Ryoichi Matsunaga

Field evaluation of nitrogen fixation and use of nitrogen fertilizer by sorghum/pigeonpea intercropping on an Alfisol in the Indian semi-arid tropics

A field experiment was conducted to obtain the N balance sheet for sole crops and intercrops of sorghum [Sorghum bicolor (L.) Moench] and pigeonpeas [Cajanus cajan (L.) Millsp.]. Intercropping gave a significant advantage over sole cropping in terms of dry matter production and grain yield, as calculated on the basis of the land equivalent ratio and area-time equivalent ratio. The N fertilizer use efficiency and atmospheric N2 fixation by pigeonpea were estimated using 15N-labeling and natural abundance methods. The N fertilizer use efficiency of sorghum was unaltered by the cropping system, while that of the pigeonpea was greatly reduced by intercropping. Although intercropping increased the fractional contribution of fixed N to the pigeonpeas, no significant difference was observed between the cropping systems in total symbiotically fixed N. There was no evidence of a significant transfer of N from the pigeonpea to the sorghum. This study showed that use of soil N and fertilizer N by pigeonpeas was almost the same as that by sorghum in sole cropping, indicating the potential competence of pigeonpeas to exploit soil N. However, when N was exhausted by a companion crop in intercropping, the pigeonpea crop increased its dependency on atmospheric N2 fixation. We conclude that knowledge of how N from different sources is shared by companion crops is a prerequisite to establishing strategies to increase N use, and consequently land productivity, in intercropping systems.

Nitrogen balance and root behavior in four pigeonpea-based intercropping systems

A medium-duration pigeonpea (Cajanus cajan L. Millsp.) is usually grown as intercrop. A wide range of crop combination in pigeonpea-based intercropping systems is found in India and eastern Africa (Ofroi and Stern, 1987; Rao and Willey, 1980; Venkateswarlu and Subramanian, 1990). Although much information is available on the production efficiency and monetary advantage of intercropping, very little is known about the nitrogen (N) economy and root behavior. The study was carried out to examine how the nitrogen balance sheet and root development of pigeonpea could be altered by companion crops.

Spatial distribution of root activity and nitrogen fixation in sorghum/pigeonpea intercropping on an Indian Alfisol

A medium-duration pigeonpea cultivar (ICP 1–6) and a hybrid sorghum (CSH 5) were grown on a shallow Alfisol in monocropping and intercropping systems. Using a monolith method, spatial distribution of nodulation, acetylene reduction activity (ARA) and root respiration were measured. The number, mass and ARA of nodules decreased exponentially with distance from the plant base except at the late reproductive stage. Nodulation and ARA tended to be higher in the intercrop than in the monocrop.

Kinetics of 15N-labelled nitrate uptake by maize (Zea mays L.) root segments

Abstract Isotherms and kinetic constants of nitrate uptake by excised root segments from the apical root zone of 6-d-old maize seedlings pretreated with nitrate were investigated using 15N-labelled nitrate. The isotherms were resolved into two systems namely a multiphasic saturable system at substrate concentrations lower than 2 mol m−-3 and a linear system at higher concentrations. The detailed analysis of the multiphasic saturable system suggested the existence of at least three phases, which followed the Michaelis-Menten kinetics. The I max and K m of each phase increase from the lower phase to the upper phase. The distance from the root tip and the presence of stele affected considerably the linear system but only slightly the saturable system.

Response of short-duration pigeonpea to nitrogen application after short-term waterlogging on a Vertisol

Abstract Short-duration pigeonpea suffers from waterlogging damage following heavy rainfall at the pre-flowering stage on soils with high clay content, such as Vertisols. Effects of short-term waterlogging (3 d) on shoot and root growth of short-duration pigeonpea grown on a Vertisol field were quantified, and the alleviation of waterlogging damage by top-dressing of nitrogen fertilizer was examined. Reduced leaf chlorophyll, increased senescence and abscission of lower leaves were observed within 3 d of the initiation of waterlogging. Root growth and symbiotic N2 fixation were also severely impaired. Root distributions of waterlogged plants were shallower than those of the control during the subsequent recovery period because new adventitious roots were formed in the shallow rather than deep soil layer. Yield of waterlogged crops was significantly smaller than the control. Top-dressing of nitrogen at one day after the termination of waterlogging alleviated waterlogging damage either completely or partially. Leaf chlorophyll and shoot dry mass of waterlogged plants were 78 and 84% of the values in control plants immediately after waterlogging but recovered to 92 and 98% of the control values at the pod-filling stage with a top-dressing of 50 kg N ha−1. Nitrogen application promoted root growth in the shallow soil layers during the first 11 d after application, and in the deeper soil layers during the subsequent 16 d. Total nodule activity was significantly reduced by 100 kg N ha−1, but increased by 50 kg N ha−1 around one month after the top-dressing. The reduction in seed yield was largely compensated for by 50 kg N ha−1, because of recovery from waterlogging damage to shoot and root growth involving increased nodule activity.

