Crop nutrition

Getting your crop nutrition spot on is essential for maximising cotton yield. Too little nutrition will reduce your crop's yield potential, while too much fertiliser can impact your profitability through increased costs, contamination of groundwater, excessive vegetative growth in the crop, and related insect, disease and harvest problems. Increased cropping intensity can also result in the progressive depletion of soil nutrients - requiring more fertiliser to replace lost nutrition. 

So careful monitoring and management of nutrient levels is important to ensure yield potential is reached, without inefficient fertiliser application. Without regular monitoring, nutrition deficiencies may not be identified until symptoms appear - which may be too late! At that point, a reduction in yield is likely, despite remedial fertiliser applications.

So, it's important to get your crop nutrition right.

Key nutrients:

The key fertilisers used in cotton production are nitrogen (N), phosphorous (P), and potassium (K). Deficiencies are rare in other essential nutrients such as copper, boron, calcium, magnesium, sulphur, manganese, iron, zinc, cobalt and molybdenum.

Nitrogen (N):

Nitrogen (N) application is the most significant fertiliser input cost for Australian cotton growers. Nitrogenous fertiliser use has increased to the point where significantly more is being applied to commercial crops than industry best practice recommends and is required in most circumstances.

Nitrogen fertiliser use efficiency (NFUE): NFUE can be calculated as lint yield (kg/ha) divided by the total amount of fertiliser N applied. Long term measurement and monitoring strategies are required to distinguish between seasonally unavoidable low NFUE and low NFUE related to broader production system problems that can be addressed. Four broad factors influence nitrogen use efficiency:  soil type, irrigation practices, weather conditions and N application management. Poor NFUE from both pre and in-crop N application results from mechanisms such as volatilisation, denitrification and leaching, or temporary unavailability due to soil processes such as immobilisation. Optimal management of weeds, disease, sowing date, rate and variety will increase NFUE. 

Phosphorus (P):

Phosphorus (P) is highly immobile. Despite a high P content, many soils have low P availability, particularly under alkaline conditions. Phosphorus deficiency causes reduced seedling vigour, poor plant establishment and root development, delayed fruiting and maturity.  

Potassium (K):

Adequate potassium levels may improve yield and fibre quality, and reduce the incidence and severity of plant diseases. K deficiency symptoms vary depending on the growth stage of the crop. Premature senescence is a potassium related disorder that can occur regardless of the supply of potassium from the soil.  It is caused by the interaction of high boll loads and stresses such as water logging, cool, cloudy weather or subsoil constraints such as compaction, which restricts the plant's capacity to take up sufficient K at peak demand.

• Plan: Conduct soil sampling to determine physical and chemical soil properties. Calculate crop nutritional requirements related to expected yield, cropping history, cropping system nutrient losses, and soil conditions. Develop a long term crop nutrition plan to optimise nutrient use efficiency.
• Monitor: Regularly monitor crop nutrient status and conduct tissue analysis through leaf and petiole testing to assess deficiencies. During the growing season monitor plants and adjust crop nutrient programs for a targeted yield.  
• Manage: Implement a fertiliser plan and crop nutrition program before deficiencies in soil nutrients limit crop production.   

For more best practice information on crop nutrition, visit the myBMP Soil Health module.