设施和露天栽培下有机菜地土壤氮素矿化和硝化作用的比较研究

矿化作用和硝化作用是土壤氮素转化的主要途径,通过室内培养试验,对设施和露天栽培方式下有机菜地土壤氮素的矿化与硝化作用进行了比较研究。结果表明,除培养第1d外,设施有机菜地土壤氮素矿化量、矿化率在整个培养期间都显著高于露天有机菜地土壤;设施有机菜地土壤硝化量、硝化率在培养前两周内高于露天有机菜地土壤;设施有机菜地土壤矿化与硝化作用总体比露天有机菜地土壤强烈。矿化作用可能与全氮、C/N、微生物活性关系密切,而硝化作用强弱可能与微生物活性有关。无论施肥与否,设施有机菜地土壤N2O排放速率在培养期间总体高于露天有机菜地土壤,前者N2O累积排放量显著高于后者,这可能与土壤C/N有关。

生物炭对有机菜心产量、品质及水分利用的影响

为探究生物炭对提升有机菜地土壤保水能力与菜心水分利用的作用,基于田间小区定位试验,研究不施肥(CK)、单施有机肥(MC0,110 t/hm2)、有机肥+低量生物炭(MC1,110 t/hm2+8. 5 t/hm2)和有机肥+高量生物炭(MC2,110 t/hm2+17 t/hm2)对土壤水分动态以及有机栽培菜心产量、品质及水分利用效率的影响。结果表明,有机肥配施生物炭可显著提高有机菜地表层土壤(0～20 cm)含水率,增加0～70 cm土壤贮水量,与处理MC0相比,处理MC1和MC2全生育期平均含水率分别提高4. 7%和8. 6%(P <0. 05),0～70 cm土壤贮水量分别提高12. 3%与3. 4%。CK处理0～20 cm土层含水率变化幅度大(10. 5%～31. 2%),处理MC1变化幅度相对较小,为15. 4%～30. 4%。相比处理MC0、MC2和CK,处理MC1可显著促进菜心生长,增加产量,改善菜薹品质。菜心株高、叶片数和叶围面积均以处理MC1为最高,相比处理MC0,处理MC1生物量与产量分别提高36. 7%、59. 1%,而硝酸盐含量降低20. 0%～44. 3%。与MC2、MC0和CK相比,处理MC1周年耗水量分别降低3. 6%、6. 8%和13. 7%(P <0. 05),而产量水分利用效率分别提高49. 8%、75. 7%和2 264. 8%(P <0. 05),生物量水分利用效率分别提高45. 4%、46. 6%和720. 1%(P <0. 05)。处理MC2与MC0相比,菜心产量和水分利用效率虽明显增加,但均显著低于处理MC1。研究结果可以为西北旱区有机蔬菜合理制定培肥制度提供理论依据。

Impact of Organic Vegetable Production System in Kiambu and Kajiado Counties of Kenya

Though there are many documented reasons that make farmers to adopt organic farming system, economic benefits present a major motivation. The study was conducted to evaluate the impact of organic production system on profitability of smallholder vegetable production systems in the two counties so as to appraise its contribution to improvement of rural livelihoods. The study collected data on costs and returns for a sample of 208 smallholder vegetable farmers who were composed of 78 organic and 130 conventional farmers. Impact of organic production system was evaluated using propensity score matching technique. Organic vegetable production system was found to have a positive significant impact of increasing farm gross margin by US$0.58 representing 89.5% among smallholder producers in Kiambu and Kajiado Counties of Kenya. The study recommended promotion of organic production system as a tool that can be used to improve livelihoods especially in the rural areas.