The effect of toposequence position on soil properties,hydrology, and yield of rainfed lowland rice in Southeast Asia

A large proportion of rainfed lowland rice in Southeast Asia is grown in gently sloping areas along toposequences with differences in elevation of a few meters. These small differences in elevation can lead to differentiation in soil properties and hydrological conditions, which in turn may affect crop performance and yield. It may be appropriate to replace blanket crop management recommendations in rainfed areas with toposequence-specific management recommendations. However, thorough statistical analyses of the relationships between toposequence position and field and crop conditions are lacking. In this paper, we statistically analysed the effect of toposequence position on soil properties, hydrological conditions, yield, and yield increase due to weed control and/or fertilizer management in rainfed areas in four villages in Indonesia and Thailand each in 2000–2002.     

Subcutaneous tissue discoloration in ware potatoes. 2. Impact measured by an instrumented sphere

Summary Potatoes are exposed to mechanical forces which can lead to subcutaneous tissue discoloration resulting in losses. We investigated the number and intensity of impacts in different phases of representative Dutch ware potato handling chains using an instrumented sphere (IS). Other questions we asked were, to which drop height onto a defined surface do measured impacts correspond, and what is the relation between the number of impacts and damage? Close relationships between peak acceleration and velocity change for different drop heights were found for various cushioning materials, thus allowing interpretation of impact measurements in terms of drops. The IS recorded c. 340 impacts exceeding 30g. The contribution to the total number of impacts was 11% for Harvest, 0% for Storage, 10% for Transport and 79% for Packaging. The number and intensity of impacts correlated well with the amount of subcutaneous tissue discoloration. It is concluded that the produce-friendliness of the handling chains can be improved.     

华北地区旱稻产量适应性及耗水特征分析

本研究利用2001～2002年的试验结果,分析了北京昌平旱稻的产量及产量构成要素、水分利用效率和耗水特征.结果表明:在水分输入为300～522mm条件下,北京地区"旱稻297"和"早稻502"的产量水平分别为3876～5289kg·hm-2、3977～5664kg·hm-2,灌溉水的水分利用效率分别为1.01～1.29g·kg-1、1.03～1.33g·kg-1,同一品种不同水分处理之间存在差异."早稻502"的产量和水分利用效率均高于"早稻297",表明"早稻502"更适宜在北京地区种植.对产量分析可以看出,在损失7.9%～29.8%产量前提下,水分利用效率可以提高1.9%～27.7%,其中前期限量灌溉处理的水分利用效率提高幅度最大,为3.6%～23.1%,而产量仅降低7.9%～15.5%.表明前期限量后期充分灌溉处理为北京地区气候条件下的早稻节水灌溉模式.同时利用北京地区昌平气象站1951～2005年的气侯资料,分析了旱稻生长季内的降水特点,根据person-Ⅲ分布法确定了早稻生长季内的3种降水年型,并分析了不同降水年型下旱稻生长季内的降水与作物需水的耦合度.结果表明:旱稻在正常年和干旱年型下生长季内各生育阶段均需灌溉水补充,而湿润年型只需在开花～成熟阶段适当补充灌溉.     

Alleviating soil sickness caused by aerobic monocropping: Responses of aerobic rice to nutrient supply

Yield decline is a major constraint in the adoption of monocropping of aerobic rice. The causes of the yield decline in the continuous aerobic rice system are still unknown. The objective of this study was to determine if nutrient application can mitigate the yield decline caused by continuous cropping of aerobic rice. Micro-plot experiment was conducted in 2005 dry season (DS) in a field where aerobic rice has been grown continuously for eight seasons from 2001 DS at the International Rice Research Institute (IRRI) farm. Pot experiments were done with the soil from the same field where the micro-plot experiment was conducted and aerobic rice has been grown continuously for 10 seasons. Apo, an upland rice variety, was grown under aerobic conditions with different nutrient inputs in field and pot experiments. The field micro-plot experiment showed that micronutrients had insignificant effect on plant growth under continuous aerobic rice cultivation but the combination of N, P, and K mitigated the yield decline of continuous aerobic rice. A series of pot experiments studying the individual effects of nutrients indicated that N application improved plant growth under continuous aerobic rice cropping, while P, K, and micronutrients had no effect. Increasing the rate of N application from 0.23 to 0.90 g per pot in the continuous aerobic rice soil increased the vegetative growth parameters, chlorophyll meter readings, and aboveground N uptake consistently. Our results suggested that N deficiency due to poor soil N availability or reduced plant N uptake might cause the yield decline of continuous cropping of aerobic rice.     

