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Although contour hedgerows are widely advocated to sustain food crop production in cereal-based farming systems in the tropics, little is known about the nutrient dynamics of these systems or the spatial gradients in soil fertility that may develop in the terraces that evolve behind the vegetative barriers. We studied the effects on soil chemical properties of four contour hedgerow systems: double rows of a tree legume Gliricidia sepium (Jacq.) (G); a row of G. sepium and a row of a native pasture grass Paspalum conjugatum (GPas); a row of G. sepium and a row of a productive fodder grass Penisetum purpureum (napier grass) (GPen); and a double row of P. purpureum (Pen). An open-field control (C) without hedgerows was included. The research was conducted in Mindanao, the Philippines on two Oxisols (Ferralsols) with slopes ranging from 20% to 30%; average alley width was 4.7 m and the average hedgerow width was 0.8 m. The prunings of Gliricidia were mulched on the alley (food-crop planting) area, the clippings of Penisetum were removed from the plots, and no pruning was done for Paspalum. Crop residues were distributed uniformly on the alley area as mulch. Each of the two crops in the rotation, rice (Oryza sativa L.) and corn (Zea mays L.), received 20 kg ha ˇ1 each of P and K and 60 kg ha ˇ1 of N. After 4 years of experimentation exchangeable Mg was about 40% lower in the Pen treatment compared to that in the C treatment. There was a tendency for the Pen treatment to have the lowest exchangeable K, Ca, and Mg and Bray-2 extractable P. Exchangeable Ca and Bray-2 P increased while exchangeable Al decreased linearly with a decrease in soil elevation in the alleyways in the hedgerow treatments, although these gradients were not always significant at the pa 0.05 level. Exchangeable K decreased linearly with the decrease in the soil elevation in the Pen treatment (pa 0.12). The use of Penisetum grass as hedgerow crop and at the same time for supplying fodder, mined the soil nutrients indicating that the system is unsustainable unless accompanied by fertilization or manuring. # 1999 Published by Elsevier Science B.V. All rights reserved.

Hedgerows planted along the contour on steep lands in the humid tropics reduce soil erosion and build terraces over time. The objectives of this study in two Hapludoxes in the Philippines were to evaluate changes after 4 years in soil properties and soil water relations on transects perpendicular to the cropped alleys between four grass and tree hedgerow systems and a control. Hedgerow plants included Gliricidia sepium, Paspalum conjugatum , and Penisetum purpureum . Soil properties evaluated as a function of position in the alley (upper, middle, or lower elevation in an alley) included bulk density, mechanical impedance, soil water transmissivity, water retention, soil water pressure, and soil water content. In general, soil properties were not affected by hedgerow system, but were affected by position in the alley. Nearness to the hedgerow, but not hedgerow species, affected soil water distribution ( P = 0.05). Plant available water at the 10–15 cm depth was 0.16 m 3 m −3 , 0.13 m 3 m −3 , and 0.08 m 3 m −3 for the lower, middle, and upper alley position, respectively. Water transmissivity decreased from 0.49 mm s −1 in the lower alley to 0.12 mm s −1 in the upper alley. The lower soil water contents and soil water pressures in and near the hedgerows confirmed competition for water between the hedgerow species and the food crop in the alley, a condition that is expected to suppress food crop production.

