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首页> 外文期刊>Crop and Pasture Science >Changes in the acidity and fertility of a red earth soil under wheat–annual pasture rotations
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Changes in the acidity and fertility of a red earth soil under wheat–annual pasture rotations

机译：小麦—牧草轮作条件下红壤土壤酸度和肥力的变化

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摘要

This paper reports the effects of 6 wheat–annual pasture rotations over 18 years on soil N, organic C, P, and pH in a red earth soil at Wagga Wagga (35° 03′ S, 147° 21′E), in southern NSW. There were 3 cropping intensities (33, 50, 67%) with pastures dominated by subterranean clover (Trifolium subterraneum L. cv. Bacchus Marsh) and annual ryegrass (Lolium rigidum Gaud. cv. Wimmera). Rotations were long (6-year) or short (2- or 3-year).nnInitial soil N and organic C concentrations (0–10 cm) were low, 1300–1400 kg N/ha and 0·7–0·9 g organic C/100 g. The rate of increase of total N in the top 20 cm was the same on short and long rotations, and increased with the proportion of pasture in the rotation from 2·0 to 12·1 to 20·7 kg N/ha · year for pasture to crop ratios of 0·33, 0·50, and 0·67. Estimates of the amounts of N fixed and the measured accumulation of N per pasture year varied within the narrow ranges of 95–113 and 45–64 kg N/ha · pasture year. Organic C increased faster as the proportion of pasture in the rotation increased and there was no evidence that steady-state concentrations were achieved by Year 18.nnEstimates of the average amount of N leached below 30 cm varied in the range 22–29 kg N/ha · year. Analysis of the individual crop and pasture effects on soil N in the surface 10 cm indicated that net nitrate leaching was greatest in the second pasture year or in the first crop year following 1 year of pasture. A significant amount of N leached during the first 2 or 3 pasture years in a rotation was recovered by the first wheat crop or by the third and fourth year pastures. Second to fourth cereal crops depleted soil N by an amount similar to that removed in the grain. Average grain N% for the rotation treatments was closely described (R2 = 0·96) as a function of the length of the pasture phase, the pasture to crop ratio, and the interaction pasture to crop ratio number of preceding wheat crops.nnIn the top 30 cm the pH changed at a rate near –0·04 units/year on all treatments, equivalent to addition of 2·3–2·8 kmol H+/ha · year. The acid addition rate, and hence the long-term lime requirement (50 kg lime/kmol H+), did not vary with pasture to crop ratio or with the length of the rotation. The proportion of the acid added to the top 30 cm of soil that was contributed from the N cycle (nitrification followed by nitrate loss by leaching below 30 cm or by run-off) was 0·65 for rotations with 67% pasture and 0·80 for rotations with 33% pasture. Carbon cycle acids, produced during organic matter accumulation and the synthesis of products that were subsequently removed, accounted for the remainder.nnIndividual crop and pasture effects on soil pH were near the overall mean of –0·04 units except in years preceding and following the transition from pasture to cereal phases of the rotations. In cereal-dominated rotations the last pasture year was strongly acid (pH decrease 0·13–0·17) and the following cereal year was alkaline (pH increase 0·05–0·08). In pasture-dominated rotations the effects were reversed, the last pasture being alkaline (pH increase 0·07–0·12) and the following cereal being acid (pH decrease 0·13–0·19). In the 50% rotations, effects were intermediate.nnOrganic and inorganic forms of soil P in the surface 10 cm increased linearly with time, accounting for 38% of the applied fertiliser P. Of the applied P, 88% was accounted for by the sum of P accumulated in the surface 20 cm of soil and by removal in products and waste products. The remainder may have been lost by erosion or accumulated in forms resistant to extraction by 0·1 M H2SO4 after ignition at 550°C. There was a slightly greater rate of increase of organic P as the proportion of pasture in the rotation increased. The annual addition of 11·8 kg P/ha·year marginally exceeded the amount required to maintain the available P concentration.
机译：本文报告了南部南部瓦格瓦格（Wagga Wagga）（35°03′S，147°21′E）的红壤土壤在18年内进行的6次小麦–年度牧场轮换对土壤N，有机碳，磷和pH的影响新南威尔士州。共有3种耕种强度（33％，50％，67％），其中以三叶草（Trifolium subterraneum L. cv。Bacchus Marsh）和一年生黑麦草（Lolium Islamicum Gaud。cv。Wimmera）为主。轮作期较长（6年）或较短（2至3年）。nn初始土壤氮和有机碳浓度（0–10 cm）低，1300–1400 kg N / ha和0·7-0·9克有机碳/ 100克。短期和长期轮作时，顶部20 cm的总氮增加速率相同，并且随着牧场中轮换的比例从2·0增至12·1至20·7 kg N / ha·年而增加牧场与农作物的比例为0·33、0·50和0·67。每个牧场年固定氮的含量估算值和测得的氮累积量在95–113和45–64 kg N / ha·牧场年的狭窄范围内变化。随着牧草在轮作中的比例增加，有机碳的增加更快，并且没有证据表明到18年时达到稳态浓度。nn估计，在30 cm以下浸出的平均N量的估算值范围为22–29 kg N /哈·年。对单个作物和牧场对10 cm表层土壤N的影响的分析表明，硝酸盐的净淋失在牧场第二年或牧场一年后的第一作物年度最大。轮作的前2年或3年中，大量的氮被第一批小麦作物或第三，第四年的牧场回收。第二至第四谷类作物消耗的土壤N量与谷物中去除的氮量相似。轮作处理的平均谷粒N％（R2 = 0·96）被严格描述为牧场期长度，牧场与作物的比率以及先前小麦作物的相互作用牧场与作物的比率数量的函数。在所有处理中，顶部30 cm的pH值均以–0·04单位/年的速度变化，相当于增加2·3–2·8 kmol H + / ha·年。酸的添加速度，以及长期的石灰需求量（50 kg石灰/ kmol H +），不会随草场与作物的比例或轮作时间而变化。 N循环（硝化继而由于在30 cm以下淋溶或流失而导致硝酸盐损失）导致的添加到土壤表层30 cm的酸的比例为60％牧草和0。旋转33％的草场时旋转80。在有机物积累过程中产生的碳循环酸和随后被去除的产物合成中，占了其余部分。nn除pH前后的年份外，个人作物和牧场对土壤pH值的总体平均值接近–0·04个单位。从牧场到轮作的谷物阶段的过渡。在以谷类为主的轮作中，最后一个牧草年是强酸（pH降低0·13–0·17），接下来的谷类是碱性（pH升高0·05-0·08）。在以牧场为主的轮作中，效果相反，最后一个牧场是碱性的（pH升高0·07-0·12），随后的谷物是酸性的（pH降低0·13-0·19）。在50％的轮作中，效果是中等的。nn在表面10 cm处，有机和无机形式的土壤P随着时间线性增加，占施肥P的38％。在施肥P中，88％占总施肥量的磷在土壤20厘米的表面积聚，并通过清除产品和废物而积累。在550°C点火后，剩余物可能因腐蚀而损失或积累为抗0·1 M H2SO4萃取的形式。随着牧草在轮作中的比例增加，有机磷的增加速率略有增加。每年11·8 kg P / ha·年的添加量略微超过了维持有效P浓度所需的量。

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