The effect of the administration of Solanum malacoxylon on the chick.

Replacement of the drinking water of chicks maintained on a normal mixed protein diet with an aqueous extract containing the equivalent of 5 g of the dried leaves of Solanum malacoxylon (DLSM) per 100 ml for one month produces a hypercalcaemia (23-49 per cent), hypomagnesamia (28-37 per cent), hypophosphataemia (26-34 per cent), hypouricaemia (29-34 per cent) and a decrease in plasma alkaline phosphatase activity (54-98 per cent). The ash content of the defatted, dried tibiae and the body weight of the DLSM treated chicks were also significantly lower (37-7 per cent and 17-79 per cent respectively) than the corresponding values for the untreated birds. The results obtained are similar to those reported for hypervitaminosis D3 in the chick.     

Ergovaline does not alter the severity of ryegrass staggers induced by lolitrem B

AIM: To investigate a possible interaction between lolitrem B and ergovaline by comparing the incidence and severity of ryegrass staggers in sheep grazing ryegrass (Lolium perenne) containing lolitrem B or ryegrass containing both lolitrem B and ergovaline.

METHODS: Ninety lambs, aged approximately 6 months, were grazed on plots of perennial ryegrass infected with either AR98 endophyte (containing lolitrem B), standard endophyte (containing lolitrem B and ergovaline) or no endophyte, for up to 42 days from 2 February 2010. Ten lambs were grazed on three replicate plots per cultivar. Herbage samples were collected for alkaloid analysis and lambs were scored for ryegrass staggers (scores from 0–5) weekly during the study. Any animal which was scored ≥4 was removed from the study.

RESULTS: Concentrations of lolitrem B did not differ between AR98 and standard endophyte-infected pastures during the study period (p=0.26), and ergovaline was present only in standard endophyte pastures. Ryegrass staggers was observed in sheep grazing both the AR98 and standard endophyte plots, with median scores increasing in the third week of the study. Prior to the end of the 42-day grazing period, 22 and 17 animals were removed from the standard endophyte and AR98 plots, respectively, because their staggers scores were ≥4. The cumulative probability of lambs having scores ≥4 did not differ between animals grazing the two pasture types (p=0.41).

CONCLUSIONS AND CLINICAL RELEVANCE: There was no evidence for ergovaline increasing the severity of ryegrass staggers induced by lolitrem B. In situations where the severity of ryegrass staggers appears to be greater than that predicted on the basis of concentrations of lolitrem B, the presence of other tremorgenic alkaloids should be investigated.     

The growth and nitrogen economy of rice under sprinkler and flood irrigation in South East Australia

Summary ¹⁵N balances were compared in rice (Oryza sativa L., cv. Calrose) grown under continuous flood (CF) or sprinkler irrigation. Two sprinkler treatments with irrigation frequencies of once (S1W) and thrice (S3W) per week were studied. Five atom %¹⁵N-labelled urea (60 kg N ha^–1) was applied to microplots either 36 or 84 days after emergence (DAE). An equivalent amount of unlabelled urea was applied at the other application time, so that each microplot received a total of 120 kg N ha^–1 in an equal split. There was no significant effect of irrigation treatment on recovery of urea N by straw. Straw recovery from urea applied 36 DAE was almost half that from an application 84 DAE, and time of urea application produced a similar effect on recovery in grain. Grain recovery in S1W was less than half that in CF and S3W for both application times. Total plant recovery of urea N applied 36 DAE was similar for all irrigation treatments (average 29%), but for urea applied 84 DAE total plant recovery in CF (67%) was significantly higher than in S1W (49%). Total N uptake in the plant tops was considerably lower in both the sprinkler-irrigated treatments when compared with CF, and this was mostly due to reduced soil N uptake in S3W (one-half) and S1W (one-third). The proportion of N derived from fertilizer in the plant tops increased from 40% in CF to 60% in S1W. Immobilization of applied N in the soil of the sprinkler-irrigated treatments was greater than in CF by factors of 1.5 (S3W) and 2 (S1W). Immobilization of urea N applied 36 DAE was almost 50% greater than immobilization of urea N applied 84 DAE. There was a trend for lower losses of fertilizer N with sprinkler irrigation (mean loss 18% of the applied N) compared with CF (27%). Within all irrigation treatments, the loss from urea applied 36 DAE was more than double the loss from urea applied 84 DAE. An additional study in CF compared the ¹⁵N balance for split application versus a single dose applied 36 DAE (before permanent flood). Split application resulted in significantly increased plant recovery of applied ¹⁵N, and this was largely associated with increased recovery in the grain. Slightly more fertilizer N was immobilized in the soil with a single application. The effect of application method on N loss was not significant.     