Relative effects of ammonia and nitrite on the germination and early growth of aerobic rice

Recent studies have documented adverse affects of urea on the establishment and growth of aerobic rice when applied at seeding. The following experiments were conducted to examine the relative importance of ammonia and nitrite (NO$ _2^- $ ) toxicities as mechanisms contributing to poor germination and early growth of aerobic rice. Soil was collected from an experiment in the Philippines where aerobic rice was grown continuously for 7 years. Subsamples of the soil were: (1) pretreated with sulfuric acid (0.5 M H₂SO₄ added at 75 mL kg^–1), (2) oven‐heated at 120°C for 12 h, or (3) left untreated. In a greenhouse study N was applied to the untreated, acidified, and oven‐heated soils as either urea or ammonium sulfate (0.0 or 0.3 g N kg^–1). Plant height, root length, total biomass, and number of seminal roots were evaluated after 10 d. Microdiffusion incubations were used to assess the effects of soil pretreatment, N source, and N rate (0, 0.5, 1.0, 1.5 g N kg^–1) on ammonia (NH₃) volatilization and germination. Nitrite incubations were conducted to establish a critical level for NO$ _2^- $ toxicity and measure the extractable NO$ _2^- $ and germination trends as affected by soil pretreatment, N source, and N rate. On untreated soil, urea reduced early growth and germination while ammonium sulfate caused no adverse effects. Progressively higher rates of urea increased NH₃ volatilization and inhibited germination, while oven‐heating and acidification minimized the adverse effects. All treatment combinations (soil pretreatment, N source, N rate) had extractable NO$ _2^- $ levels below the critical level of 0.2 g N kg^–1, suggesting that ammonia and not NO$ _2^- $ toxicity was the principal cause of inhibition. Since the risk of NH₃ toxicity is highest just following urea hydrolysis, strategies to optimize the timing and placement of urea should be considered.     

旱稻农田土壤水分变化特征研究

试验研究旱稻不同灌溉处理土壤水分变化特征结果表明，不同供水条件下农田土壤水分变化的主要层次均为80cm以上，120cm以下土层土壤水分处于相对稳定状态，且维持在相对较高水平；供水较多时旱稻水分耗散量、耗水强度也较大，而相同供水条件下旱稻水分耗散量和耗水强度又小于水稻对照；相同灌溉处理旱稻产量和水分利用效率均高于水稻对照；而充足供水有利于旱稻根系在0～20cm表层发育，但不利于其根系在下层生长，而W2可促使根系下扎，更充分利用下层水分。     

华北平原旱稻作物系数试验研究

该文依据2001～2004年4年田间试验资料,利用Penman-Monteith公式计算了北京地区旱稻出苗～成熟期间参考作物蒸散量,并利用农田水量平衡方程及土壤水分胁迫系数计算了作物实际蒸发蒸腾量,由此计算了旱稻各生育阶段的作物系数,并分析了旱稻作物系数变化规律。结果表明：北京地区旱稻出苗～成熟期间参考作物蒸散量平均为560.1 mm;日平均孕穗～开花期最高为6.8 mm/d,年际变化幅度很小。旱稻作物系数全生育期平均为1.07,在孕穗～开花期最大,为1.49,其次为开花～成熟阶段,平均为1.20,拔节～孕穗最小为0.87;在北京气候背景下,旱稻作物系数与出苗后天数和大于0℃积温具有较好的三次多项式关系。     

