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Nutrient use-efficiency in current and redundant cotton cultivars

Ian Rochester and Greg Constable

CSIRO Plant Industry, LB 59 Narrabri NSW 2390 ian.rochester@csiro.au greg.constable@csiro.au
Cotton Catchment Communities Cooperative Research Centre

Abstract

We examined twelve cotton cultivars released between 1973 and 2006 in two field experiments at different sites in 2009 and 2010. Crop DM and nutrient uptake were measured at mid boll-fill and lint yield at crop maturity. Internal crop nutrient use-efficiency was determined by dividing lint yield by nutrient uptake. Results were consistent over the two years. Releases of improved cultivars increased lint yield by 1.5% per year. In concert with this, crop DM, N, P, K and S uptake increased by 0.9, 0.7, 0.5, 0.6, and 1.0% per year, respectively. The use-efficiency of P and K increased (P<0.05) with the release of improved cultivars while N and S tended to increase, but more slowly. We conclude that while lint yield has increased rapidly, crop nutrient uptake has increased less quickly, and crop nutrient use-efficiency has increased even more slowly.

Key Words

nitrogen, phosphorus, potassium, nutrition

Introduction

Nutrient uptake in cotton has increased with cultivar improvement. Crop biomass has increased substantially with newer cultivars, while the concentrations of only P and K have increased within the plant. One indirect selection occurring in breeding has been adaptation to sodic soil conditions in Australia which may allow greater P and K uptake (Rochester and Constable 2003).

Lint yield has increased due to selecting more productive genotypes. This can be attributed to several factors including more bolls on each plant (Kilby et al. 2012) and more lint on each seed. Disease resistance has also been improved in modern cotton cultivars that enable them to be more productive where disease pressure is high (Constable et al. 2001).

The effort in breeding more productive cotton cultivars has been directed more towards yield, fibre quality and disease resistance. No substantive effort has been directed towards breeding cultivars that use the nutrients they accumulate to produce lint more efficiently.

Methods

Two experiments were conducted in the 2008/9 and 2009/10 cotton seasons at Narrabri NSW Australia (150oE, 30oS). The soils at these sites were self-mulching medium grey clays overlying brown clay and classified as a fine, thermic, montmorillonitic Typic Haplusterts (Soil Survey Staff, 1996). The two sites chosen varied slightly in soil properties, cropping history and crop management. Both experiments were randomised complete block designs with 12 cultivars replicated four times: individual plots were 4 rows wide x 16 m long. Only N fertiliser was required and was applied prior to sowing cotton. The crops were grown on 1 m spaced ridges and flood irrigated according to commercial practice and insects were controlled when they exceeded commercial thresholds. Weeds were controlled with pre-emergent herbicides and mechanical cultivation.

The cotton cultivars were selected on the basis of them being an important commercially-grown cultivar. Some cultivars were grown for longer periods than others (Fig. 1). The cultivars contained no transgenic traits.

Figure 1. Commercial release date and period of availability of twelve cotton cultivars used in this experiment.

Above-ground biomass of cotton crops was measured 3 weeks before chemical defoliation when at least 25% of bolls were open; 1 m2 of crop which was cut, dried, weighed, milled and analysed for N concentration (using Kjeldahl digestion) to determine crop N uptake. Other nutrient concentrations were determined by ICP-AES after acid digestion. The crop was chemically defoliated when at least 60% of bolls were open. One central row of each plot was mechanically picked and weighed, and sub-sampled to determine lint percentage and lint yield.

Genstat 13 (Lawes Agricultural Trust, IACR, Rothamsted, UK, 2011) was used to test for differences using ANOVA. Linear regression analyses were performed using the SigmaPlot V11.0 program (Systat Software Inc., 2004).

