients critical for plant health – from both organic and inorganic sources. Surprisingly, they found that blending these sources can lead to rapid and substantial growth in tomatoes while decreasing the need for additional nitrogen.

Ngo and colleagues uncovered intriguing interactions between phosphorus (P) and nitrogen (N) rates and their sources on the growth of tomato plants over time. Using high-tech shoot phenotyping techniques, they found that different forms of phosphorus – inorganic, organic, or a mix of the two – significantly influenced the amount of plant-available phosphorus in the soil.

Surprisingly, despite equal amounts of phosphorus being added to the soil, organic sources provided half as much plant-available phosphorus as the inorganic source. This gap can be explained by the fact that only about 37% of the total phosphorus in the organic matter is readily available for plant uptake. Consequently, this difference in initial phosphorus availability likely led to more pronounced discrepancies in shoot growth between plants that received different phosphorus sources. 

However, the plot thickens as we move through the growth timeline. Over time, the combined use of inorganic and organic sources resulted in similar, if not better, shoot growth than organic phosphorus alone. This is because inorganic sources provide a quick initial boost, while organic sources sustain phosphorus supply over time. The mixed approach can also reduce the carbon-to-phosphorus ratio in soil amendments, potentially boosting microbial activity and improving plant phosphorus uptake. This approach paves the way towards more sustainable fertiliser practices, minimising reliance on mined phosphorus resources while promoting the recycling of agricultural wastes.

Adding an extra layer of complexity, the team observed that nitrogen availability also plays a crucial role in determining shoot growth. While the inorganic phosphorus source fueled early shoot growth, maintaining this growth required higher nitrogen levels. The organic phosphorus source, which includes additional nitrogen, proved beneficial in this regard, enabling sustained plant growth. This might mean that organic sources, such as chicken litter, could offer indirect benefits by contributing to nitrogen nutrition, thus lessening the need for conventional nitrogen fertilisers.

Phosphorus is a problem. Using phosphorus fertilisers helps increase its concentration in the soil, thus boosting crop yield. However, over time, repeated applications can lead to a surplus of phosphorus, which can pollute water sources and negatively impact aquatic ecosystems and human health. Hence, there’s a need to balance maintaining crop yields and mitigating environmental impact.

Traditionally, inorganic phosphorus fertilisers derived from finite phosphate rock deposits have been used. But these are becoming increasingly expensive and less accessible. Conversely, organic materials like wheat straw and poultry manure, which are often by-products of crop and livestock production, contain a high concentration of nutrients, including phosphorus. There’s potential to utilise these organic materials to reduce reliance on inorganic phosphorus and repurpose waste.

These findings could have significant implications for sustainable agriculture. By understanding the effects of different nutrient sources on crop growth, we could potentially optimise farming practices to maximise yields while minimising environmental impacts.

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Ngo, H.T.T., Cavagnaro, T.R., Jewell, N., Brien, C.J., Berger, B. and Watts-Williams, S.J. (2023) “High-throughput shoot phenotyping reveals temporal growth responses to nitrogen and inorganic and organic phosphorus sources in tomato,” AoB PLANTS, 15(2), p. lad011. Available at: https://doi.org/10.1093/aobpla/plad011.