Nutrient Runoff Potential from Fescue Pastures using Simulated Rotational Grazing of Lactating Dairy Cows

This study was designed to evaluate phosphorus (P) losses from rotationally grazed pastures. Sod of tall fescue was transplanted into boxes 100×18.4 cm². Treatments (13) imposed in triplicate were a no P control, inorganic P at rotational requirements, inorganic P at seasonal requirements, and 10 plots representing a paddock in a 20‐day, alternate‐day grazing rotation. Treatments were isonitrogenous; three rotations were conducted. Inorganic fertilizers were applied on day 1 of the rotation. Dairy slurry from grazing cows was applied daily to the respective treatments. Rainfall was simulated after each rotation, and continuous runoff was collected for 30 min. Total and dissolved reactive P in runoff were lower from control than from P‐amended treatments. No differences were observed among P‐amended plots. The small size of the boxes and naturally high variability in fescue sod did not allow for an accurate assessment of the risk of P losses from rotationally grazed pasture.     

The effects of offering a range of forage and concentrate supplements on milk production and dry matter intake of grazing dairy cows

An experiment was undertaken to examine the effect of supplement type on herbage intake, total dry matter (DM) intake, animal performance and nitrogen utilization with grazing dairy cows. Twenty‐four spring‐calving dairy cows were allocated to one of six treatments in a partially balanced changeover design with five periods of four weeks. The six treatments were no supplement (NONE), or supplementation with either grass silage (GS), whole‐crop wheat silage (WS), maize silage (MS), rapidly degradable concentrate (RC) or slowly degradable concentrate (SC). Cows were rotationally grazed with a mean herbage allowance of 20·5 kg DM per cow per day, measured above 4 cm. Forage supplements were offered for approximately 2 h immediately after each morning milking, with cows on NONE, RC and SC treatments returning to the grazing paddock immediately after milking. Cows on treatment MS had a significantly higher supplement DM intake than the other treatments but a significantly lower grass DM intake than the other treatments, resulting in no significant difference in total DM intake when compared with cows on treatments WS, RC and SC. Concentrate type had no significant effect on herbage intake, milk yield, milk composition or yield of milk components. The yield of milk fat and milk protein was significantly higher on treatments MS, RC and SC compared with treatments NONE, GS and WS. The results indicate that despite a relatively high substitution rate, maize silage can be a useful supplement for the grazing dairy cow.     

Diet selection of dry and lactating beef cows grazing extensive pastures in late autumn

The diet selection, made by twelve dry and twelve lactating spring‐calving Salers beef cows at the end of the grazing season on an extensively grazed natural mountain pasture in central France, was compared. Sward structure, selection bites, daily grazing time and digestibility of the diet were measured in mid‐October (P₁) and mid‐November (P₂). Live weights were measured twice monthly throughout the experiment. Daily milk production was assessed in the week before the grazing behaviour measurements. Lactating cows grazed more selectively than dry cows: they took more bites on green patches (0·20 vs. 0·13 of total bites, P < 0·01; Jacob's selectivity index: 0·13 vs. ?0·25, P < 0·001), which is consistent with the higher overall nitrogen concentration in faeces (18·1 vs. 17·3 g kg^?1 DM, P < 0·05). Lactating cows tended to slightly increase their daily grazing time compared with dry cows (on average 9·9 vs. 9·5 h, P = 0·07) and grazed faster in mid‐November (74 vs. 69 bites min^?1, P < 0·05). The lactating cows lost more live weight (?24 vs. ?12 kg cow^?1, P < 0·05) between P₁ and P₂. A positive correlation was found between consumption of green patches by lactating cows and their daily milk production in P₂ (r = 0·574, P = 0·05), whereas no correlation occurred between individual milk production and liveweight loss. Dry cows were less selective, which supports management practices that promote the use of cows with low requirements on extensively grazed pastures in late season.     