Large areas of the world's bunded rainfed lowland ricelands could be planted to a pre-rice crop if waterlogging damage during the early wet season is prevented. To build understanding necessary to develop effective field drainage practices for pre-rice crops, pot and field studies were undertaken on a Typic Tropaquept lowland rice soil in the Cagayan Valley, Philippines. The objective of the studies was to quantify effects of excessive moisture on mungbeans ( Vigna radiata (L.) Wilczek) encountering variable regimes of duration and elevation of water table height in the root zone during a shortterm waterlogging event. Small differences in level and duration of the root zone water table markedly affected plant performance. Yields were reduced by 40–100% when the water table level reached the soil surface for 6 days compared with the unstressed treatment, but were reduced by only 12–17% when the water level was 5 cm below the surface for the same time period. Regression analysis revealed a 4% reduction in yield per centimetre increase in water table level between 5 cm below to 5 cm above the soil surface during the vegetative stage, and a 6.5% reduction per centimetre during the reproductive stage. Field experiments evaluated two prospective surface drainage techniques that farmers could employ to elevate the crop above the zone of saturation during waterlogging events. Planting in furrows, and subsequently hilling up (HU) to create ridges was unsuccessful in improving plant performance (as the base of the plant was not elevated). Planting on 25 cm high ridges formed by a plow dramatically improved growth and yield of mungbean ( ≥ 360% advantage compared with the other treatments) when subjected to a range of waterlogging stress events. Standing water occurred for 5–7 days on the soil surface of HU, broadcast seeded (B), and drilled (D) treatments, but was 56 6 cbelow the base of the plants in the ridge treatment during the two flooding events. The ridging method was observed to be effective for farm-scale use in cultivating pre-rice mungbeans with either animal or tractor power.

Water deficits result in large yield reductions on the one-half of the world's rice land that is rainfed. The most severe water deficits tend to occur during the reproductive stage. Field studies were conducted over a three-year period to develop a method to screen rices for reproductive-phase drought stress resistance. Staggered planting date was effective in synchronizing the flowering of test entries during the stress treatment period. Grain yield, relative grain yield, and spikelet fertility were significantly and negatively related to the number of days beyond the beginning of the stress period that a cultivar flowered. A drought index based on the deviation of entry performance from regression of the plant character on flowering date (expressed as days from application of the drought stress treatment) was used to adjust cultivar performance. Rankings were similar for the index values of the grain yield, relative grain yield, and spikelet fertility. Percent spikelet fertility was highly correlated with grain yield in the event of reproductive-stage water stress ( r 2 = 0.64 ∗∗ , 0.84 ∗∗ and 0.66 ∗∗ during three years of tests). Spikelet fertility was judged the most practical character by which to score cultivar performance. A mass screening method is proposed that involves staggered planting, interruption of irrigation during the flowering period, visual scoring for spikelet fertility, and regression analysis to adjust for differences in flowering date.

Cowpea [ Vigna unguiculata (L.) Walp] is grown widely as an inexpensive source of protein in tropical regions. Production is often limited by either waterlogged or dry soils in the wet-dry transition period following rice because periodically saturated soils are followed by progressively severe drought. An optimum fit of cultivar phenology to these situations is crucial to higher, stable yields. The responses of a set of diverse cowpea differing in maturity were compared under a line-source moisture gradient applied during the vegetative stage on isohyperthermic, clayey, Typic Tropudalf with a fluctuating shallow water table, during two dry seasons in the Philippines. In 1986–1987, in saturated soil, the mean yields of the medium-maturing grain (460 kg ha −1 ) and dual-purpose (460 kg ha −1 ) types exceeded yield of the early-maturing grain (250 kg ha −1 ) and vegetable (210 kg ha −1 ) types, with a similar ranking (920, 730, 470, and 390 kg ha −1 ) without irrigation. In 1988, the medium-maturing cultivar group had a mean yield 985 kg ha −1 in saturated soil and 1389 kg ha −1 in unirrigated, again exceeding the early-maturity group with yields of 544 and 985 kg ha −1 , respectively. Saturated soil reduced seed yields by 10 to 71% in 1986–1987 and 10 to 42% in 1988. Pods per plant, seeds per pod, and individual seed mass of the cultivars were reduced 13 to 32%, 12 to 19%, and 3 to 12%, respectively. The results suggest that the best medium-maturing cultivars had superior adaptation to that of the best early-maturing cultivars in a post-rice environment with prolonged high rainfall and a high water table. Contrasting results are expected in post-rice niches with a deep water table and limited soil water reserves.