Results

Crop nutrient uptake

Crop biomass assessed at mid boll-fill and quantities of N, P, K and S taken up by cotton were higher in the more recently released cultivars (Fig. 2). There were differences between the two sites for N and K uptake and biomass production. Averaged across sites, crop N uptake increased by 0.7 %/yr, P uptake by 0.5%/yr, K by 0.6 %/yr, S by 1.0 %/yr (**) and biomass by 0.9 %/yr (**). The concentrations of P and K (but not N or S) in the biomass significantly increased with date of cultivar release.

Figure 2. Nutrient uptake and crop DM produced by twelve cotton cultivars that were released over a 33 year period when grown in two irrigated fields (L1 and A3) near Narrabri NSW.

Lint yield

Lint yield increased at a rate of 31 kg lint/ha/yr (P<0.001); there were differences between the two sites. Similarly, lint percentage consistently increased by 0.13 %/year (P<0.001) (Fig. 3).

Figure 3. Lint yield and lint percentage of harvested seed cotton in twelve cotton cultivars that were released over a 33 year period when grown in two irrigated fields near Narrabri NSW.

Internal crop nutrient use-efficiency

Internal crop nutrient use-efficiency was defined as the lint yield divided by crop nutrient uptake. While there were differences between sites, crop P and K use-efficiency increased (P<0.05) with later released cultivars, but not N or S use-efficiency, although the trends were increasing (Fig. 4).

Figure 4. N, P, K and S use-efficiency in twelve cotton cultivars that were released over a 33 year period when grown in two irrigated fields near Narrabri NSW.

Conclusion

Improved nutrient use-efficiency has been achieved indirectly and as a consequence of selecting for yield.

Cotton yields have not plateaued, so nutrient uptake should continue to increase as we have shown for cultivars released over the past 33 years. Possibly, greater increases in nutrient use-efficiency could be achieved if the breeding effort was to be more specifically directed toward this objective (Baligar et al. 2001).

With continued cropping, soil fertility may decline if nutrients removed at harvest are not replaced. It is therefore important to improve the efficiency of nutrient use. As fertiliser costs increase, nutrient use-efficiency gains will be needed to maintain the productivity of cotton crops and the economic viability of cotton production.

While lint yield has increased rapidly, crop nutrient uptake has increased less quickly, and crop nutrient use-efficiency has increased even more slowly

References

Baligar, VC, Fageria, NK, and He, ZL (2001). Nutrient use efficiency in plants. Comm. in Soil Plant Analysis 32, 921-950.

Constable, G.A., Thomson, N.J. and Reid, P.E. (2001). Approaches utilized in breeding and development of cotton cultivars in Australia. In: Genetic Improvement of Cotton: Emerging Technologies. JN Jenkins and S Saha (Eds). Science Publishers, Enfield. pp 1-15.

Kilby, CR, Tan, DKY, Duggan, BL and Constable, GA (2012). Yield components of high-yielding Australian cotton cultivars. 16th Australian Agronomy Conference 2012. Capturing Opportunities and Overcoming Obstacles in Australian Agronomy. October 2012. University of New England.

Rochester IJ (2011). Assessing internal crop nitrogen use efficiency in high-yielding irrigated cotton. Nutrient Cycling Agroecosyst. 90, 147-156. DOI 10.1007/s10705-010-9418-9.

Rochester, IJ and Constable, GA (2003). Leaf nutrient concentrations in cotton cultivars grown in slightly sodic soils. Proceedings of the World Cotton Research Conference-3, Cape Town South Africa, Mar 9-13, 2003. A Swanepoel (Ed), Pretoria, South Africa, pp 681-5.

Soil Survey Staff (1996). Keys to Soil taxonomy, 7th edition. Natural Resources Conservation Service of USDA: Washington DC, 644 pp Systat Software Systems (2004). SigmaPlot for Windows. Version 11. Zhang Y, Hu W, Gao Y, Yao Y, Tang M, Hu G (2008). Fertilising irrigated cotton for high yield and high nitrogen use efficiency. Better Crops with Plant Food 92:6-7.

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