The conservation management of upland hay meadows in Britain: a review

Upland hay meadows conforming to MG3 in the National Vegetation Classification of the UK are a rare habitat in Britain and are largely confined to upland valleys in northern England. Agricultural intensification, particularly ploughing and reseeding and a shift from hay‐making to silage production over the last 50 years, has resulted in large losses of species‐rich upland hay meadows. Remaining species‐rich meadows have been the focus of much nature conservation effort resulting in many of the species‐rich sites being protected by statutory designations or through voluntary agri‐environment scheme agreements. Research and monitoring has tended to confirm that species richness is maximized by management involving spring and autumn grazing, a mid‐July hay cut, no inorganic fertilizer and possibly low levels of farmyard manure. Deviations from this regime result in a loss of species richness. Restoration of semi‐improved grassland to swards resembling species‐rich MG3 also requires a similar regime but is also dependent on the introduction of seed of appropriate species. The role of Rhinanthus minor as a tool for manipulating meadow biodiversity during restoration management is discussed. Suggestions for future research are outlined.     

Performance and environmental effects of forage production on sandy soils. II. Impact of defoliation system and nitrogen input on nitrate leaching losses

A field experiment was conducted over a 4‐year period to determine NO₃ leaching losses from grassland on a freely draining sandy soil. The experiment consisted of all combinations of five defoliation systems; cutting‐only (CO), rotational grazing (GO), mixed systems with one (MSI) or two silage cuts (MSII) plus subsequent rotational grazing, and simulated grazing (SG), four mineral nitrogen (N) application rates (0, 100, 200, and 300 kg N ha^?1 year^?1), and two slurry levels (0 and 20 m³ slurry ha^?1 year^?1). Due to the high N return by grazing animals, leaching losses in the rotational grazing systems generally were associated with NO₃‐N concentrations which exceeded the EU limit for drinking water. NO₃ leaching losses in a rotational grazing system could be reduced by lowering the N fertilizer intensity and the inclusion of one or two silage cuts in spring. However, even in the unfertilized mixed systems, N fixation by white clover exceeded the amounts of N removed via animal products, which resulted in NO₃‐N concentrations well above the EU limit for drinking water. In terms of leaching losses, the cutting‐only system was the most advantageous treatment. NO₃ leaching losses on grassland could be predicted by the amount of soil mineral N at the end of the growing season and by the N surplus calculated from N balances at the field scale. From the results obtained a revised nitrogen fertilization policy and a reduced grazing intensity by integrating silage cuts are suggested.     

Selective defoliation by sheep according to slope and plant species in the hill country of New Zealand

The objective of the study was to evaluate the grazing behaviour by sheep in hill country paddocks in New Zealand which had received two long‐term fertilization and stocking rate treatments [high fertility–high stocking rate (HH); low fertility–low stocking rate (LL)]. Herbage accumulation and selective grazing were evaluated within low slope (LS), medium slope (MS) and high slope (HS) categories. Transects lines were placed and tillers of Agrostis capillaris and Lolium perenne in the LS category; A. capillaris, Anthoxanthum odoratum and L. perenne in the MS category; and A. capillaris and A. odoratum in the HS category were marked. The leaf length of each marked tiller was measured and used to determine selective grazing over 3 weeks during each season. The highest herbage accumulation rates were during spring and the lowest in summer and winter. The LS category showed the highest herbage accumulation rates and HS the lowest. Except for autumn, the marked tillers were more frequently grazed in the HH than in the LL paddock. During summer, autumn and spring, grazing frequency in the slope categories was in the order LS > MS > HS. During winter sheep did not discriminate between slope category. During summer, autumn and spring, sheep did not selectively graze the species studied but this was not the case during winter. Overall, sheep selectively grazed L. perenne. In all the seasons L. perenne consistently had the longest leaves but within species there was no consistent relationship between leaf length and probability of being grazed. Selective grazing changed through the year according to herbage accumulation rate. Sheep concentrated grazing in the category LS when herbage accumulation rate was high, but they did not discriminate between slope categories in winter when herbage accumulation rate was low.     

