Thesis Abstract of AGS Students

Productivity of maize/lablab intercrop

Naba Raj Devkota (1993)

Agriculture is the mainstay of Nepalese economy. Crops and animal production are two major agricultural enterprises with predominantly small farm based. Crop yields are low and unstable, by-products are not enough to feed the animals. Findings from informal survey and discussion with key informants suggested the possibility of maize (Zea mays L.)/lablab (Lablab purpureus L. Sweet) intercropping that could be helpful to solve the fodder scarcity problem in Chitawon, Nepal.

This study was designed to determine productivity of maize/lablab intercrop system, in terms of grain yield of maize, biomass and fodder yield of labla as well as input from nitrogen fixation. The experiment was located at the university of Chiang Mai field station (18.48 ^oN, 98.59 ^oE), on a sandy loam (San Sai series) of pH 6.35. Out of the total eleven treatments used, eight were factorial combinations of two lablab cropping systems (i.e., mono and intercropped with maize), two dates of lablab cutting (40 DAS and 60 DAS) and two cutting heights (30 and 20 cm from the base). Remaining three treatments were mono and intercropped lablab without cutting and monoculture maize. The treatments were arranged in RCBD with four replicates. The additive series design was used to compare monocultures (53,333 plants ha-1) and intercrops (80,000 plants ha-1). Grain yield of maize was determined at final harvesting. Dry matter of maize at four times and lablab at five times were estimated during the entire crop growth duration. At each time of dry matter determination of lablab, amounts of nitrogen fixation were also quantified from the ureide analysis of collected root bleeding sap.

In monoculture, the maize grain yield was 3.17 Mg ha-1. Intercropping with lablab had no significant effect (P < 0.05) on the maize yield. Cutting the intercropped lablab at 40 DAS, either to 20 or 30 cm height from the base, actually increased the maize yield (P < 0.05) to 3.82 Mg ha-1. However, if cutting was delayed to 60 DAS, there was no increase (P < 0.05) in grain yield. This suggests the positive effect on yield of maize when cutting lablab at appropriate time (40 DAS).

Monocropped and intercropped lablab without cutting fixed 339.80 and 257.40 kg ha-1 of total nitrogen respectively at final harvesting (130 DAS). Cutting reduced amount of fixation in intercrop more than in monocrop. However, reduction was less if lablab was cut at 40 DAS (37%) than when cut at 60 DAS (71%). There were no significant differences observed between two cutting height both in mono and intercrop. Intercropped lablab cutting at 40 DAS derived a higher percentage of total N from fixation (88%) than the monoculture of same cut (81%) at 130 DAS. Such higher dependency on fixation could be associated with the reduced uptake of soil N which could have stimulated lablab to be more relied upon nitrogen fixation.

Intercropped maize and lablab yields, whether in terms of LER's of dry matter at maize harvesting (1.28 to 1.65) or ATER's for dry matter (1.09 to 1.44) at final harvesting all indicated a definite advantage of intercropping compared with their monoculture yields. In addition to above relative advantage, intercropped maize had also absolute advantage over monoculture by about 30% in terms of dry matter production. Cutting lablab in the intercrop, however, depressed this advantage slightly.

This study reveals that lablab can be introduced as a component crop in an intercropping with maize that increased the productivity of land. Managing lablab with cutting proved to be an effective way to maximize the systems benefits, but cutting has to be done at the right time. Although fixation from the atmosphere contributed 88% of the lablab nitrogen, there is a danger that soil nitrogen may be depleted under such system if all of the lablab biomass is removed from the field. The attention to the management of lablab biomass, recycling of nutrients in the form of farm yard manure will be essential to the maintenance of the high level of productivity in the long run.

Back to Thesis Topics