Performance of three infiltration models under surge irrigation

Three models were developed to predict infiltration under a surge-flow irrigation regime. One model (2P) utilized the Kostiakov-Lewis infiltration equation. The other two models (2PF and 3P) utilized the modified Kostiakov-Lewis infiltration equation. All three models combined continuous-flow furrow irrigation volume-balance hydraulic models presented by Reddell and Latortue (1986, 1988) with a numerical variation of the Cycle Ratio-Time Model (CRTM) for surge irrigation presented by Blair and Smerdon (1987). The volume–balance component of the models estimated the soil's continuous-flow furrow irrigation infiltration function using first surge-cycle advance data. The numerical CRTM component used the estimated infiltration function in conjunction with the surge-flow irrigation infiltration opportunity-time to predict infiltration. An assessment of overall model accuracy was based upon an infiltrated volume root mean square error (RMSE) statistic. Overall, the 2PF model returned the lowest RMSE values and the 3P model was the next most accurate. The 2P model was the least accurate. While the 2PF model was the most accurate, this model has limited applicability since it requires inflow and outflow measurements throughout an irrigation event to evaluate the soil's basic infiltration constant. Despite its good overall performance, anomalous results from the 3P model suggest that further testing is needed. Although the 2P model was the least accurate of the three models evaluated here, and although it consistently underpredicted infiltration, it appears to be the most stable and effective of the three models evaluated. Received: 22 May 2000     

Incorporation of slow-release fertilisers into nursery media

Field application of fertilisers is frequently ineffective in supplying limiting nutrients during establishment of plantation trees in highly weathered soils in the humid tropics. An alternative strategy for more effective delivery of nutrients to establishing trees was investigated in a field experiment on Kolombangara in the Solomon Islands. Under routine operational nursery conditions, cuttings of Gmelina arborea and seeds of Acacia mangium were planted into a coir (composted coconut husks) potting medium to which a range of rates of slow-release fertilisers had been applied. The growth performance of this nursery stock was then measured during the first 14 months following planting in the field. Incorporation of slow release fertilisers into the nursery medium significantly improved the growth of both species in the field, with more than 100% increases in volume index associated with the highest rates of slow release fertiliser application. This strong nutrient response during tree establishment was in sharp contrast to the absence of any effect from much higher rates of surface applied fertilisers that had been observed in previous field experiments on this same soil type. The placement of the slow release fertilisers within the immediate proximity of roots of the establishing trees, and the subsequent effects of this in increasing their abilities to compete with regrowth vegetation for site nutrient resources probably accounted for the high effectiveness of this fertiliser strategy in enhancing tree growth.     

木麻黄根瘤中分离的三株弗兰克氏菌生长与培养方法的研究

比较了从不同来源的木麻黄根瘤中分离得到的三株弗兰克氏菌在两种浓度不同碳源培养基中的生长差异，结果表明：供试菌在以丙酮酸钠为唯一碳源时生长最好，其生长量为其它碳源的１．３－４７．７倍；最适合的碳源浓度为０．２３ｇＣ＼Ｌ。在三种不同的Ｆｒａｎｋｉａｘ菌地，通入无菌空气发酵培养培养能显著地提高弗兰克氏菌的生长量。同时还探讨了弗兰克氏菌的发酵条件。