土地利用和管理方式对农牧交错带土壤碳密度的影响

为研究农牧交错区土地利用和管理方式对土壤碳库的影响,以农牧交错区未扰动自然土壤的天然草地和扰动自然土壤的开垦农田为研究对象,测定了不同土地利用和管理方式下0～50 cm土层的土壤体积质量、土壤有机碳含量及土壤有机碳密度。结果表明,5种土地利用和管理方式下的土壤有机碳密度在8.21～11.30 kg/m2之间,土壤有机碳主要分布在土壤表层,随着土层深度增加,土壤有机碳含量和密度减小。未扰动自然土壤的天然草地,0～50 cm的土壤有机碳含量及碳密度高于扰动自然土壤的开垦农田及撂荒地,以草地围封刈割利用下的土壤有机碳密度最高,草地自由放牧利用下的土壤有机碳密度最低。扰动自然土壤的农田撂荒10 a后与开垦农田相比,0～50 cm土层的有机碳含量及碳密度显著提高。土地利用及管理方式的变化改变了土壤体积质量及土壤有机碳含量,进而影响了土壤有机碳密度。围封割草或控制放牧,是适宜农牧交错区增加生态系统土壤碳贮量的利用途径。     

季节放牧对典型草原植物群落不同生长季特征的影响

在内蒙古典型草原区建立放牧试验平台,研究秋季、冬季和初春放牧对草地植物返青期土壤温湿环境和植物生长以及生长旺季植物群落地上生物量及其构成的影响。结果表明:在草地返青季,秋季放牧草地表层土壤湿度相对于其他处理显著降低,而温度相对升高;土壤表层湿度与草地枯落物总量、立枯量呈显著正相关;秋季和冬季放牧显著降低草地返青期的地上生物量;秋季放牧显著降低优势植物地上生物量;而初春放牧不影响草地返青期的群落生物量。在生长旺季,初春放牧草地群落及其高大优势植物大针茅和羊草的生物量显著增加,而其下层的糙隐子草和杂类草生物量显著减少。     

放牧强度季节调控对荒漠草原土壤风蚀的影响

由超载过牧导致的草地退化是土壤沙化的重要来源,放牧导致的草地风蚀加剧和草地沙化现象已经引起人们的普遍关注。以短花针茅荒漠草原为研究对象,采用完全随机区组设计设置6个放牧处理,对不同放牧处理下草地枯落物生物量、冬春季集沙量及土壤表层粒径等进行研究。结果表明:1)冬春季草地保存枯落物生物量越多,草地的固沙能力越强,适度放牧草地流沙量比重度放牧降低了45.16%;2)随着放牧强度的增大,草地不同粒径流沙量绝对值明显增加,>0.25 mm和<0.05 mm粒径沙粒的比例在重度放牧下较不放牧和轻度放牧高,0.25~0.10 mm粒径沙粒在重度放牧下最低;3)秋季重度放牧能增加草地流沙量,因此荒漠草原放牧利用在秋季应降低载畜率。所以,草地不合理的放牧利用降低了草地防风固沙能力,导致地表粗粒化,荒漠草原冬春季保持不少于32.93 g·m^-2的枯落物,能显著降低草地风蚀,起到很好的固沙作用。     

返青期休牧对退化高寒草甸植被生长及其优势植物垂穗披碱草光合作用的影响

返青期休牧为退化草地恢复中最经济可行的措施且已得到了较广泛的推广和应用,为探索返青期休牧对高寒草地植物生长及光合特性的影响,本研究于2015年开始在青海省祁连山区进行返青期休牧试验,于2018年和2019年调查并测定试验样地植物群落特征和光合生理指标。结果表明：返青期休牧4年后,草地总盖度、优势种牧草垂穗披碱草（Elymus nutans）高度、地上生物量和地下生物量较未休牧分别提高了35%,777%,1140%和217%,垂穗披碱草叶绿素含量和净光合速率分别增加了172%和146%;草地总盖度、地上生物量和垂穗披碱草叶绿素含量及净光合速率在休牧第4年和休牧第5年之间差异不显著。因此,在高寒草地实施返青期休牧可提高优势牧草光合作用、促进退化草地植被的恢复,且退化草地植被在休牧一定年限后趋于稳定。本研究为青藏高原推广实施返青期休牧这一措施来恢复退化草地植被提供了理论基础。