The growth and nitrogen economy of rice under sprinkler and flood irrigation in South East Australia

Summary Dry-seeded rice (Oryza sativa L., cv. Calrose) was subjected to 4 irrigation treatments — continuous flood (CF) and sprinkler irrigation at frequencies of one (S1 W), two (S2W) and three (S3W) applications per week — commencing 37 d after 50% emergence (DAE). The amount of water applied was calculated to replace water lost by pan evaporation. Urea (120 kg N ha^–1) was applied in a 1:1 split 36 and 84 DAE, and there were also unfertilized controls for each irrigation treatment. Amounts of nitrate (NO ₃ ^– ) in the soil were very low throughout the growing season in all treatments, despite regular periods of draining which lasted for up to 7 d in SlW. In all irrigation treatments, the majority of the fertilizer nitrogen (N) was located in the top 20 mm of soil. After each application of fertilizer, levels of mineral N in CF declined rapidly, while levels in S3W and S1W remained high for 1–2 weeks longer. The poor growth of sprinkler-irrigated rice was not due to lower amounts of mineral N in the soil. The greater persistence of fertilizer N in the sprinkler-irrigated treatments was probably due to reduced root activity near the soil surface because of frequent periods of soil drying in between irrigations. Net mineralization of soil N in the unfertilized sprinkler-irrigated treatments was reduced by about half compared with CF.On average, the quantity of water applied (1.2–1.4 × EP) to the sprinkler-irrigated treatments appeared to be sufficient to meet the evapotranspiration demands of the crop, except possibly around flowering time. However, the plants may have suffered from moisture stress in between irrigations. Soil matric potential data at 100 mm suggested little water stress in the sprinkler-irrigated treatments during the vegetative stage, consistent with the similar tiller and panicle densities in all irrigation treatments. However, the crop was stunted and yellow and leaf rolling was observed in the sprinkler-irrigated treatments during this period. Soil matric potential data at 100 mm indicated considerable water stress in S1W beyond the commencement of anthesis, and in S2W during grain filling, consistent with the reduced floret fertility and grain weight in those treatments.     

Performance of CERES-Rice and CERES-Wheat models in rice–wheat systems: A review

Rice–wheat (RW) systems are critical to food security and livelihoods of rural and urban poor in south Asia and China, and to regional economies in southeast Australia. The sustainability of RW systems in south Asia is, however, threatened by yield stagnation or decline, and declining partial factor productivity, soil organic C and water availability. Crop models potentially offer a means to readily explore management options to increase yield, and to determine trade-off between yield, resource-use efficiency and environmental outcomes. This paper reviews the performance of CERES-Rice and CERES-Wheat in Asia and Australia in relation to their potential application towards increasing resource use efficiency and yield of RW systems.

The performance of the models was evaluated using simulated and observed data on anthesis and maturity dates, in-season LAI and growth, final grain yield and its components, and soil water and N balances from published studies across Asia and Australia, and then by computing the statistical parameters for the major characters. Over the four data sets examined for anthesis and six for maturity dates, CERES-Rice predicted those dates fairly well (normalised RMSE = 4–5%; D-index = 0.94–0.95), but over the 11 sets for grain and 4 for biomass yield, the predictions were more variable (normalised RMSE = 23% for both; D-index 0.90 and 0.76, for grain and biomass, respectively). Model performance was poorer under conditions of low N, water deficit, and low temperatures during the reproductive stages. Over the three data sets examined, CERES-Wheat predicted the anthesis and maturity dates quite well (normalised RMSE = 4–5%; D-index = 0.94–0.99), and over eight sets for grain and two sets for biomass yield the model predicted them also reasonably well (RMSE = 13–16%; D-index = 0.86–0.97). Only one study evaluated the DSSAT RW sequence model with fairly satisfactory predictions of rice and wheat yields over 20 years with adequate N, but not the long-term change in soil organic C and N. Predictions of in-season LAI and crop growth, and soil and water processes were quite limited to investigate the robustness of model processes.

Application of models to evaluate options to increase water and N use efficiency requires the ability to perform well at the margin where deficit stress begins. While both models generally perform satisfactorily under water and N non-limiting conditions, the little evidence available suggests that they do not perform well under resource-limiting situations. We recommend that the models’ key processes under the water and N limiting conditions be further evaluated urgently. The DSSAT sequence model also needs to be further evaluated against observations for a range of locations and management using data from long-term experiments in RW systems.     

Community water management to intensify agricultural productivity in the polders of the coastal zone of Bangladesh

Paddy and Water Environment - Most of the lands of the southern coastal zone of Bangladesh are protected from tidal flooding and storm surges by embankments constructed during the 1960s and 1970s,...