Abstract Pakistan faces significant future challenges to feed a growing population, with 47 % of the populace currently categorised as food insecure and water becoming scarcer. The current rice-wheat (RW) cropping system is critical for food security, but exhibits low productivity due to sub-optimal varieties, timings, and nitrogen (N) stress. We investigated farmer management strategies to increase the productivity of the RW system while quantifying trade-offs with environmental sustainability (particularly nitrate leaching). Cropping systems simulation with a validated model (APSIM) enabled analysis of a broad range of current management practice modifications (crop sowing dates, varieties, fertiliser rates, and deficit irrigation strategies) in a large Monte-Carlo Matrix (13,000+ elements). We evaluated annual crop production, gross margins (GMs), irrigated water productivity (WPi), nitrate leaching, ET and the crop transpiration proportion of total ET, for all combinations on an annual basis over a 35-year simulation period (1980−2014). We found that WPi in both the highest (Gujranwala) and lowest yielding (Narowal) districts of Punjab can be maximised by using a shorter-season rice cultivar sown slightly later than current farmer practice and irrigated under alternate wetting-and-drying (AWD – with 2–4 days gap), with increased N fertiliser. The currently-used wheat variety was found to be satisfactory and capable of capitalising on the earlier sowing possible through timelier rice harvest, yet with a more generous wheat irrigation strategy (4−5 irrigations rather than 3−4) and N fertiliser regime. The currently-used long-season rice variety maximises GM at Gujranwala, largely due to premium grain prices for that variety, however in this water-limited cropping environment maximising WPi will maximise regional production. If no N-leaching limits apply, system WPi at Gujranwala can be increased by a factor of 2.67x over current farmer levels, via the indicated management changes, with associated N fertiliser increases of 1.8–2.2 times at Gujranwala. If annual N leaching limits are imposed (50, 100 or 150 kg N ha−1), those achievable WPi gains change to 2.0x, 2.6x, and 2.67x respectively at Gujranwala, with limits on applied N fertiliser being the only changes in optimised agronomic management. A key finding was that even under the strictest N-leaching limit (50 kg N ha−1 yr−1, which is similar to what farmers currently lose), it is still possible to significantly increase system water productivity (by 2.0x) through the optimised agronomic changes, while using less fertiliser N (0.8x). Our research indicates considerable gains in rice and wheat food production are possible for the Pakistani Punjab through farmer management changes, however risks associated with uncertain water supplies need to be assessed.

中文翻译：

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调整巴基斯坦旁遮普省的水稻-小麦管理，以在硝酸盐浸出限度内最大限度地提高生产力

摘要 巴基斯坦在养活不断增长的人口方面面临着重大的未来挑战，目前有 47% 的人口被归类为粮食不安全和水资源短缺。当前的稻麦 (RW) 种植系统对粮食安全至关重要，但由于品种、时间和氮 (N) 压力不够理想，生产力低下。我们调查了农民管理策略，以提高 RW 系统的生产力，同时量化与环境可持续性（尤其是硝酸盐浸出）的权衡。使用经过验证的模型 (APSIM) 进行的种植系统模拟能够在大型蒙特卡罗矩阵（13,000 多个元素）中分析当前管理实践的广泛修改（作物播种日期、品种、施肥率和灌溉不足策略）。我们评估了一年的作物产量，在 35 年模拟期（1980-2014 年）中，所有组合的毛利率 (GMs)、灌溉水生产力 (WPi)、硝酸盐浸出、ET 和作物蒸腾占总 ET 的比例。我们发现旁遮普省最高（Gujranwala）和最低产量（Narowal）地区的 WPi 可以通过使用比当前农民种植略晚的短季水稻品种来最大化，并在交替干湿交替（AWD –间隔 2-4 天），增加施氮肥。发现目前使用的小麦品种是令人满意的，并且能够通过更及时的水稻收获利用更早的播种，但具有更慷慨的小麦灌溉策略（4-5 次灌溉而不是 3-4 次灌溉）和氮肥制度。目前使用的长季稻品种最大限度地提高了古吉兰瓦拉的转基因，主要是由于该品种的谷物价格高，但在这种水资源有限的种植环境中，最大限度地提高 WPi 将最大限度地提高区域产量。如果不适用 N 浸出限制，Gujranwala 的系统 WPi 可以比当前农民水平提高 2.67 倍，通过指示的管理变化，Gujranwala 的相关氮肥增加 1.8-2.2 倍。如果施加年度 N 浸出限制（50、100 或 150 kg N ha-1），那么在 Gujranwala 可实现的 WPi 增益分别变为 2.0x、2.6x 和 2.67x，施氮肥的限制是唯一的变化优化农艺管理。一个关键发现是，即使在最严格的 N 浸出限制（50 kg N ha−1 yr−1，这与农民目前的损失相似）下，通过优化的农艺变化，仍然有可能显着提高系统水生产率（2.0 倍），同时使用更少的氮肥（0.8 倍）。我们的研究表明，通过农民管理变革，巴基斯坦旁遮普邦的稻米和小麦粮食产量有可能大幅增加，但需要评估与不确定供水相关的风险。