Yield gap of rainfed rice in farmers’ fields in Central Java, Indonesia

Yield constraint analysis for rainfed rice at a research station gives insight into the relative role of occurring yield-limiting factors. However, soil nutrient status and water conditions along toposequences in rainfed farmers’ fields may differ from those at the research station. Therefore, yield constraints need to be analyzed in farmers’ fields in order to design management strategies to increase yield and yield stability.We applied production ecological concepts to analyze yield-limiting factors (water, N) on rice yields along toposequences in farmers’ fields using data from on-farm experiments conducted in 2000-2002 in Indonesia. Potential, water-limited, and N-limited yields were simulated using the ORYZA2000 crop growth model. Farmers’ fields showed large spatial and temporal variation in hydrology (354-1235 mm seasonal rainfall, −150 to 50 cm field-water depth) and fertilizer doses (76-166 N, 0-45 P, and 0-51 kg K ha⁻¹). Farmers’ yields ranged from 0.32 to 5.88 Mg ha⁻¹. The range in yield gap caused by water limitations was 0-28% and that caused by N limitations 35-63%, with large temporal and spatial variability.The relative limitations of water and N in farmers’ fields varied strongly among villages in rainfed rice areas and toposequence positions, with yield gaps due to water and N at the top and upper middle positions higher than at the lower middle and bottom toposequence positions, and yield gaps in late wet seasons higher than those in early wet seasons. Management options (e.g. crop establishment dates, shortening turnaround time, using varieties with shorter duration, supplemental irrigation) to help the late-season crop escape, or minimize the negative effects of, late-season droughts and supplying adequate N-fertilizer are important for increasing yield in rainfed lowland rice in Indonesia. More N-fertilizer should be given to upper toposequence positions than to lower positions because the former had a lower indigenous nutrient supply and hence a better response to N-fertilizer inputs. Systems approaches using production ecological concepts can be applied in yield constraint analysis for indentifying management strategies to increase yield and yield stability in farmers’ fields in other rainfed lowland areas.     

The effect of green crop lifting on the contamination of seed potato tubers by pathogenicErwinia spp.

Summary In the Netherlands seed potato crops are harvested when still green, the haulm being destroyed before harvest. We compared the effect on the contamination of seed potatoes byErwinia carotovora subsp.atroseptica (Eca) andE. chrysanthemi (Ech) of the common method of haulm destruction by flailing and chemically destroying remaining stems, with the recently developed green crop lifting method. After chenical haulm destruction the levels of contamination with both Eca and Ech surviving cold storage were found not to differ significantly from those after green crop lifting. Losses due to watery wound rot (Pythium ultimum) were considerable in the warm and humid conditions during 1991, especially after green crop lifting.     

Causes for soil sickness affecting early plant growth in aerobic rice

In aerobic rice, adapted varieties are grown in non-flooded and non-saturated soil. In the Philippines, occasional poor crop growth and yield failures have been reported. To investigate the underlying causes, we conducted 3 pot experiments using the aerobic rice variety Apo and so-called “sick soil” from a field where aerobic rice failed in four successive dry seasons. The (experimental) aerobic rice crop replaced the farmer's practice of wet-season lowland rice and dry season sweet potato cropping. We hypothesized that abiotic factors, especially the inter-relationship between high soil pH and impaired micronutrient uptake, restrict plant growth, and that ammonium sulfate has an ameliorating effect. Experiment 1 used “sick soil” collected from around yellowing and dying plants in a field experiment with aerobic rice yield failure, and “healthy soil” collected from around well-growing plants in the same field. We used three N fertilizer treatments (ammonium sulfate, urea, no application) and two soil water conditions (well drained and water-logged). In experiment 2, the treatments were a combination of sick and healthy soil, N fertilizer, soil acidification, and foliar application of Fe. Experiment 3 compared the irrigation water used at the experimental field site with reverse-osmosis water. Irrigation with water from the field site increased soil pH, impaired plant growth, and induced chlorosis. The application of ammonium sulfate reduced soil pH to values below 6 and increased plant micronutrient (Fe, Mn and Zn) contents and plant growth. In early vegetative plant growth, the high soil pH appeared to be the key determinant of “sick soil”, while root knot nematodes were most likely secondary causes for poor plant growth.