An improved way to determine nitrogen fertiliser requirements of sugarcane crops to meet global environmental challenges

Abstract

Nitrogen (N) fertiliser management is increasingly important in sugarcane production as imperatives to reduce environmental impacts of N escalate. In this paper we report testing of a new concept for N management in sugarcane, the N Replacement system. This system relies on soil N cycling to 'buffer' differences in crop N needs and N fertiliser supply to individual crops, and aligns N applications with actual cane production over the longer-term rather than potential production. In 11 experiments, conducted in a wide range of environments over two to five crops, cane and sugar yields in the N Replacement treatment were similar to those achieved with the farmers' conventional N management, with a trend over successive crops for yields to increase relative to conventional management. At sites where experiments ran for at least 4 years, this trend resulted in cumulative sugar yields being higher in the N Replacement treatment. Average N applications were 35% lower in the N Replacement treatment, and N lost to the environment was estimated to be ∼50% lower. Soil N 'buffering' was adequate to maintain sufficient N supply to crops even when yields were up to 30% greater than expected. Thus, it is not necessary to align fertiliser applications to potential sugarcane yields, which are rarely achieved in practice. Our results show that the ecologically-based N Replacement system has promise to deliver superior environmental outcomes without significantly reducing production of sugarcane, and potentially other semi-perennial crops, in the tropics and subtropics. Further evaluation of the system will be beneficial, and there is scope for determining more sitespecific values of parameters in the system. However, care must be taken to evaluate the system over sufficient time frames (e.g. >2 crops) so that productivity improvement trends in the N Replacement system can be expressed.

Contribution of nitrogen from sugarcane harvest residues and urea for crop nutrition

“…However, at the same time this source showed the highest amount of uncountable N in the agro-ecosystem (37 %), hereafter named as N in other compartments -NOC. The NOC comprised N-NO 3 -losses by leaching below 0.60 m in soil profile, N-NH 3 volatilization from the soil or by plant canopy and by N-N 2 O denitrification Thorburn et al, 2011). Basanta et al (2003) evaluated the recovery of N-fertilizer by sugarcane in Brazil during three crops and found that 29 % remained in the soil, 42 % was used by plant and 29 % was lost as NOC, a result very similar to ours.…”

“…The crop residues incorporated into the soil during sugarcane pre planting operation were low effective to supply N for sugarcane nutrition (Table 2), but may have an important role for sustainability in tropical agro-ecosystems due to its contribution in supplying organic C, N and other nutrients for the soil organic matter in long-term (Thorburn et al, 2011). Indeed, the fate of above and below ground residues from last crop after 5 years (2005 to 2009) was in the soil (45 % and 59 % of total N present in the above and below ground of sugarcane residues, respectively), highlighting the importance of these materials in providing N to the soil (Figure 4).…”

“…Although these results may indicate that treatments with N fertilizer application was worse than without N, the whole balance revealed that N-fertilizer enhanced the availability of N from green harvest residues likely due to the reduction of the C:N ratio and higher intensity SOM degradation (Fortes et al, 2012;Vitti et al, 2010), added to the increase of crop performance and N uptake (Franco et al, 2008;Franco et al, 2010) and to the decrease in NOC ( Figure 5). Therefore, N fertilizer minimized losses in soil-plant system, stressing the importance of considering the interactions of N sources to manage long-term sugarcane fertilization programs (Thorburn et al, 2011). However, Khan et al (2007) stated that excessive N fertilization (> 200 kg ha -1 year -1 ) could lead to decreases in soil organic C stocks in the long-term due to higher degradation rates of crop residues.…”

“…Concluding, despite N fertilization being highly correlated to crop production it can also damage the environment, particularly under intense rainfall conditions Thus the maintenance of plant residues is essential for adequate crop nutrition while mitigating nutrient, soil and water losses (Liu et al, 2010;Thorburn et al, 2011). …”

Stalk and sucrose yield in response to nitrogen fertilization of sugarcane under reduced tillage

“…Therefore, N fertilization management is a challenge beyond the replacement of crop requirements and must take into account the agronomic and environmental impacts of mineral fertilizers and crop residues on the agroecosystems, as well as in C, N, and other nutrient balances in soil-plant-atmosphere (Dourado Neto et al, 2010;Fortes et al, 2011;Thorburn et al, 2011).…”