Purpose

Life cycle assessment studies on smallholder farms in tropical regions generally use data that is collected at one moment in time, which could hamper assessment of the exact situation. We assessed seasonal differences in greenhouse gas emissions (GHGEs) from Indonesian dairy farms by means of longitudinal observations and evaluated the implications of number of farm visits on the variance of the estimated GHGE per kg milk (GHGEI) for a single farm, and the population mean.

Methods

An LCA study was done on 32 smallholder dairy farms in the Lembang district area, West Java, Indonesia. Farm visits (FVs) were performed every 2 months throughout 1 year: FV1–FV3 (rainy season) and FV4–FV6 (dry season). GHGEs were assessed for all processes up to the farm-gate, including upstream processes (production and transportation of feed, fertiliser, fuel and electricity) and on-farm processes (keeping animals, manure management and forage cultivation). We compared means of GHGE per unit of fat-and-protein-corrected milk (FPCM) produced in the rainy and the dry season. We evaluated the implication of number of farm visits on the variance of the estimated GHGEI, and on the variance of GHGE from different processes.

Results and discussion

GHGEI was higher in the rainy (1.32 kg CO₂-eq kg⁻¹ FPCM) than in the dry (0.91 kg CO₂-eq kg⁻¹ FPCM) season (P < 0.05). The between farm variance was 0.025 kg CO₂-eq kg⁻¹ FPCM in both seasons. The within farm variance in the estimate for the single farm mean decreased from 0.69 (1 visit) to 0.027 (26 visits) kg CO₂-eq kg⁻¹ FPCM (rainy season), and from 0.32 to 0.012 kg CO₂-eq kg⁻¹ FPCM (dry season). The within farm variance in the estimate for the population mean was 0.02 (rainy) and 0.01 (dry) kg CO₂-eq kg⁻¹ FPCM (1 visit), and decreased with an increase in farm visits. Forage cultivation was the main source of between farm variance, enteric fermentation the main source of within farm variance.

Conclusions

The estimated GHGEI was significantly higher in the rainy than in the dry season. The main contribution to variability in GHGEI is due to variation between observations from visits to the same farm. This source of variability can be reduced by increasing the number of visits per farm. Estimates for variation within and between farms enable a more informed decision about the data collection procedure.

中文翻译：

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了解印度尼西亚小规模奶牛场温室气体排放估算的可变性

目的

对热带地区小农农场的生命周期评估研究通常使用在某一时刻收集的数据，这可能会妨碍对确切情况的评估。我们通过纵向观察评估了印度尼西亚奶牛场温室气体排放 (GHGE) 的季节性差异，并评估了农场访问次数对单个农场的每公斤牛奶 (GHGEI) 估计温室气体排放 (GHGEI) 和人口的影响吝啬的。

方法

对印度尼西亚西爪哇伦邦地区的 32 个小规模奶牛场进行了 LCA 研究。在 1 年内每 2 个月进行一次农场访问 (FV)：FV1-FV3（雨季）和 FV4-FV6（旱季）。温室气体排放量在农场门口之前的所有过程中都进行了评估，包括上游过程（饲料、肥料、燃料和电力的生产和运输）和农场过程（饲养动物、粪便管理和饲草种植）。我们比较了雨季和旱季生产的每单位脂肪和蛋白质校正奶 (FPCM) 的 GHGE 平均值。我们评估了农场访问次数对估计 GHGEI 方差的影响，以及对来自不同过程的 GHGE 方差的影响。

结果和讨论

GHGEI 在雨季（1.32 kg CO ₂ -eq kg ^-1 FPCM）高于旱季（0.91 kg CO ₂ -eq kg ^-1 FPCM）（P  < 0.05）。两个季节的农场间差异为 0.025 kg CO ₂ -eq kg ^-1 FPCM。单个农场平均值估计中的农场内方差从 0.69（1 次访问）减少到 0.027（26 次访问）kg CO ₂ -eq kg ^-1 FPCM（雨季），从 0.32 减少到 0.012 kg CO ₂ -eq kg ⁻¹ FPCM（旱季）。总体平均值估计中的农场内方差为 0.02（雨天）和 0.01（干燥）kg CO₂ -eq kg ^-1  FPCM（1 次访问），并随着农场访问次数的增加而降低。牧草栽培是场间差异的主要来源，肠道发酵是场内差异的主要来源。

结论

估计的 GHGEI 在雨季明显高于旱季。对 GHGEI 变异性的主要贡献是由于访问同一农场的观察结果之间的差异。可以通过增加每个农场的访问次数来减少这种可变性来源。对农场内部和农场之间差异的估计有助于对数据收集程序做出更明智的决定。