Soil and Nutrition Summary

Cotton has low tolerance to acidity, aluminum toxicity and low calcium content, and acidity alleviation is essential to achieve high crop yields. Liming will increase pH, neutralize exchangeable aluminum and increase base saturation. The crop will also benefit from increases in cation exchange capacity (CEC) and the availability of N, S, P, B and Mo. It promotes improvements on root growth, allowing better nutrient use efficiency. Liming should be performed at least two months prior to planting with subsequent incorporation by plowing and harrowing.

Fertilizer recommendations should replace nutrients removed by fiber and seed, in order to replace losses and avoid soil degradation. Crop rotation, nutrient recycling and conservation tillage are very desirable as these measures reduces soil erosion and nutrient losses and help to maintain and/or improve soil productivity.

In order to assess the nutrient requirements of the cotton crop, soil and leaf analysis are important tools and must be used.
All nutrients are important for efficient cotton production. Key nutrients that particular attention should be taken on Australia cotton soils are; nitrogen, phosphorus, potassium, sulphur and zinc.

Nitrogen supports plant growth which develops the plant structure and fruiting sites for bolls set. It is required throughout the whole growing season but the peak demand for nitrogen is during flowering, with 55% taken uptake during this period. Insufficient nitrogen availability will reduce production of leaves & stems, reducing potential fruiting sites which lowers boll numbers and reduces yield. Higher yielding crops are requiring greater flux of nitrogen per day as the growing period has not increased greatly but yields have increased. Peak nitrogen uptake is closer to 5 kg/ha/day in these crops, which is placing larger demands on the soils and the timing of nitrogen fertilizer applications.

Phosphorus plays an important role in the plant’s production of energy. A shortage of phosphorus will reduce a plant vigour, which restricts root and foliage growth, delaying and reducing production of fruiting sites and crop maturity. Under cool conditions, cotton responds to low rates of phosphorus applied with the seed. Crop removal applications of phosphorus should be well distributed in the hill or bed as cotton responds to good phosphorus nutrition, not bands of phosphorus fertilizer.

Potassium is integrally involved in metabolism and plant water relations, it is an enzymatic activator and is essential to photosynthesis, among other functions. Apart from its enzymatic functions, in cotton potassium plays a particularly important role in fiber development and a shortage will result in poorer fiber quality and lowered yields. K also reduces the incidence and severity of wilt diseases.

Zinc is very important for production of growth hormones, chloroplast development, protein synthesis and detoxification of oxygen radicals which are formed due to stress; extreme sun light, water stress. . Zinc availability throughout the growing season is very important as approximately 73% of total zinc uptake occurs during flowering.

Guidelines for nutrition management in cotton

-          Cotton has high requirement of N and K.

-          Phosphorus and zinc nutrition is important for early plant growth, both root and shoot.

-          Roots begin to decline after flowering as the cotton plant shifts its energy from root to boll development.

-          Foliar applied zinc can supply the large uptake of zinc during the flowering period.

-          As bolls begin to develop, they become much stronger carbohydrate sinks than roots and shoots. At this stage, root and shoot growth slow, and boll development dominates plant growth, and the widely established roots continue to supply large quantities of water and nutrients to the shoot.

-          During the boll enlargement and fiber elongation phase, the development of the fiber is very sensitive to adverse environmental conditions. Low water availability, extremes in temperature and nutrient deficiencies (especially potassium) can reduce the final fiber length.

-          Potassium nitrate as foliar application can avoid late season deficiency.

-          Always take into consideration local conditions and soil status when planning a crop nutrition program.