Effects of site and nitrogen management on growth and grain quality for malting of winter barley

Abstract

The project 'Interpretation of site/treatment effects on growth and N uptake of winter barley in relation to quality criteria, particularly %N in barley for malting' (0080/2/87) was funded by the Home-Grown Cereals Authority from 1988 to 1990. The programme of 17 experiments with two nitrogen treatments at six sites over three years was carried out by Rothamsted Experimental Station, Newcastle University, Queen's University Belfast, Nottingham University and ADAS Soil Science. Preliminary analysis and interpretation of the data on dry matter production and its partitioning, N uptake and its partitioning, phenological development, leaf area production and shoot production, were reported in Project Report No 48 . Further analysis of the database was funded by the HGCA in 1992 (0007/1/92) and output from this is presented and discussed in this report.

Partitioning of dry matter (DM) and nitrogen to the grain, i.e. DM harvest index and nitrogen harvest index, together with %N in the grain, were highly conserved characteristics of crops. Grain yield, total DM production and nitrogen offtake were very responsive to the availability of nitrogen and the effects of site and year. The contribution of stored carbohydrate reserves to grain yield was very variable from experiment to experiment and nitrogen had no clear influence on it. The contribution from nitrogen taken up before anthesis to the nitrogen content of the grain was much more consistent from experiment to experiment.

A database was constructed from the data collected on all characteristics at each centre. Verification of the data involved checking for outliers and examining residuals. The time series of data on dry weights were summarised using the Gompertz* function and the parameters from these functions used to calculate variates describing the patterns of growth. Variates describing the patterns of nitrogen uptake were derived using fitted dry weights and actual nitrogen concentrations. Site x Year matrices for the variates were analysed using ANOVA with corrected variance ratios and standard errors.

Fitting of the Gompertz function provided reliable and valuable summaries of the time series of total and ear dry weights. The agreement between the modelled and the observed data was substantial, giving confidence in the fitting procedures adopted. However, the fitted growth patterns did not correlate with either stages in crop development or calendar date.

*Gompertz Function: y = A + C-(-b(x-m)) function allows the Relative Growth Rate to decrease exponentially with time and with growth achieved.

Influence of Nitrogen, Site and Year on yield, carbohydrate production and partitioning and nitrogen uptake and partitioning

Economically important characteristics:

Grain yield
Grain yields varied in response to nitrogen and from site to site and year to year. Differences in ear numbers/m² accounted for variation in grain yield from year to year. The effect of nitrogen on grain yield was attributable to differences in both ear number/m2 and grain number per ear. Various combinations of the components contributed to differences in grain yield amongst the sites. Variation in total dry matter production rather than harvest index accounted for the effects of year and nitrogen on the components and grain yield. Harvest index as well as total dry matter production varied from site to site.

%N in the grain
Nitrogen concentration in the grain (%) varied between 1.17 and 1.88% in 32 of the 34 experimental treatments. The two remaining samples, which were from Sutton Bonington, had nitrogen concentrations of 2.18 and 2.54%. Although nitrogen harvest index was much lower, total N and grain N offtakes were markedly higher at Sutton Bonington than at the other sites resulting in these high %N's in the grain. Application of nitrogen resulted in increases in %N in the grain of up to 0.43% in most experiments, greater increases of 0.60- 0.77% being obtained at Sutton Bonington. Total N and grain N offtakes both increased in response to nitrogen application but nitrogen harvest index was lower in the fertilised than in the unfertilised crops.

Physiological characteristics:

Total dry weight
The beginning and end of the phase of rapid increase in total dry weight as derived from the fitted Gompertz functions was not consistent from experiment to experiment either in calendar date or in relation to development. Approximately 10-15% of the final dry weight was produced prior to the main phase of growth. By anthesis 60% of the final dry weight was present with the remaining 40% being produced during the grain filling period. Application of nitrogen usually increased the rate of growth. Growth rates in the fertilised crops were much less variable than in the unfertilised crops.

Ear dry weight
The large effect of nitrogen on ear dry weight varied to some extent from site to site in each year. The contribution of stored reserves to the increment in ear dry weight was very variable from crop to crop. In eight out of 13 experiments, utilisation of reserves was greater in the unfertilised than in the fertilised crops.

Total N content
Application of nitrogen had a significant effect on the total N content of the crop at harvest but the responses to nitrogen varied from site to site and from year to year. In the unfertilised crops 34-63% and in the fertilised crops 12-88% of the final total N content, was present at ZGS 30/31. The fertilised crops took up 6.3-9.3g/m2 and the unfertilised crops 0.3-3.5g/m2 nitrogen between the time when nitrogen was applied to the fertilised crops and anthesis. Two of the unfertilised crops and six of the fertilised crops lost 0.6-2.0g/m2 nitrogen between anthesis and harvest whilst the remaining crops, both fertilised and unfertilised, took up between 0.6 and 8.0g/m² nitrogen during grain filling.

