Effects and interactions of phosphorus and sulphur on a mown white clover/ryegrass sward 3. Indices of nutrient adequacy

Abstract

Relationships were examined between relative yields of pasture with respect to phosphorus (P) and sulphur (S) applications, and clover herbage P and S concentrations and P/nitrogen (N) and S/N ratios in a P x S factorial fertiliser trial on a mown clover/ryegrass sward. The relationships between the yield of a treatment relative to the maximum yield obtainable with high rates of P alone (RY[P]) and both % P and P/N were affected by the application rate of S. S deficiency generally lowered the % P required for any given RY[P] but raised the P/N required. This latter effect was because S deficiency markedly lowered clover herbage N concentration. P deficiency had a similar but smaller effect on % S and S/N required for any RY [S]. S/N was much less sensitive to changes in clover S status than P/N was to changes in clover P status. This resulted from the strong stimulatory effect of S on clover % N. Relationships were also established between clover P and S adequacy indices and RY [PS] which is the herbage yield with P and S in physiological balance relative to the maximum yield with P and S in physiological balance. These relationships differed from those involving RY[P] and RY [S], requiring a higher value of the adequacy index for any specified RY. Nutrient concentrations (particularly of S and N) and ratios changed during a year, indicating that more than one sampling per year would be A96068 Received 16 September 1996; accepted 6 December 1996 necessary to determine whether the current fertiliser policy was succeeding in maintaining adequate and balanced nutrition throughout the year.

Pasture yield responses to sulphur fertilisers in relation to nutrient ratios in white clover

“…Clover S/N followed the same general trend over time for all treatments as clover S/P. Clover 100 S/ N ratios were lower than the optimum range of 4.8-5.0 (for 95%-98% RY) for adequate S nutrition (Sinclair et al 1997) for all treatments except the high residual S fertilisers, for most of the period over which they were measured ( Fig. 2B).…”

“…From recent research at an adjacent site, nutrient ratios in clover for balanced (e.g., S/P) and adequate (e.g., S/N) nutrition have been determined (Sinclair et al 1996a(Sinclair et al , 1996b(Sinclair et al , 1997. The use of different S fertilisers could result in different clover S/P and S/N ratios.…”

Sustainability of New Zealand high‐country pastures under contrasting development inputs. 1. Site, and shoot nutrients

“…They are also important in relation to litter decomposition and mineral cycling under different input managements. It has been suggested that shoot nutrient concentrations or ratios may be a better indicator of nutrient status than soil nutrient concentrations (Sinclair et al 1997). The approach of this study is that each species has a particular niche within the range of environmental and management conditions in the high country and that, accordingly, it may be necessary to define the shoot nutrient concentrations for a range of different species.…”

Relationship between P and N concentrations in timothy

“…Salette and Huché (1991) extended this approach to other nutrients such as P and K. Because of the similarities in the decrease in N and P concentrations with increasing shoot biomass, it was proposed to use the P:N ratio for diagnostic purposes (Salette and Huché 1991;Duru 1992;Duru and Ducrocq 1997). The use of P:N ratio to detect the nature of nutrient limitations was also proposed by Koerselman and Meuleman (1996) on natural ecosystems in the Netherlands and by Sinclair et al (1997) on cut white clover/ryegrass swards in New Zealand.…”