Effect of irrigation on tillering in wheat,triticale and barley in a water-limited environment

Summary The effect of irrigation on tillering and tiller mortality in varieties of wheat (Triticum aestivum and T. durum), triticale and barley was studied under field conditions. Low temperature in the early stages of growth promoted production of tillers whereas increase in temperature during extension growth phase increased tiller mortality. More than 1000 tillers m^–2 were produced with five irrigations but 40% or more died. With limited water availability tiller production was reduced but so was their mortality. Grain yield in wheat and triticale was positively correlated with productive tillers and negatively correlated with the maximum number of tillers produced in wheat and barley grown under limited irrigation conditions. Varieties with a capacity to produce fewer tillers were identified. Some of them proved more stable in yield. No correlation was found between tiller number and grain yield in the frequently irrigated treatment.     

A simulation of water allocation policies in times of water shortage

The use of a simulation package to study the consequences of various water allocation policies during time of water shortage is described. The study shows that simulation can be a valuable aid to irrigation scheme managers in their decision making.     

Alfalfa (Medicago sativa L.) water use efficiency as affected by harvest traffic and soil compaction in a sandy loam soil

Summary Traffic during alfalfa harvest operations can cause soil compaction and damage to newly growing stems. Root exploration for soil water and nutrients, forage growth dynamics, and final yield can all be affected. The objectives of this study were to determine the long-term effects of harvest traffic and soil compaction on water-use efficiency (WUE) of alfalfa grown in a Wasco sandy loam (coarse-loamy, mixed, nonacid, thermic Typic Torriorthents). Alfalfa was planted into tilled soil and managed with or without harvest traffic. Plants subjected to traffic during harvest had a significantly lower WUE two out of the three years studied compared to plants that were never subject to traffic. The second experiment examined whether planting alfalfa into compacted soil and managed with or without harvest traffic altered WUE. Soil compaction had no affect on alfalfa WUE. It was significantly lower when grown in compacted soil and subjected to harvest traffic. It is suggested that the decrease in WUE caused by harvest traffic may be explained by plants allocating carbohydrates to damaged shoots and crowns instead of to above ground forage production. The area of the field affected by harvest traffic, which damages newly growing stems, should be minimized to increase crop water use efficiency.     

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.     

Managing the water balance of The Fayoum Depression,Egypt

A study of the water balances of The Fayoum irrigated lands and Lake Qarun was made to investigate the management of the irrigation system and the efficiency of irrigation water use. The two water balances are strongly interrelated. The drainage flow to Lake Qarun and the water level of the Lake are in delicate balance. A rise in Lake level causes the inundation of adjacent land. Management of The Fayoum water balance assumes control over irrigation water flows, but this control has technical and organizational limitations. Also discussed is the influence of irrigation practices in The Fayoum on the water balance (e.g., the autumn flushing of fields and farmers' preference for not irrigating at night in winter). Notwithstanding a high overall efficiency, irrigation efficiency during the winter is low. The reasons for this are given, together with the constraints against improving system management. Improved uniformity of the division and application of irrigation water will enable a better technical control of flows and will result in better water management in The Fayoum. Abbreviations: FID — Fayoum Irrigation Department, 1 feddan (fe) — 0.4 ha, 1 mcm — 1 million cubic metres: an average annual flow of 3.17 m³/s gives 100 mcm, m³/fe.year — supplied volume (m³) per surface area (fe) per year: 1000 m³/fe.year equals 240 mm/year, MSL — Mean Sea Level     

Irrigation scheduling effects on yield and phosphorus uptake of cowpea

A line-source sprinkler irrigation system was used for irrigation-fertilizer cowpea (Vigna unguiculata [L.] Walp.) production studies. The relative merits and demerits of irrigating frequently but with smaller amounts of water than the design water application depth as compared to stage-of-growth and normal interval irrigation were investigated with five levels of fertilizer P, three water levels and five irrigation schedules.Dry matter production on the basis of forage produced was used as the yield indicator. The plants were harvested when the more advanced individuals reached the late boot stage immediately preceding the appearance of their inflorescences. P uptake was also measured.Statistical analyses of yield and P uptake gave a positive response of the crop to added fertilizer and irrigation water. Application of 70 kg/ha P₂O₅ produced the highest yields under all irrigation schedules. Irrigating too frequently was found to be detrimental; maximum yield under P fertilization was obtained with irrigations scheduled at half the design interval and with half the design irrigation depth. Uptake of P increased with yield.