Nutrient Addition to a Subtropical Rangeland: Effects on Animal Productivity, Trophic Efficiency, and Temporal Stability

IF 2.4 3区 环境科学与生态学 Q2 ECOLOGY Rangeland Ecology & Management Pub Date : 2024-07-08 DOI:10.1016/j.rama.2024.05.007
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Abstract

A comprehensive understanding of how native grasslands (rangelands) respond to chronic nutrient addition requires considering interactions with climate variability, water availability in particular, and with stocking rate management. We assessed animal production responses to phosphorus plus nitrogen fertilization sustained over a decade on a highly diverse subtropical grassland. Between 2002 and 2011, paddocks (2 ha) stocked with Hereford heifers received 15 kg P + 50 kg N/ha in April/May, plus 50 kg N/ha in August/September, or were left as unfertilized controls (n = 2). Monthly, independent per-paddock, put-and-take adjustment of stocking rates kept sward height within the 6–12 cm range across all paddocks and years. Herbage production, stocking rate, and liveweight gain per animal (LWGA) and per hectare (LWGH) were measured over the 10 consecutive one-year cycles. Fertilization increased LWGH (+53%) because it increased both herbage production (+32%) and liveweight production per unit produced herbage (trophic efficiency +29%). Such higher trophic efficiency was not a direct effect but a consequence of the increased grazing intensity brought about by the 48% higher stocking rate required to maintain target sward heights in fertilized paddocks, especially in winter and spring. Fertilization increased LWGH substantially more in years with higher summer precipitation. Considering that nutrients were added in autumn–winter, greater responses in wetter summers suggest active excreta-driven nutrient recycling between the sequential growth of cool- and warm-season species. Nutrient addition did not decrease temporal stability of herbage production, LWGA or LWGH. A stocking rate management that precluded fertilized paddocks from becoming taller than unfertilized controls, hence mitigating competition for light, could be the reason underlying this unexpected result. By disentangling intrinsic effects of fertilizers from grazing regime-mediated effects, this study helps understand how extensive animal production (agroeco) systems reliant on highly diverse rangelands respond to progressive nutrient enrichment.

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亚热带牧场的养分添加:对动物生产力、营养效率和时间稳定性的影响
要全面了解原生草地(牧场)如何对长期养分添加做出反应,需要考虑与气候变异、特别是水供应以及放养率管理之间的相互作用。我们在一片高度多样化的亚热带草地上评估了动物生产对磷肥和氮肥持续十年的反应。2002 年至 2011 年间,饲养赫里福德小母牛的围场(2 公顷)在 4 月/5 月和 8 月/9 月分别施肥 15 千克磷 + 50 千克氮/公顷和 50 千克氮/公顷,或作为未施肥对照(n = 2)。在所有围场和年份中,每月对每个围场的放养率进行独立的随放随收调整,使草丛高度保持在 6-12 厘米的范围内。在连续 10 个一年周期内,对垃圾产量、放养率、每头牲畜(LWGA)和每公顷(LWGH)的活体增重进行了测量。施肥提高了每公顷活重增重(+53%),因为施肥提高了草料产量(+32%)和单位草料的活重产量(营养效率+29%)。营养效率的提高并不是直接的效果,而是放牧强度增加的结果,因为在施肥的围场中,尤其是在冬季和春季,为了保持目标草丛高度,放牧率需要提高 48%。在夏季降水量较高的年份,施肥会显著增加LWGH。考虑到养分是在秋冬季添加的,较湿润的夏季会有更大的反应,这表明在冷季和暖季物种依次生长的过程中,排泄物驱动的养分循环非常活跃。添加养分并没有降低草料产量、LWGA 或 LWGH 的时间稳定性。施肥后的围场不会比未施肥的对照围场长得更高,从而减少了对光照的竞争,这可能是造成这一意外结果的原因。通过将肥料的内在效应与放牧制度的媒介效应区分开来,本研究有助于了解依赖于高度多样化牧场的大规模畜牧生产(农业生态)系统如何对逐步养分富集做出反应。
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来源期刊
Rangeland Ecology & Management
Rangeland Ecology & Management 农林科学-环境科学
CiteScore
4.60
自引率
13.00%
发文量
87
审稿时长
12-24 weeks
期刊介绍: Rangeland Ecology & Management publishes all topics-including ecology, management, socioeconomic and policy-pertaining to global rangelands. The journal''s mission is to inform academics, ecosystem managers and policy makers of science-based information to promote sound rangeland stewardship. Author submissions are published in five manuscript categories: original research papers, high-profile forum topics, concept syntheses, as well as research and technical notes. Rangelands represent approximately 50% of the Earth''s land area and provision multiple ecosystem services for large human populations. This expansive and diverse land area functions as coupled human-ecological systems. Knowledge of both social and biophysical system components and their interactions represent the foundation for informed rangeland stewardship. Rangeland Ecology & Management uniquely integrates information from multiple system components to address current and pending challenges confronting global rangelands.
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