Ear N content
Although application of nitrogen had variable effects on ear N contents at anthesis and harvest from experiment to experiment, the increment in ear N content and the contribution from pre-anthesis N uptake were markedly consistent in their response to nitrogen from site to site and year to year. Pre-anthesis uptake of nitrogen supplied 45% of the increment of 5.2g/m2 in ear N content during grain filling in the unfertilised crops. In the fertilised crops there was a much greater contribution, 80%, from pre-anthesis uptake to the increment of 8.5g/m2 in ear N content.

Shoot production and survival
In many crops most of the shoots were already present when nitrogen was applied. Maximum shoot number was not consistently reached at any particular growth stage. Final shoot number was very variable but the proportion of shoots surviving was reasonably constant from experiment to experiment. Both dry weight per shoot and N content per shoot were very variable from site to site and from year to year. Application of nitrogen had a variable effect on maximum shoot number but consistently increased survival by 15% so increasing final shoot number.

Mechanisms explaining carbohydrate production and partitioning

A number of approaches were used to describe and explain carbohydrate production and partitioning:

1. The components of yield provided a more detailed picture of the structure of the crop but are themselves net results of complex processes. The components confer a flexibility to cereal crops which allows them to respond continuously to and to exploit fully the variable weather conditions and supply of resources encountered in every cropping situation. Although the overall total dry matter production of the crop may be determined by the quantity of light intercepted, the crop's capacity to intercept all the available light over a long period of its life cycle and to utilise it depends on its ability to 'keep all its options open' until very late in the life cycle. In doing so it can avoid being severely limited by short term shortfalls and can capitalise on surpluses to produce what in effect is a relatively stable yield from situation to situation.

2. The rates and durations of production of dry weight as derived from the fitted growth functions were related to grain yield via a simple model and a preliminary analysis of the effects of limiting factors was conducted. Application of nitrogen increased the rate of growth, thereby increasing total dry matter production and as a consequence increasing yield. Site and Year had large effects on both the rate and duration of growth, and therefore, on total dry matter production. Harvest index varied from year to year and from site to site but was only minimally affected by nitrogen. Site and Year both had marked effects on grain yield.

3. The status of the crop at anthesis was considered as a pivotal point in growth and development, ear numbers and grain numbers having been finalised and crop capacity for photosynthesis and supply of stored reserves for remobilisation during grain filling having been established. The status of the crop at anthesis as shown by total dry weight, shoot number and dry weight per shoot, was not strongly associated with either the numbers of grain present at this stage, the grain productivity per shoot at harvest or the extent to which stored reserves contributed to grain yield. Stored reserves were utilised to a varying extent in grain growth, particularly when compared with the large and consistent effect of nitrogen on ear dry weight. It was not possible to determine if reserves were fully utilised in grain-filling, i.e. exhausted, or if some reserves were left unused because there was insufficient demand from the grains.

4. The relationship between total dry weight and nitrogen offtake was examined. Monteith's relationship between light interception and dry matter production was extended to include the influence of nitrogen on production of the light capturing capacity of the crop, i.e. its green area. Total dry weight was not strongly related to N offtake at any stage of growth although the nitrogen content of the unfertilised crops was more highly correlated with their dry matter production than was the nitrogen content in the fertilised crops. The unfertilised crops were also much more effective than the fertilised crops in utilising the nitrogen they took up to produce dry weight.

Mechanisms explaining nitrogen uptake and partitioning

Although apparent recovery of the applied nitrogen varied between 20 and 79% in those crops where it could be determined, uptake between the time when nitrogen was applied and anthesis was similar in all crops within each treatment. During grain filling the behaviour of the crops varied greatly, some losing nitrogen whilst others had uptakes of up to 8.0g/m2. However, the increments in ear N content and the amounts of nitrogen remobilised from pre- anthesis N uptake were similar in most crops within each nitrogen treatment.

Significant differences between the sites and variation from year to year in characteristics associated with grain yield and with nitrogen uptake of the crops only rarely led to high %N's in the grain. Consistent site differences in %N were not detected. The remarkably low sensitivity of %N in the grain to nitrogen availability to the crop is apparent from the small effect of the applied nitrogen on %N relative to its large influence on grain yield.

Implications for crop management

Prediction of %N in the grain at earlier stages in the life cycle was shown to be unlikely to be reliable using results from this programme. Although remobilisation of nitrogen taken up before anthesis was the major source of nitrogen for the grain, variation in uptake and other processes influencing losses of nitrogen from the crops during grain filling resulted in variation in grain N offtake and therefore, in %N in the grain. Crops maximise their production of dry matter using the nitrogen taken up, therefore, management for grain with low %N is consistent with management for optimum grain yields, i.e. maximum efficiency in utilisation of nitrogen.

Future work

. Further analysis of green area, nitrogen concentration and nitrogen:area ratio in this database.

. Further analysis of the relationships between dry matter production and meteorological variates in this database. Development of concepts and experimental techniques for understanding flexibility of cereal crops.

. Methods of definition of sites using weather and soil data and including an investigation of the implications of the scale of definition on modelling of crop behaviour.

. The nitrogen economy of crops during grain filling - an investigation of processes influencing uptake and loss of nitrogen by crops and internal factors governing the remobilisation of nitrogen to the grain.