M. Nagarajan
Introduction
Desertification is a land degradation process and it deals with the gradual conservation of productive land into less productive or unproductive ones. Thus, the problem is continuous one. The presence or absence of a nearby desert has no direct relation to desertification. Excess of land abuse in any patch or land necessary that suitable steps to be taken to control the desertification in arid region. In this regard, agroforestry is recognized as one of the efficient land use system to control desertification. Agroforestry by virtue of it merit has already earned distinct identification of its own and is so commonly used now a days. Agroforestry may simply be defined as an integrated self sustaining land management system, which involves delicate introduction and retention of woody components including trees, shrubs, bamboos, palm etc. with agricultural crops including pasture/livestock simultaneously or sequentially on the same unit of land meeting the ecological and socioeconomic needs of the people (Deb Roy, 1992; 1993). In arid regions, comprising sizeable area, the crop production levels are low, which to a large extent are due to low and erratic rainfall and low level of soil fertility. Accordingly most dwellers raise livestock as a subsidiary occupation and allow trees and shrubs to grown along with cultivated crops to mainly cover the risk and uncertainity of crop maturity. Malhotra et. Al. (1985) compiled the data on traditional agroforestry being practised by the farmers in the Rajasthan desert and delineated eight agroforestry zones and he also described trees, shrubs, grasses and crops in each of the zones.
Among the tree species P. Cineraria is an important leguminous tree and commonly known as khejri, widely distributed in western Rajasthan. In inhospitable dry climates, properly distributed this tree growth acts as a foster mother to agriculture. The agrarians well understood that the crop growth under P.cineraria based agroforestry system is better than the crops growing without trees in the same management conditions. The farmers of this region know the value of khejri tree. Ordinarily a cultivator hesitates to cut a khejri tree on his own field for fuel and thus one can find various tree density on the cultivate fields. Singh and Lal (1969), Aggarwal et al. (1976) and Shanker et al. (1976) have shown that the forage species produce higher biomass production under khejri tree canopy was due to high fertility status and thus P.cineraria holds an increasing important place in the economy of Indian desert. The farmers have been traditionally following agroforestry particularly intercropping of agricultural crops (til, bajra, moong, guar, etc.) With khejri and observed higher yields of crops, which could possibly due to the amelioration of harsh climate and the addition of nutrients through leaf fall. Some of the observations made in the traditional agroforestry field are being summarised in this article.
Effect of tree canopy on microbial and soil nutrients
The study of seasonal variation of microbial C, N and total C, N under the canopy also confirms that the tree plays a major role in nutrient buildup and the variations caused by this tree highly significant. In the month of March both microbial C, N and total C, N were recorded higher than the other months of year and the lease recorded in the month of July (Table 1). The role of Prosopis cineraria on microbial C, N and total C, N under the canopy is appreciable. Therefore, it is possible to develop an organic farm management practices in tillage with P.cineraria which can meet out the crop nutrient requirements to some extent. The quantity of available nutrients held in microbial biomass is considerable and it constitutes a transformation matrix for all natural organic materials in the soil and act as a source and sink of the nutrients.
Table 1. The microbial and soil C, N in the understorey soils of P.cineraria
|
Month |
Microbial carbon ug g |
Organic carbon mg 100g |
Microbial nitrogen ug g |
Total nitrogen mg 100g |
|
March |
1469.960 |
783.333 |
247.070 |
100.000 |
|
July |
491.014 |
571.612 |
51.404 |
87.500 |
Effect of tree canopy on Crop physiology
The study of eco-physiology of sesame crop grown under and over canopies revealed that photosynthetic pigments (Chlorophyll-a and b) were significantly higher in the under canopy crop plants than the over canopy. And though higher carotenoids too recorded in the under canopy plants, the difference is meagre (Table-2). The increased pigment contents of shade leaves has been attributed to the increase in number and size of chloroplast, the amount of chlorophyll pre-chloroplast and better grana development (Boardman, 1977). P.cineraria is well known for its ability to enhance available nutrients and water holding capacity of the under canopy soils (Gupta and Saxena, 1978). The higher water status in sesame is associated with higher chlorophyll content in a water stress study (Vyas et al., 1988).
