Intercropping of upland rice (Oryza sativa L.) with short-duration grain legumes has shown promising productivity and resource use efficiency. To better understand intercrop relationships, we used aboveand underground partitions, residue removal, and plant removal to investigate the interactions between upland rice (120-d crop duration) and mungbean [Vigna radiata (L) Wilczek, 65-d crop duration]. Treatments were evaluated during two rainy seasons on an unfertilized Typic Tropudalf at Los Bafios, Philippines. Nitrogen uptake by intercropped rice (33.4 and 41.1 kg N ha1) approximated that of sole rice (35.4 and 38.1 kg N ha1). Intercropped rice yielded 73 to 87% of sole rice and intercropped mungbeans yielded 59 to 99% of sole mungbean. Root barriers did not affect rice N uptake or dry matter accumulation prior to the maturity of the mungbean, but reduced N uptake, dry matter, and grain yields substantially by the time of rice harvest. Sole rice with every third row removed at mungbean harvest had N, grain, and dry matter yields similar to the intercropped rice with every third row occupied by the legume. Sole rice with every third row vacant during the entire growing season yielded similarly (2.6 Mg h1) to sole rice (2.3 Mg h1) and intercropped rice (2.0 Mg h1). There was no evidence that N transfer from the legume to the rice increased N availability to rice above that expected with a sole rice crop with the same planting scheme. Rice yield compensation in the intercrop was apparently due to the increased soil volume for N extraction and increased aerial space available after mungbean harvest.
Tag: oryza sativa
Fallow and sesbania effects on soil nitrogen dynamics in lowland rice-based cropping systems
Vast areas of rice-growing (Oryza sativa L.) lowlands in Asia are fallowed or cropped with non-rice crops for part of the year. Nitrate can accumulate during the fallow or non-rice crop, but this nitrate can be lost upon flooding for rice production. To determine fallow and green manure crop effects on soil nitrate and ammonium dynamics in lowland riceland, a 2-yr field study was conducted in the Philippines. Treatments before wet season rice were (i) Sesbania rostrata grown for either 45 or 60 d, (ii) weedy fallow, and (iii) weed-free fallow. Sesbania rostrata was sown with irrigation in late April-early May, rains started in early (1989) or mid-May (1990). Weeds and S. rostrata were incorporated after soil flooding on 23 June. Rains increased soil water-filled pore space to above 0.75 mL mL1 between mid-May and soil flooding. Weeds and S. rostrata assimilated soil nitrate, as evidenced by lower (P < 0.05) nitrate in those treatments than in the weed-free fallow. The decrease in soil nitrate in the weedfree fallow from 24 April to before soil flooding (15 kg N ha1) was apparently due to denitrification or leaching; additional nitrate (19 kg N ha1 in 1990) disappeared after soil flooding. Ammonium-N was rapidly released from incorporated weeds and S. rostrata. It reached a maximum by 36 d after incorporation, which correlated (r = 0.95) with N accumulation by rice at 45 d after transplanting. Results suggest that weeds and crops before rice can reduce soil N loss by assimilating nitrate-N and then cycling this N through incorporated plant residues back to the soil where it is rapidly mineralized and used by rice.
Rapid yield loss of rice cropped successively in aerobic soil
Upland rice (Oryza sativa L.), commonly considered to be low yielding, can be high yielding if the genotype is improved for harvest index (HI) and the crop is grown relatively free from nutrient and drought stresses. We examined whether high and stable rice yields could be obtained in aerobic soil. In four experiments of 1- to 3-yr duration, lime, N, and P were inputs for wet-season upland rice ‘UPLRi-5’ in a favorable rainfed Oxisol. In a 3-yr experiment consisting of two crops per year in an irrigated Ultisol, different lowland and upland varieties were grown in limed and fertilized aerobic soil. First-season rainfed UPLRi-5 yield varied from 1.5 to 7.4 Mg ha1, with low yields in fields receiving low early-season rainfall. With irrigation, the lowland hybrid ‘Magat’ yielded 7.8 Mg ha1 vs. 2.1 Mg ha1 for traditional upland rice ‘Lubang Red’. Magat’s high yield was associated with a HI of 0.43 in contrast to 0.31 of improved upland rice variety ‘Apo’ and 0.17 of Lubang Red. Whether the crop was rainfed or irrigated, yield loss was rapid following the first season: Grain yields decreased by up to 73% for rainfed UPLRi-5 in the second to third season. In the irrigated upland, yield loss in the second to fourth season was reflected in a 16 to 79% decline in 10-wk biomass. Here, the 13-wk biomass in the fifth crop was only half that of the simultaneously grown first-season crop. We conclude that while promise exists for high-yielding rice in aerobic soil, the rapid yield loss with successive rice cropping must first be overcome.
Grain crop response to contour hedgerow systems on sloping Oxisols
Farming systems that minimize the rate of soil degradation and optimize food crop yields are needed to sustain soil productivity on sloping, acid, infertile soils in the humid tropics. Research was conducted on two Oxisols with slopes ranging from 22 to 30% to evaluate the performance of several contour hedgerow systems, with and without the addition of 60 kg N ha1 per crop, on rice (Oryza sativa) and maize (Zea mays L.) production. Contour hedgerows were double rows of the tree legume Gliricidia sepium (G); Gliricidia and the native grass Paspalum conjugatum (GPas); Gliricidia and an exotic fodder grass Penisetum purpureum (GPen); double rows of Penisetum (Pen); and a conventional open field (C) farming system without hedgerows. Gliricidia prunings and all crop residues were applied to the soil surface in the alleys, but Penisetum was harvested. Food crop yields in all hedgerow treatments tended to be less than the Control for the first two years, presumably due to the displacement of land planted to the food crop. In the third and the fourth years, the rice and maize yields of Treatments G and GPas exceeded the Control, most consistently when N was not applied. Penisetum reduced food crop yields regardless of N application presumably due to nutrient removal in the fodder. The results indicate that Gliricidia in a contour hedgerow increases food crop yield on strongly acid Oxisols by recycling nutrients and partially supplementing the N demand by the food crops