Q1: Biuret formation in urea is kept at minimum (< 1 %), because it is

ANS:B - toxic and harmful to some crops.

Biuret, a compound formed by the condensation of two urea molecules, can be toxic and harmful to some crops when present in high concentrations. Here's how biuret can adversely affect plants:

1. Phytotoxicity: Biuret can act as a phytotoxic compound, meaning it has toxic effects on plant tissues. When plants are exposed to high levels of biuret, especially through fertilizer applications, it can lead to symptoms of phytotoxicity such as leaf burn, leaf yellowing, necrosis (tissue death), stunted growth, and reduced crop yields. These effects can vary depending on the sensitivity of the plant species and the concentration of biuret in the soil or applied fertilizer.
2. Nitrogen Toxicity: Biuret contains nitrogen, and when it accumulates in plant tissues, it can contribute to nitrogen toxicity. Excessive nitrogen levels can disrupt normal plant metabolic processes, such as protein synthesis and nutrient uptake, leading to physiological disorders and reduced plant health. Nitrogen toxicity symptoms may include leaf chlorosis (yellowing), leaf curling, root damage, and overall plant stress.
3. Reduced Nutrient Uptake: High concentrations of biuret in the soil or applied fertilizer can interfere with the uptake and utilization of essential nutrients by plants. Biuret can compete with plant roots for nutrient absorption sites and may inhibit the uptake of important nutrients such as nitrogen, phosphorus, potassium, and micronutrients. This can result in nutrient deficiencies, imbalances, and impaired plant growth and development.
4. Crop Sensitivity: Not all plant species have the same tolerance to biuret. Some crops are more sensitive to biuret toxicity than others. For example, certain grasses, legumes, and fruiting crops may be particularly susceptible to biuret damage, while other crops such as cereals or root vegetables may be less affected. Therefore, it's important to consider the sensitivity of specific crops when managing biuret levels in fertilizers applied to agricultural soils.

Overall, minimizing biuret formation in urea-based fertilizers helps to prevent phytotoxicity, nitrogen toxicity, and nutrient uptake issues in crops, thereby promoting healthier plant growth and maximizing crop yields. This underscores the importance of quality control measures in fertilizer production to ensure that urea products meet the necessary standards for agricultural use.