Field Crops

Sulfur (S) fertilization has increasingly become an important issue in crop management. In Argentina S deficiencies have been reported, but there has been no success in finding soil tests for predicting soybean response to S fertilization. The objectives of this study were to: (i) evaluate seed S and N:S ratio as a tool for identifying S deficient soybean crops in field conditions and (ii) determine shifts in stoichiometric relationships among nitrogen (N), phosphorus (P) and S in soybean seeds which can be used for identifying S responsive sites under field conditions. Seed samples from 20 field experiments designed to explore response to S fertilization in soybean were collected in a large area in the Argentinean Pampas region. Seed yield (SY) and P (%P), S (%S) and N (%N) concentration in seeds were determined. Different data analyses were tested in order to find an S deficiency index. Moderate SY responses to S fertilization were observed in the present study (i.e. relative SY was never below 75%). seed S concentration increased in response to S fertilization in most responsive sites, and N:S ratio was governed by variations in seed S concentration. Stoichiometric relationships were more accurate for identifying S responsive sites than using single variables (e.g. seed S concentration or N:S). The isometric variations among N, P and S suggest that the accumulation of these nutrients is proportional in seed tissue. A significant increase in the intercept of the stoichiometric relationship between N and S in S deficient crops was observed. An S deficient index (SDI) was calculated based on this difference that can be used as a diagnostic tool for identifying S responsive sites in soybean. The present study shows a novel approach for using stoichiometric concepts in fertilizer management in soybean.

The potential fl)r extending the production of winter oilseed crops into the drier region of the cereal belt of eastern Australia was examined by comparing canola, Indian mustard and Linola in field experiments in the contrasting environments of Junee and Condobolin, NSW. Junee is in the region where canola production is concentrated, and Condodolin is in the drier part of the cereal belt currently considered marginal for canola. Different rates of nitrogen (N) fertilizer were applied in all experiments, and there were two times of sowing at Condobolin. Wheat was grown for comparison in all experiments. Crop performance was evaluated over two seasons by measuring dry-matter production, grain yield, water-use efficiency, and seed oil and protein contents. Maximum grain yields of all crops at Junee were higher than at Condobolin, and yield responses to N fertilizer in both environments were greater in the wetter 1992 season than in the drier 1991 season. Canola and wheat showed the largest yield responses to N fertilizer, but Linola generally had the lowest yield responses because of poor seedling emergence at high N rates, intolerance of drought during grain filling (1991) and lodging (1992). Based on the overall growth and grain yield responses to N fertilizer, and on N (protein) removal in grain, it is suggested that about 25% more N be applied to canola than to wheat, that Indian mustard receive about the same N fertilizer rate as wheat, and that Linola requires about 20% less N than wheat. Sowing late at Condobolin, when there was below-average rainfall during grain filling (1991) reduced the yield of canola and Linola, but not Indian mustard. There was no yield penalty for sowing the crops late in 1992 when conditions were favourable during grain filling. Grain harvest indices based either on dry matter or the biosynthetic cost of seed production were higher tk)r wheat and canola than for Indian mustard and Linola, and were largely unaffected by the N treatments. A potential transpiration efficiency value of 12.5 kg seed ha i mm ~ was derived for the oilseeds based on the biosynthetic costs of seed production. Oil concentrations were reduced by dry conditions during seed filling, by late sowing and by N fertilizer. Oil concentrations were higher at Junee than Condobolin, due mainly to differences in ambient temperature as there was a 2.7% decrease in oil concentration tor each I°C rise in mean temperature during seed filling. Oilseed meal and wheal grain protein levels were more responsive to N fertilizer when conditions were dry during grain filling. Protein levels in oilseed meals were higher but wheat grain protein was lower when conditions were favourable during grain filling. The study indicated that there arc prospects for extending the production of canola and Indian mustard into drier regions of the cereal belt because, when sown early, they • Corresponding author. have similar water-use efficiencies to wheat based on the biosynthetic costs of grain production. While the yield of Indian mustard is limited by a low harvest index, its yield stability under dry post-anthesis conditions indicates greater potential than current canola cultivars for more marginal areas. Linola showed the least potential as an oilseed for the drier parts of the cereal belt because of shallow rooting and susceptibility to drought.

In eastern Washington, spring wheat cultivars that germinate and grow fast at low temperatures will provide the crop with a competitive advantage over spring emerging weeds in commercial production ®elds compared to cultivars that germinate and grow more slowly. The objective of this research was to develop a protocol to identify spring wheat cultivars that would germinate and grow more quickly at low temperatures. A novel data analysis method was used to separate the germination process into three components: (1) base temperature, (2) time to initiation of germination, and (3) germination rate. Spring wheat cultivars Edwall, Vanna, Wawawai, Wampum, Express, and Spillman were assessed through a series of controlled temperature gradient plate experiments. Base temperatures were not different P 0:1 across cultivars, and once germination was initiated, germination rates among varieties were uniform P 0:5. However, signi®cant P < 0:001 differences were detected among varieties for time to germination. A subsequent growth chamber experiment con®rmed differences in emergence and growth rate among spring wheat cultivars. Published by Elsevier Science B.V.

In maize, the effects of nitrogen (N) deficiencies on the determination of kernel number per plant (KNP) have been described only by changes in plant growth rate during the critical period for kernel set (PGRcp). We hypothesize that N availability affects KNP also through variations in biomass allocation to the ear, which determines a stable N concentration in this organ. Six maize hybrids of different breeding origin were evaluated in field experiments at two N levels (0 and 400 kg N ha À1 applied). Traits included were KNP and per apical ear (KN E1 ), and the allometric estimation of PGRcp, ear growth rate during the critical period (EGRcp), and N content and N concentration in different plant organs. We demonstrated that (i) N availability promoted differences among genotypes (G) in the response of EGRcp and KNP to PGRcp, (ii) variations in KN E1 were explained by EGRcp (r 2 = 0.64) and by ear N content at silking + 12 d (r 2 = 0.64), and (iii) ear N concentration was a highly conservative trait (range between 10.47 and 15.98 mg N g biomass À1 ) as compared to N concentration in vegetative tissues (range between 4.94 and 18.04 mg N g biomass À1 ). Three response patterns were detected among hybrids, one for which the relationship between EGRcp and PGRcp did not vary between N levels and experiments, a second one for which N availability affected this relationship, and a third one for which the response was affected by the year (Y) effect. These results, together with the high correlation between EGRcp and ear N content (r 2 = 0.88), evidenced the importance of both photo-assimilate and N availability on EGRcp and KNP determination. Values of 1.5-2.3 g ear À1 d À1 during the critical period and 0.49-0.70 g of N ear À1 at silking + 12 d were determined as thresholds for maximizing KN E1 , and both could be easily estimated by means of allometric models. # Abbreviations: EGRcp, ear growth rate during the critical period; Exp. n, experiment n; G, genotype; N, nitrogen; N n , N level; KN E1 , kernel number per apical ear; KNP, kernel number per plant; PGRcp, plant growth rate during the critical period; R 2 , onset of active grain filling; V n , leaf stage n; RKN E1 , relative KN E1 ; Y; year.