Major factors influencing the selection, quantity, time and method of application of manures and fertilizers are:
Soil factors – They most important factors are, soil physical condition (texture), soil fertility and soil reaction.
• Poor physical condition of the soil leads to poor plant growth due to impeded drainage, restricted aeration and unfavourable soil temperature. In this condition nutrients will not be used efficiency.
• Optimum soil moisture regime is essential for efficient use of fertilizers by crops.
• The availability of nutrients is poor in coarse textured soil when compared to fine textured soils. The coarse textured soil needs more frequent application of fertilizers when compared to heavy textured soil.
• The higher the fertility of soil, the lower is the response to manures and fertilizers.
• When the organic matter of the soil is higher, the response to fertilizer by crops is more.
• Soil reaction is important for selection of right type of fertilizers Rock Phosphate is advantageous in acid soils.
• The response of crop to fertilizers varies with the nature of crop and variety of the crop.
• The fertilizer responsiveness of a plant depends on the cation exchange capacity (CEC) of the roots. The root CEC of dicotyledonous plants is much higher than that of monocotyledonous plants. Plants with higher CEC absorb more of divalent cations (Ca, Mg) whereas plants with low CEC absorb more of monovalent ions (K, Na).
• The ability of the crop to absorb nutrients from the soil depends upon the size of the root system (root length and spread) and characteristics like root surface and root hair density etc. Large ramifying root system absorbs more nutrients.
• The association of mycorrhizal fungi with the roots of plants grown under conditions of low soil fertility, increases the ability of plants to absorb nutrients such as P, K, Cu and Zn. Normally N, P and complete fertilizer application reduce the presence and activity of Mycorrhiza.
Agronomic factors – Fertilizer responsiveness of crops depends on timely sowing, proper spacing, proper dose, time and method of fertilizer application.
• Climatic factors – Under drought and excess moisture condition, foliar spray can be recommended. In high rainfall area, split application of fertilizers and application of slow release nitrogenous fertilizers are recommended.
• Yield goal – The economic yield or potential yield or targeted yield decides the quantity of manures and fertilizers application. For higher crop yield optimum or maximum amount of fertilizers are to be applied.
• Cost of fertilizers – Not only the cost of fertilizers and manures but also the cost of together produce decide the quantity of manures and fertilizer to be applied i.e., depend on the profit from the crop. It may be maximum profit or maximum rate of return per rupee invested.
• Availability of manures and fertilizers – Timely availability of manures and fertilizers, transport facility and labour for application decides the quantity. Now-a-days, manures are not available to the required level due to various reasons.
Slow release fertilizers – are developed to prevent the loss of nutrients by leaching and nitrification. It releases nutrients slowly and uniformly and increases the fertilizer use efficiency. Examples: Neem coated Urea, Sulphur coated Urea, Lac coated Urea, Tar coated Urea, N-Serve, Isobutylidine di Urea (IBDU), Thiourea etc.
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