Simulating root system development of short-duration pigeonpea

Length and weight of pigeonpea roots were measured weekly in different soil layers and compared with estimates obtained from a root simulation model using daily climatic data, soil physico-chemical properties and dry matter allocation to roots. Daily moisture content and temperature at different soil depths were well simulated using sub-routines from the CERES-Maize model. Daily allocation of dry matter to roots was calculated from logistic functions fitted to the growth data for shoots and roots. Although root length and weight tended to be underestimated by the model, regressions between measured and simulated root growth were highly significant so that the model could, with a few modifications, be used to predict root system development.

Applicability of phosphate buffer extractable organic nitrogen as an indicator of available nitrogen in the sandy soils of the Sahel zone of Niger, West Africa

Abstract As phosphate buffer extractable organic nitrogen (PEON) has been successfully used to evaluate the available nitrogen in Japanese soils, we tested whether it could also be used with sandy soils of the Sahel zone of Niger. Soils were collected from 33 farm fields in the Fakara region of Niger. Pearl millet (Pennisetum glaucum L. cv. Haini–Kirei) was grown in these soils for 4 weeks with all nutrients except nitrogen supplied, and plant nitrogen uptake was measured. We analyzed PEON, the inorganic and total nitrogen present at the start of the experiment, and the nitrogen mineralized during incubation in the same soils. Both PEON and mineralizable nitrogen were significantly correlated with nitrogen uptake by pearl millet. The PEON + inorganic nitrogen and mineralizable nitrogen + inorganic nitrogen were also significantly correlated with nitrogen uptake. Unlike in Japanese soils, the correlation between PEON and mineralizable nitrogen was not high in the sandy Sahelian soils. The absorbance at 280 nm and the content of Coomassie Blue reactive substances detected using the Bradford method for soil extracts treated with 0.067 mol L−1 phosphate buffer were highly correlated with nitrogen uptake by pearl millet. These results suggest that extraction with 0.067 mol L−1 phosphate buffer is a convenient method for evaluating the available nitrogen in sandy Sahelian soils.

Identification of Plant Genetic Resources with High Potential Contribution to Soil Fertility Enhancement in the Sahel, with Special Interest in Fallow Vegetation

The sandy soil in the Sahel is characterized as low inherent fertility, that is, having nutrient deficiency (total N and available P), low organic matter and high risk of erosion. Under the concept of integrated soil fertility management (ISFM), possible contribution of natural inhabitant plants to the improvement of soil fertility in the Sahel was evaluated. A broad variation in δ 15N values was observed among the plant species commonly found in cropland and fallow land of the Sahelian zone. Annual leguminous herbs, Cassia mimosoides (Caesalpiniaceae) and Alysicarpus ovalifolius (Papilionaceae), had low δ 15N values, showing their higher dependency on biological nitrogen fixation. They will be efficiently utilized as an extensive means of soil fertility management, for example, through more encouraged incorporation into the fallow vegetation. Ctenium elegans, Eragrostis tremula and Schizachyrium exile, greatly dominating annual grass species in the fallow land, though their δ 15N values were high, would contribute to the soil fertility by supplying a significant amount of organic matter.

Nitrogen fertilizer management in pigeonpea/sorghum intercropping on an Alfisol in the semi-arid tropics

Three methods of N fertilizer application, basal broadcasting, basal banding and split banding, were compared in terms of yield production, fertilizer use efficiency in sole crop and intercrops of sorghum and pigeonpea. The yield production was maintained unchanged by application methods. Nitrogen fertilizer use efficiency was improved by basal banding and split banding. It is concluded that application of N fertilizer to sorghum rows by banding will improve the efficiency of fertilizer utilization by crops which are grown alone or with component crops without affecting yield production.