There is potential in tropical regions to include cowpea ( Vigna unguiculata (L.) Walp.) in rice ( Oryza sativa ) based cropping systems, especially during the post-monsoonal dry season. The plant water relations, and root and shoot growth of two cowpea cultivars (IT82D-889, early maturing, and TVX1948-012F, medium maturing) were compared in saturated and drier soil moisture regimes on an isohyperthermic, clayey, Typic Tropudalf soil by using a line-source sprinkler differential irrigation system. Saturated soil reduced total dry matter accumulation, plant height, crop growth rate and leaf area index by 20 to 50%, 7 to 10%, 20 to 50% and 20 to 30%, respectively. Root length density (RLD) measurements showed that in saturated soil, roots of both cultivars were concentrated in the top 0.1 m during the vegetative stage, but in the reproductive stage, grew down to 0.8 m. Leaf water potential (LWP) was higher by 0.3 MPa, and conductances were higher by 5 to 29% in dry than saturated soil. The cultivar TVX1948-012F had greater RLD, conductance and LWP than did with IT82D-889 under saturated conditions. Results suggest that the medium-maturing cultivar is better adapted than the early-maturing to high rainfall and high water table conditions in the post-rice environment. Its shallow rooting under saturated soil conditions enables more effective oxygen uptake in the vegetative growth phase. Deep rooting provides for effective water uptake and increased plant water status under subsequent drought conditions in the reproductive growth phase.

Cowpea sown in tropical monsoon climates is often constrained by soil saturation and a high water table during growth. We hypothesized that a strong interaction exists between cowpea maturity class and the soil water table depth regime experienced during the growing season, and that the occurrence of shallow water table depths in the dry-wet transition period before rice and the rapid decline in water table depth in the wet-dry post-rice period favor early maturing cultlvars. The effects of three water table regimes on the performance of 24 diverse cowpea [ (L.) Walp] cultivars was studied on a Typic Tropudalf toposequence. The water table depths in the shallow (SWT), medium (MWT), and deep (DWT) water table regimes varied between 0.06 to 0.54 m, 0.28 to 0.96 m, and 0.68 to 1.44 m in the 2 yr of dry season (DS) experiments. In the wet season fWS), the three regimes were 0 to 0.27 m, 0.30 to 0.60 m, and 0.55 to 1.05 m. Most of the early maturing cultivars exhibited their best performance in the DWT regime, but the medium maturing cultivars were superior in seed yields in all water table regimes. The mean yields of the early maturing cultivars were reduced by 49% (1986–1987 DS) and 57% (1987–1988 DS) in SWT compared to DWT. They were reduced by 50% in the 1987 wet season. The mean yield reductions for the medium maturing cultivars were 40%, 54%, and 51%, respectively, in SWT compared to DWT. Pods per plant was the yield component most affected by excess moisture. Flowering in the SWT was delayed by 4 vs 5 d (DS) and 5 vs 7 d (WS) between the early and medium maturing cultivar groups, respectively. The superiority of the medium maturing cultivats was consistent among sites with a water table within the root zone for a major portion of the crop season.

Cowpea sown after wetland rice in tropical monsoon climates is frequently subjected to soil saturation and a high water table during early growth. We compared the effects of variation in water table regime on the shoot and root growth, and plant water relations of two medium-maturing (cv. TVX3236-01G and TVX3410-02J) and two early maturing (cv. BS6 and IT82D-889) cowpea [Vigna unquiculata (L.) Walp] cultivars in three water table depth regimes on a Typic Tropudalf toposequence. Our objective was to elucidate the possible mechanisms of differential cultivar adaptation to shallow water table conditions [...]

