What happens to phosphorus uptake in cool planting conditions?

When your spring or fall planting conditions are on the cool and wet side, you might need additional strategies to ensure young seedlings have access to sufficient phosphorus needed for growth. An early supply of phosphorus can have a long-lasting impact on crop yield potential.

Root growth critical

Plants need phosphorus very early, from the first stages of germination, for energy reactions, cell division, and growth. But phosphorus doesn’t move much in the soil, staying put mostly where it is placed during application. That makes root growth a critical step for young plants to be able to grow towards phosphorus in the soil. And any conditions that impact young crop root growth also impact the plant’s ability to access and use phosphorus.

Cold weather slows development

In the Midwest, where planting corn or winter wheat often occurs in cool and/or wet soil, young plants have slower root growth and may suffer from phosphorus deficiency at a critical time in the plant’s development. This can happen even if phosphorus levels in the soil are high enough (on paper) but not accessible by the young crop.

Starter fertilizers provide an effective option to deliver available phosphorus more directly to young seedlings until their root systems develop enough to move within the soil to find phosphorus. The practice involves a band application in or near the seed row at planting to place the fertilizer in a position where the crop can access it early in the season.

Jumpstart for cool soil conditions

Starter fertilizers are most beneficial when planting in cold, wet soil in early spring or late fall, regardless of the total fertility status of the soil. Cold and wet soil not only reduces root growth rate – and the ability of the plant to grow to reach phosphorus – but can also reduce the breakdown of nutrients into usable forms for the plant. Applying starter fertilizers is also important in reduced tillage crops where soil may be cooler because of the insulating factor of crop residue.

Young corn crops are the most responsive to starter fertilizer. Small grains respond positively to starter fertilizer applications especially in marginal fertility soils and for late fall planting. Giving young plants early season access to phosphorus in a starter fertilizer application places the fertilizers where the young roots will contact it soon after germination. As the root system grows and soil conditions warm up, the growing crop will then be able to grow and access the available phosphorus in the soil.

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