Institute at Brown for Environment &Society, Brown University, Providence, Rhode Island 02912, USA.
Rubenstein School of Environment and Natural Resources, University of Vermont, Burlington, Vermont 05405, USA.
Nat Plants. 2016 Apr 18;2(5):16043. doi: 10.1038/nplants.2016.43.
Agricultural intensification in the tropics is one way to meet rising global food demand in coming decades(1,2). Although this strategy can potentially spare land from conversion to agriculture(3), it relies on large material inputs. Here we quantify one such material cost, the phosphorus fertilizer required to intensify global crop production atop phosphorus-fixing soils and achieve yields similar to productive temperate agriculture. Phosphorus-fixing soils occur mainly in the tropics, and render added phosphorus less available to crops(4,5). We estimate that intensification of the 8-12% of global croplands overlying phosphorus-fixing soils in 2005 would require 1-4 Tg P yr(-1) to overcome phosphorus fixation, equivalent to 8-25% of global inorganic phosphorus fertilizer consumption that year. This imposed phosphorus 'tax' is in addition to phosphorus added to soils and subsequently harvested in crops, and doubles (2-7 Tg P yr(-1)) for scenarios of cropland extent in 2050(6). Our estimates are informed by local-, state- and national-scale investigations in Brazil, where, more than any other tropical country, low-yielding agriculture has been replaced by intensive production. In the 11 major Brazilian agricultural states, the surplus of added inorganic fertilizer phosphorus retained by soils post harvest is strongly correlated with the fraction of cropland overlying phosphorus-fixing soils (r(2) = 0.84, p < 0.001). Our interviews with 49 farmers in the Brazilian state of Mato Grosso, which produces 8% of the world's soybeans mostly on phosphorus-fixing soils, suggest this phosphorus surplus is required even after three decades of high phosphorus inputs. Our findings in Brazil highlight the need for better understanding of long-term soil phosphorus fixation elsewhere in the tropics. Strategies beyond liming, which is currently widespread in Brazil, are needed to reduce phosphorus retention by phosphorus-fixing soils to better manage the Earth's finite phosphate rock supplies and move towards more sustainable agricultural production.
在热带地区加强农业是未来几十年满足全球粮食需求增长的一种方式（1,2）。虽然这种策略可以使土地免于转为农业用途（3），但它依赖于大量的物质投入。在这里，我们量化了这样一种物质成本，即在固磷土壤上强化全球作物生产并实现与高生产力温带农业相似的产量所需的磷化肥。固磷土壤主要出现在热带地区，使作物吸收的磷减少（4,5）。我们估计，在 2005 年，要使全球覆盖固磷土壤的 8-12%的农田集约化，需要每年 1-4 百万吨磷来克服磷固定，相当于当年全球无机磷肥消耗的 8-25%。与施入土壤后被作物吸收的磷相比，这种强加的磷“税”是额外的，而在 2050 年的耕地面积情景中，这一数字翻了一番（2-7 百万吨磷/年）（6）。我们的估计是基于巴西的地方、州和国家规模的调查得出的，在巴西，与任何其他热带国家相比，低产农业已经被集约化生产所取代。在巴西的 11 个主要农业州，收获后土壤中保留的无机化肥磷的盈余与覆盖固磷土壤的耕地面积比例呈强相关（r²=0.84，p<0.001）。我们对巴西马托格罗索州的 49 位农民进行的采访表明，即使在三十年的高磷投入之后，也需要这种磷盈余，该州生产的大豆占全球大豆产量的 8%，主要种植在固磷土壤上。我们在巴西的研究结果强调了需要更好地了解热带地区其他地区长期土壤磷固定的情况。除了石灰化之外，还需要其他策略来减少固磷土壤对磷的保留，以更好地管理地球上有限的磷矿资源，并朝着更可持续的农业生产方向发展。