There is potential in cultivating cowpeas (Vigna unguiculata (L.) Walp.) in rice-based cropping systems in the humid tropics as a source of proteins for humans, forage for ruminants, and for improvement of soil fertility. Seasonal and yearly variability is, however, a major constraint. A statistical stability model and a mechanistic simulation model were used to quantify yield variability of early and medium maturity groups of cowpea cultivars in pre- and post-rice environments at Los Banos, Philippines. Four field experiments, with 24 cultivars in each experiment, were conducted in pre- and post-rice environments, to determine the response of the cultivars to varying moisture and to water table depth regimes, and a stability analysis was performed across the regimes using a statistical model. In the post-rice environment, irrespective of moisture and water table depth regimes, the medium maturing cultivars tended to outyield early maturing cultivars, whereas in the pre-rice environment, early maturity demonstrated a distinct yield advantage. The statistical stability model indicated that medium maturing cultivars performed well in high-yielding environments, whereas in low-yielding environments their yields were comparable with those of early maturing types. However, results of the statistical stability model are limited because of the short time series of basic data. To broaden the analysis, a simulation model of the cowpea crop was calibrated and validated for its performance. Measured and simulated dry weights of crop parts (leaves, stems and pods) and soil moisture contents at 10-cm soil depths throughout the growing season indicated satisfactory performance of the simulation model. Long-term simulation results using the validated model indicate that TVX1948-012F (medium maturity) performs betters (800–2250 kg ha−1) than IT82D-889 (early maturity) (430–1620 kg ha−1) with a fluctuating shallow water table in the post-rice environment, whereas IT82D-889 is superior (80–1150 kg ha−1) to TV1948-012F (30–1150 kg ha−1) in the pre-rice environment. Yields are highest and least variable for the 15 January planting in the post-rice environment, and for the 15 April planting in the pre-rice environment.

Recent studies have shown that the grain yields of corn (Zea mays L.) and wheat (Triticum aestivum L.) are related to the degree of water stress they undergo. The purpose of the study reported here was to establish relationships between crop temperature and the grain yields, phenological development, evapotranspiration rates (ET) and leaf water potential (ψl) of two hybrids of grain sorghum (Sorghum bicolor L. Moench) subjected to varying levels of plant water stress. The study was conducted at the University of Nebraska Sandhills Agricultural Laboratory in 1978 on a Typic Ustipsamment (Valentine fine sand) soil. The sorghum hybrids used were RS 626 and NB 505. Four irrigation treatments were applied in order to subject the crops to varying levels of water stress during each of three major growth stages. Soil moisture was monitored with a neutron probe. ET was estimated with the water balance technique. Crop temperature was measured with an IR thermometer and leaf water potential was measured with a Scholander pressure bomb. Grain yields were reduced by water stress occuring at anytime during the growing season. Yield reductions were largest when stress occurred during only the grainfill period and were least when stress occurred during the entire growing season. The percentage reduction in sorghum grain yield can be described by an index involving the seasonal accumulation of the daily mid-day temperature differences between well-watered and stressed crops (Σ TSD). As Σ TSD values increased, ET decreased. However, the correlation of ET with Σ TSD was relatively low (R2 = 0.60) probably due to the limited amount of data available for analysis and inaccuracies in the soil water balance method used to estimate ET. The mid-day temperature of well-watered rows ranged between 18.0 and 32.8 °C with a mid-day temperature range of about 0.5 °C between the well-watered rows in various plots for several days following an irrigation. However, in certain instances, the mid-day temperature range increased to 1–2 °C for a few days before irrigation. This suggests that certain of the rows experienced water stress and should have been irrigated earlier. Yield data support that conclusion. Range in crop temperature within a field appeared to be a sensitive indicator of crop water stress in sorghum. No significant difference in the phenological development of sorghum resulted from water stress except in one NB 505 plot in which plants were stressed throughout the entire season. In that plot, the stressed plants lagged in development behind non-stressed plants by approximately ten days. The differences in mid-day leaf water potentials (Δψl) and crop temperatures (ΔT) between stressed and non-stressed vegetation were examined. As ΔT increased up to about 4 °C, Δψl, also increased. Beyond that point, Δψl decreased while ΔT continued to increase. This behavior was attributed to stomatal closure which permitted an increase in ψl of the stressed plants (hence reducing Δψl) even as ΔT continued to increase.