When should a crop producer ensure seeds are in direct contact with fertilizer?

The practice of ensuring seed and fertilizer are in direct contact is particularly important when using low salt concentration fertilizers. Low salt concentration fertilizers are less likely to harm seed germination and root development. When fertilizers with higher salt content are placed in direct contact with seeds, they can create a detrimental saline environment that may hinder seed germination or even cause seed damage.

In contrast, using fertilizers with higher salt concentrations close to the seed can lead to osmotic stress, where the salt inhibits the seed’s ability to absorb water, leading to poor germination. Therefore, when working with low salt concentration fertilizers, placing them in direct contact with seeds can effectively provide nutrients while minimizing potential harm.

The other options highlight conditions or specific materials that may not inherently require or recommend direct contact of seeds with fertilizer. For example, very cold or very hot soil temperatures might impact seed germination, but they do not dictate the need for direct fertilizer contact in the way that the type of fertilizer does. Additionally, while urea is a nitrogen source, its direct contact with seeds typically requires caution regardless of the soil temperature, as high concentrations can be saltier.