Proline was higher in the leaves of sesame in the P.cineraria under canopy than over canopy. In sesame the plants in over canopy revealed higher soluble sugar than the under canopy, though the variation in insoluble sugar was meagre. Increase in water stress enhanced the reducing sugars contain in sesame (Vyas et al., 1988). Crude protein was higher in over canopy plants than under canopy plants (Table-2). Further studies may ascertain the cause (s), shade, water status or both, for the increased chlorophyll and protein in the under canopy of P.cineraria and soluble sugar and crude protein contents of the leaves of sesame in the over canopy.
Table 2. Proline, sugar and crude protein of sesame in agroforestry system (The values are the mean triplicate observations)
| Parameter | In under canopy | In over canopy |
|
Plant pigments (mg g-1 FW)
Chlorophyll-a
Chlorophyll-b
Carotenoid
Proline (u mole g-1 FW)
Sugar (mgg-1DW)
Soluble sugar
Insoluble sugar
Crude protein (mgg-1 DW) |
0.726
0.816
0.014
1.398259
28.44308
27.83354
177.0834 |
0.587
0.721
0.013
0.429965
51.17035
28.9868
213.5417 |
From the foregoing discussion it is evident that P.cineraria provides a better microhabitat below and around its canopy than the open field of the same piece of land. The leaves of P.cineraria rich in protein and mineral nutrients also bring the soil nutrients to upper layer. Therefore the purpose of synchronizing the release of nutrients from leaf litter with crop requirements (kharif and rabi cropping season) is to improve the ratio of nutrient uptake to losses by leaching. This in turn, will contribute to the efficiency of nutrient cycling in the nutrient ‘hunger’ soil. The designing synchronization of demand and supply of nutrients and tree canopy management for optimum benefit of crop yield are very essential area which need to be given attention by doing so, not only the crop productivity will get boost but also the desertification taken care in the extreme arid region.
Pertaining Literature
Aggarwal, R.K. Gupta, J.P. Saxena, S.K. and Muthana, K.D. 1976. Studies on soil physico-chemical and ecological changes under twelve years old five desert tree species of western Rajasthan. Indian Forester 102:863-872.
Boardman, N.K. 1977. Comparing photosynthesis of sun and shade plants. Ann. Rev. Plant Physiol. 28:355-377.
Deb Roy, 1992. Agroforestry in India Principles and Practices. In: Sustainable Development of Dryland Agriculture, (ed) R.P. Singh, Scientific Publisher, Jodhpur, pp. 393-413.
Deb Roy, 1993. Agroforestry system for enhanced fodder production. Souvenir on 32nd Foundation Day, IGFRI, Jhansi, Nov. 1, pp. 6-9.
Malhotra, S.P., Trivedi, H.S. and Mathur, Y.N. 1985, Agroforestry-a judicious use of desert ecosystem by man. CAZRI Pub. No. 27.
Mann, H.S.and Saxena, S.K. 1980. Role of Khejri in Agroforestry. In: Khejri (Prosopis cineraria) in the Indian Desert – Its Role in Agroforestry, eds. H.S. Mann and S.K. Saxena, Monograph No. 11, CAZRI, Jodhpur, pp. 64-67.
Shankar, V. 1984. Inter relationship of tree overstorey and understorey vegetation in silvipastoral system. In: Agroforestry in Arid and Semiarid Zones, ed. K.A. Shankarnarayan, CAZRI, Jodhpur, pp. 143-149.
Shankar V. Dadhich, N.K. and Saxena, S.K. 1976. Effect of khejri tree (Prosopis cineraria) on the productivity of range grasses growing in its vicinity. Forage Res. 2:91-96.
Singh, K.S. and Lal, P. 1969. Effect of khejri (Prosopis spicigera Linn.) And Babool (Acacia arabica) trees on the soil fertility and profile characteristic. Ann,Arid Zone 8:33-36.
Vyas, S.P., Garg, B.K. Kathju, S. And Lahiri, A.N. 1988. Improvement of drought tolerance in sesame (Sesamum indicum L.) Through early water stress.
M. Nagarajan
Central Arid Zone Research Institute
Regional Research Station
Jaisalmer 345 001
